Machine tool

Abstract

To provide a machine tool which can estimate gripping force of a workpiece with high accuracy.SOLUTION: A machine tool includes: a first main shaft 4 which has a collet chuck 48 and rotates; an air cylinder 32 which reduces the diameter of the collet chuck 48 by moving a piston 322 to one side by supplying air to a first pressure chamber 324 and enlarges the diameter of the collet chuck 48 by moving the piston 322 to the other side by supplying air to a second chamber 325; a first pressure sensor 3261 which measures a first pressure to be pressure of air supplied to the first pressure chamber 324 when moving the piston 322 to the one side; a second pressure sensor 3271 which measures a second pressure to be pressure of air flowing out from the second pressure chamber 325 when moving the piston 322 to the one side; and an estimation section 23 which estimates the gripping force of the collet chuck 48 on the basis of the differential pressure between the first pressure measured by the first pressure sensor 3261 and the second pressure measured by the second pressure sensor 3271.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

[0002] Machine tools for machining a bar-shaped workpiece held by a spindle rotatable about a spindle center line are known. This spindle is rotatably supported by a spindle headstock. The spindle is provided with a gripping portion that grips the workpiece by reducing its diameter and releases the gripping of the workpiece by increasing its diameter. The gripping portion is operated by an actuator fixed to the spindle headstock (see, for example, Patent Document 1). In the machine tool of this Patent Document 1, the shifter is displaced by driving the actuator, so that the claw member swings, and the chuck sleeve moves along the spindle center line via a push sleeve, thereby gripping or releasing the workpiece by the gripping portion. As this actuator, a fluid pressure cylinder such as an air cylinder or a hydraulic cylinder may be used.

[0003] In addition, a general spindle is provided with an adjusting nut as an adjusting means for adjusting the gripping force of the workpiece. This adjusting nut is attached to the spindle body so as to be relatively rotatable with respect to the spindle body, and by rotating it, the position of the adjusting nut in the spindle center line direction with respect to the spindle body is displaced, and the gripping force of the workpiece changes. When machining a workpiece having a different diameter or a different material from the workpiece that has been machined so far, the operator of the machine tool inserts the next workpiece to be machined into the gripping portion in a so-called setup operation and relatively rotates the adjusting nut with respect to the spindle body to adjust the gripping force of the workpiece. Then, the operator of the machine tool manually operates a shifter lever for displacing the shifter, estimates the gripping force of the gripping portion from the force required for the operation, and repeatedly rotates and estimates the adjusting nut until the desired gripping force is reached, and then fixes the adjusting nut to the spindle body at a position where the desired gripping force is considered to have been obtained.

Prior Art Documents

Patent Documents

[0004] Patent Document 1 Japanese Patent Application Laid-Open No. 2020-97075 Summary of the Invention Problems to be Solved by the Invention

[0005] However, in the conventional adjustment method, since the gripping force is estimated depending on the operator's feeling, there is a problem that the estimation accuracy of the gripping force is low. Further, after adjustment in the setup work, the gripping force may change due to wear or thermal displacement of the mechanism intervening between the fluid pressure cylinder such as the shifter and the claw member and the gripping portion, deterioration of the rubber packing of the fluid cylinder, or variation in the work diameter. For this reason, the gripping force of the work during processing may be different from the gripping force estimated at the time of adjustment.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a machine tool capable of estimating the gripping force of a work with high accuracy. Means for Solving the Problems

[0007] The machine tool of the present invention for solving the above problems is provided with a gripping portion that grips a work by reducing its diameter and releases the gripping of the work by expanding its diameter, a spindle that rotates about the spindle center line as a rotation center, and a fluid pressure cylinder having a first pressure chamber and a second pressure chamber partitioned by a piston, moving the piston to one side by supplying fluid to the first pressure chamber to reduce the diameter of the gripping portion, and moving the piston to the other side by supplying fluid to the second pressure chamber to expand the diameter of the gripping portion, and a first pressure sensor that measures a first pressure which is the pressure of the fluid supplied to the first pressure chamber when the piston is moved to the one side, and a second pressure sensor that measures a second pressure which is the pressure of the fluid flowing out from the second pressure chamber when the piston is moved to the one side, and It is characterized by including an estimation unit that estimates the gripping force of the gripping part based on the differential pressure between the first pressure measured by the first pressure sensor and the second pressure measured by the second pressure sensor.

[0008] According to this machine tool, since the gripping force is estimated based on the differential pressure which is the driving force for actually operating the fluid pressure cylinder, the gripping force of the workpiece can be estimated with high accuracy.

[0009] Here, the main shaft has a claw member that opens and closes the gripping part by swinging, and a shifter that swings the claw member by displacing along the main shaft center line. The fluid pressure cylinder may be one that displaces the shifter along the main shaft center line by moving the piston to one side and the other side by the pressure of the fluid. Also, the main shaft may have an adjustment means for adjusting the gripping force of the workpiece by the gripping part. The estimation unit may estimate the gripping force of the gripping part based on the differential pressure when the piston moves to the one side. This machine tool may be provided with conversion information storage means in which the conversion information between the differential pressure and the gripping force is stored.

[0010] In this machine tool, The estimation unit may estimate the gripping force based on the differential pressure a predetermined time before the piston reaches the arrival point on the one side.

[0011] By doing so, it is only necessary to store the differential pressure information for the predetermined time in the storage means, so the storage area of the storage means required to store the information can be reduced.

[0012] Here, the fluid pressure cylinder may have an end sensor that detects that the piston has reached the arrival point on the one side. The arrival point may be a stroke end where the piston rod has moved to the most one side. This machine tool may include a differential pressure information storage unit that sequentially stores the differential pressure. Further, the estimation unit may acquire information on the differential pressure before the predetermined time from the differential pressure information storage unit. The estimation unit may estimate the gripping force based on the differential pressure after the piston located on the other side starts to move to the one side. In other words, the estimation unit may estimate the gripping force based on the differential pressure after fluid starts to be supplied to the first pressure chamber.

[0013] In this machine tool, the estimation unit may estimate the gripping force based on the maximum value of the differential pressure in a predetermined time range before the piston reaches the arrival point on the one side.

[0014] By doing so, the gripping force can be estimated more accurately.

[0015] Here, the estimation unit may acquire information on the differential pressure in the predetermined time range from the differential pressure information storage unit.

[0016] In this machine tool, the estimation unit may determine whether the differential pressure is within a predetermined range, and if it exceeds the predetermined range, determine that there is an abnormality in the gripping force.

[0017] In this mode, the operator of this machine tool can easily recognize the abnormality in the gripping force.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a machine tool capable of estimating the gripping force of a workpiece with high accuracy.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, an example in which the present invention is applied to a Swiss-type NC (Numerical Control) lathe will be described.

[0021] FIG. 1 is a plan view simply showing the internal configuration of the NC lathe 1 according to this embodiment.

[0022] As shown in FIG. 1, inside the NC lathe 1, there are provided a control device 2, a first spindle headstock 3, a first spindle 4, a guide bushing 5, a first tool post 6, a second spindle headstock 7, a second spindle 8, and a second tool post 9. The control device 2 is a computer that operates the first spindle headstock 3, the first spindle 4, the first tool post 6, the second spindle headstock 7, the second spindle 8, and the second tool post 9 according to an NC program. In addition to the operation using the NC program, the NC lathe 1 can also be operated by directly inputting a command from the operation unit 11 (see FIG. 7) to the control device 2.

[0023] The first spindle headstock 3 moves in the Z1-axis direction together with the first spindle 4 by a signal from the control device 2. The Z1-axis direction is a horizontal direction and is the left-right direction in FIG. 1. The first spindle 4 is rotatably mounted on the first spindle headstock 3. Further, a first spindle motor 31 (see FIG. 2) is provided between the first spindle headstock 3 and the first spindle 4. When the first spindle motor 31 receives a signal from the control device 2 and rotates, the first spindle 4 rotates about the first spindle center line CL1. The direction of this first spindle center line CL1 coincides with the Z1-axis direction.

[0024] The first spindle 4 changes its state between a gripping state in which a long bar-shaped workpiece W1 inserted therein is gripped and a gripping release state in which the gripping of the workpiece W1 is released by a signal from the control device 2. This first spindle 4 corresponds to an example of a spindle. When the first spindle motor 31 (see FIG. 2) receives a signal from the control device 2 and rotates, the workpiece W1 gripped by the first spindle 4 rotates about the first spindle center line CL1 together with the first spindle 4. The configurations of the first spindle headstock 3 and the first spindle 4 will be described in detail later.

[0025] The guide bush 5 is fixed to the legs that are the base of the NC lathe 1. The guide bush 5 is inserted into the inside of the first spindle 4 and slidably supports the tip portion of the workpiece W1 whose tip protrudes from the first spindle 4 in the Z1-axis direction. The portion of this guide bush 5 that supports the workpiece W1 is rotatable about the first spindle center line CL1 in synchronization with the first spindle 4. That is, the first spindle center line CL1 is also the rotation center line of the portion of the workpiece W1 supported by the guide bush 5. The presence of the guide bush 5 suppresses the deflection of the workpiece W1 during machining, so that particularly long and slender workpieces W1 can be machined with high precision.

[0026] The first tool post 6 is movable in the X1-axis direction that is orthogonal to the Z1-axis direction and faces the horizontal direction, and in the Y1-axis direction that faces the vertical direction. The first tool post 6 moves in the X1-axis direction and the Y1-axis direction in response to a signal from the control device 2. In FIG. 1, the vertical direction is the X1-axis direction, and the direction orthogonal to the paper surface is the Y1-axis direction. A first spindle tool T1 for machining the workpiece W1 is mounted on the first tool post 6. FIG. 1 shows a state in which the first spindle tool T1 is mounted on the first tool post 6. A plurality of types of first spindle tools T1 including a tool for outer diameter machining, a tool for parting, etc. are arranged side by side in the Y1-axis direction on the first tool post 6. By moving the first tool post 6 in the Y1-axis direction, any one of these plurality of types of first spindle tools T1 is selected. Then, by moving the first tool post 6 in the X1-axis direction, the selected first spindle tool T1 cuts into the workpiece W1 held by the first spindle 4 to machine the workpiece W1.

[0027] The second spindle headstock 7 moves in the X2-axis direction and the Z2-axis direction together with the second spindle 8 in response to a signal from the control device 2. The X2-axis direction is the same direction as the above-described X1-axis direction, and the Z2-axis direction is the same direction as the above-described Z1-axis direction. A second spindle motor (not shown) such as a built-in motor is provided on the second spindle headstock 7. When the second spindle motor rotates in response to a signal from the control device 2, the second spindle 8 rotates about the second spindle center line CL2. The direction of the second spindle center line CL2 coincides with the Z2-axis direction.

[0028] On the second main spindle 8, after the machining using the first main spindle 4 is completed, the cut workpiece W2 cut by the tool for parting is delivered. The second main spindle 8 changes its state between a gripping state in which the cut workpiece W2 delivered from the first main spindle 4 is gripped and a gripping release state in which the gripping of the cut workpiece W2 is released. This second main spindle 8 also corresponds to an example of a main spindle. When the second spindle motor rotates in response to a signal from the control device 2, the workpiece W2 gripped by the second main spindle 8 rotates about the second main spindle center line CL2 together with the second main spindle 8.

[0029] The second tool rest 9 moves in the Y2-axis direction according to a signal from the control device 2. This Y2-axis direction is the same direction as the above-described Y1-axis direction, that is, the vertical direction. A plurality of tools T2 for the second main spindle for machining the cut workpiece W2 gripped by the second main spindle 8 are mounted on the second tool rest 9. FIG. 1 shows a state in which the tool T2 for the second main spindle is mounted on the second tool rest 9. A plurality of types of tools T2 for the second main spindle, such as drills and end mills, are attached to the second tool rest 9. Although not shown in FIG. 1, the tools T2 for the second main spindle are arranged side by side not only in the X2-axis direction but also in the Y2-axis direction. By the movement of the second main spindle base 7 in the X2-axis direction and the movement of the second tool rest 9 in the Y2-axis direction, an arbitrary tool T2 for the second main spindle is selected from these plurality of types of tools T2 for the second main spindle. Then, when the second main spindle base 7 moves in the Z2-axis direction, the cut end side portion of the cut workpiece W2 gripped by the second main spindle 8 is machined.

[0030] FIG. 2 is a cross-sectional view taken from above after cutting the first main spindle base 3 and the first main spindle 4 shown in FIG. 1 with a horizontal plane passing through the first main spindle center line CL1. Further, FIG. 3 is an enlarged view of the first main spindle 4 shown in FIG. 2. These FIGS. 2 and 3 show the first main spindle base 3 and the first main spindle 4 in the gripping release state. Note that in FIGS. 2 and 3, hatching indicating the cross section is not shown.

[0031] As shown in Fig. 2, the first main shaft 4 generally has a cylindrical shape with an axis in the direction of the first main shaft center line CL1. The first main shaft 4 is rotatably supported by a bearing 39 on the first main shaft base 3. The first main shaft 4 includes a main shaft body 41, a shifter 42, a claw 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. This collet chuck 48 corresponds to an example of a gripping portion.

[0032] The main shaft body 41 is a cylindrical body extending in the Z1-axis direction and serving as the base of the first main shaft 4. The shifter 42 is disposed on the rear end side of the first main shaft 4. The shifter 42 generally has a cylindrical shape and is attached to the main shaft body 41 so as to be slidable in the Z1-axis direction by the inner peripheral surface being in sliding contact with the outer peripheral surface of the main shaft body 41. In Figs. 2 and 3, the left side of the figure is the rear end side of the first main shaft 4. As shown in Fig. 3, a cam surface 42a and a groove 42b are formed on the outer peripheral surface of the shifter 42. The cam surface 42a is composed of a small-diameter surface 42a1 having the smallest and constant outer diameter, a changing surface 42a2 with a gradually increasing outer diameter, and a large-diameter surface 42a3 having the largest and constant outer diameter, in order from the rear end side of the first main shaft 4. This shifter 42 slides in the Z1-axis direction by an air cylinder 32 (see Fig. 2) whose operation is controlled by a control device 2 (see Fig. 1). Figs. 2 and 3 show the state where the shifter 42 is located at the initial position closest to the tip end side of the first main shaft 4. In Figs. 2 and 3, the right side of the figure is the tip end side of the first main shaft 4.

[0033] Two claw members 43 are attached to the main shaft body 41 so as to be swingable about a claw shaft 431. A claw tip portion 43b acting as a cam follower in contact with the cam surface 42a of the shifter 42 is formed at the tip end portion of this claw member 43. As the shifter 42 slides, the claw tip portion 43b approaches or separates from the first main shaft center line CL1 along the cam surface 42a, causing the claw member 43 to swing about the claw shaft 431 as the swing center. A sleeve pressing portion 43a is formed on the claw member 43, and the sleeve pressing portion 43a is in contact with the rear end of the push sleeve 45.

[0034] The adjusting nut 44 is screwed to the spindle body 41 at the rearmost end portion of the first spindle 4. This adjusting nut 44 corresponds to an example of an adjusting means. A female screw is formed inside the adjusting nut 44, which meshes with a male screw formed at the rear end portion of the spindle body 41. By rotating the adjusting nut 44 in the tightening direction, the claw member 43, the push sleeve 45, and the chuck sleeve 46 move toward the tip side of the first spindle 4 together with the adjusting nut 44. As a result, the inner diameter of the collet chuck 48 in the gripping state becomes relatively smaller, and the gripping force of the workpiece W1 of the first spindle 4 increases. On the other hand, by rotating the adjusting nut 44 in the loosening direction, the claw member 43, the push sleeve 45, and the chuck sleeve 46 move toward the rear end side of the first spindle 4 together with the adjusting nut 44. As a result, the inner diameter of the collet chuck 48 in the gripping state becomes relatively larger, and the gripping force of the workpiece W1 of the first spindle 4 decreases. That is, the gripping force of the workpiece W1 of the first spindle 4 is adjusted by the adjusting nut 44. The adjusting nut 44 has a C shape with a notch along the radial direction when viewed from the rear end side to the tip side of the first spindle 4, and the width of the notch portion can be changed by a screw (not shown). After the adjustment of the gripping force using the adjusting nut 44 is completed, the adjusting nut 44 is fixed to the spindle body 41 at the adjusted position by narrowing the notch portion with the screw. Note that the gripping force of the workpiece W1 of the first spindle 4 may be adjusted using an adjusting means other than the adjusting nut 44.

[0035] The push sleeve 45 is a cylindrical body disposed inside the spindle main body 41, and its tip contacts the rear end portion of the chuck sleeve 46. The push sleeve 45 and the chuck sleeve 46 move in a direction opposite to the shifter 42 by the movement of the shifter 42 in the Z1-axis direction. Specifically, when the shifter 42 slides to the rear end side of the first spindle 4, the claw tip portion 43b of the claw member 43 is pushed up by the cam surface 42a of the shifter 42 and moves in a direction away from the first spindle center line CL1. As a result, the upper claw member 43 in FIG. 3 swings counterclockwise with the claw shaft 431 as the swing center, and the lower claw member 43 in FIG. 3 swings clockwise, and the push sleeve 45 and the chuck sleeve 46 are pushed by the sleeve push portion 43a of the claw member 43 and move to the tip side of the first spindle 4. In the process of the claw tip portion 43b being pushed up by the cam surface 42a of the shifter 42, when the contact point between the claw tip portion 43b and the cam surface 42a reaches the boundary point between the changing surface 42a2 and the large-diameter surface 42a3, the collet chuck 48 is in the most closed state and the first spindle 4 is in the gripping state. And when the workpiece W1 (see FIG. 1) is inside the collet chuck 48, the force of the air cylinder 32 (see FIG. 2) at that moment is substantially proportional to the gripping force for gripping the workpiece W1. The force of the air cylinder 32 at this time is based on the differential pressure between the pressure of the air supplied to the first pressure chamber 324 (see FIG. 2) and the pressure of the air discharged from the second pressure chamber 325 (see FIG. 2), so the above-mentioned differential pressure at that moment is substantially proportional to the gripping force of the workpiece W1. Hereinafter, the differential pressure at the moment when the contact point between the claw tip portion 43b and the cam surface 42a reaches the boundary point between the changing surface 42a2 and the large-diameter surface 42a3 may be referred to as the effective differential pressure.

[0036] Conversely, when the shifter 42 slides to the tip side of the first spindle 4, the claw tip portion 43b of the claw member 43 moves along the cam surface 42a of the shifter 42 in a direction approaching the first spindle center line CL1. As a result, the upper claw member 43 in FIG. 3 swings clockwise with the claw shaft 431 as the swing center, and the lower claw member 43 in FIG. 3 swings counterclockwise, and the push sleeve 45 and the chuck sleeve 46 move to the rear end side of the first spindle 4.

[0037] The coil spring 47 constantly pushes the chuck sleeve 46 toward the rear end side and constantly pushes the collet chuck 48 toward the front end side. As a result, the push sleeve 45 is also pushed toward the rear end side via the chuck sleeve 46, and the rear end of the push sleeve 45 pushes the sleeve push portion 43a toward the rear end side.

[0038] The inner peripheral surface 46a of the tip portion of the chuck sleeve 46 is a tapered surface whose diameter increases toward the front end side. The collet chuck 48 is configured to be able to expand and contract in the radial direction orthogonal to the first spindle center line CL1. The outer peripheral surface 48a of the tip portion of the collet chuck 48 is a tapered surface whose diameter increases toward the front end side. Three slits are formed in the collet chuck 48 at intervals of 120° in the circumferential direction, continuously from the tip to near the center in the Z1 axis direction. Due to these holes and slits, the tip side of the collet chuck 48 can expand and contract in the radial direction. In the gripping release state shown in FIGS. 2 and 3, since the chuck sleeve 46 is located on the rear end side, there is almost no force for the inner peripheral surface 46a of the tip portion of the chuck sleeve 46 to push the outer peripheral surface 48a radially inward, and the tip side of the collet chuck 48 expands in the radial direction due to its own elasticity.

[0039] The spindle cap 49 is in the shape of a bowl with a circular cap through hole penetrating in the Z1 axis direction formed in the central portion. The spindle cap 49 regulates the movement of the collet chuck 48 toward the front end side by the tip surface of the collet chuck 48 contacting the portion corresponding to the bottom of the bowl shape. The collet chuck 48 is constantly pressed against the spindle cap 49 by being pushed by the coil spring 47. The spindle cap 49 is fixed to the spindle body 41 by a female screw portion formed inside the edge of the bowl shape engaging with a male screw portion formed at the tip portion of the spindle body 41.

[0040] As shown in Fig. 2, the first spindle head 3 has 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 on the first spindle head 3. As described above, by rotationally driving the first spindle motor 31, the first spindle 4 supported by the first spindle head 3 via the bearing 39 rotates about the first spindle center line CL1.

[0041] The air cylinder 32 has a cylinder tube 321, a piston 322, and a piston rod 323. This air cylinder 32 corresponds to an example of a fluid pressure cylinder. Also, the air supplied to this air cylinder 32 corresponds to an example of a fluid. Note that a hydraulic cylinder such as a hydraulic cylinder may be used instead of the air cylinder 32. The cylinder tube 321 is the housing of the air cylinder 32 and has a cylindrical shape. The piston 322 is disposed in the cylinder tube 321 so as to be movable on one side and the other side in contact with the inner peripheral surface of the cylinder tube 321. By this piston 322, the inside of the cylinder tube 321 is partitioned into a first pressure chamber 324 and a second pressure chamber 325.

[0042] The piston rod 323 has a rod shape with one end fixed to the piston 322. The other end of the piston rod 323 is connected to the shifter lever 33.

[0043] The air cylinder 32 is provided with a first port 326 that is connected to the first pressure chamber 324 and supplies air to the first pressure chamber 324, and a second port 327 that is connected to the second pressure chamber 325 and supplies air to the second pressure chamber 325. By supplying air to the first pressure chamber 324 and exhausting the air in the second pressure chamber 325, the piston 322 moves to one side, and the extension length of the piston rod 323 that has advanced to the other side from the cylinder tube 321 becomes shorter. Also, by supplying air to the second pressure chamber 325 and exhausting the air in the first pressure chamber 324, the piston 322 moves to the other side, and the extension length of the piston rod 323 that has advanced to the other side from the cylinder tube 321 becomes longer. FIG. 2 shows a state where the piston 322 has moved to the other side most and the extension length of the piston rod 323 has become longer.

[0044] The shifter lever 33 is swingable about the lever shaft 331 as a swing center. One end of the shifter lever 33 is rotatably connected to the other end of the piston rod 323 by a connecting pin 332. Also, the other end of the shifter lever 33 fits into the groove 42b of the shifter 42. By driving the air cylinder 32, the shifter lever 33 swings, and due to this swing, the shifter 42 slides in the Z1-axis direction. The air cylinder 32, shifter lever 33, shifter 42, claw member 43, push sleeve 45, chuck sleeve 46, coil spring 47, and collet chuck 48 described above form a collet opening and closing mechanism for expanding and contracting the collet chuck 48.

[0045] FIG. 4 is a perspective view of the first spindle head 3 and the first spindle 4 shown in FIG. 1. This FIG. 4 also shows the first spindle head 3 and the first spindle 4 in the gripping release state.

[0046] As shown in FIG. 4, a first pressure sensor 3261 for measuring the pressure of air supplied to or discharged from the first pressure chamber 324 (see FIG. 2) is provided at the first port 326 of the air cylinder 32. Hereinafter, the pressure of the air measured by the first pressure sensor 3261 may be referred to as the first pressure. Further, a second pressure sensor 3271 for measuring the pressure of air supplied to or discharged from the second pressure chamber 325 (see FIG. 2) is provided at the second port 327 of the air cylinder 32. Hereinafter, the pressure of the air measured by the second pressure sensor 3271 may be referred to as the second pressure. By supplying air to the first pressure chamber 324 through the first port 326, the piston 322 (see FIG. 2) moves to one side and the collet chuck 48 (see FIG. 2) contracts in diameter, and the first main shaft 4 changes its state from the gripping release state shown in FIGS. 2 to 4 to the gripping state.

[0047] FIG. 5 is a cross-sectional view similar to FIG. 2 showing the first main shaft base 3 and the first main shaft 4 in the gripping state. In FIG. 5, hatching indicating the cross-section is not shown.

[0048] As described above, when air is supplied to the first pressure chamber 324, the air that was previously in the second pressure chamber 325 is pushed out and exhausted through the second port 327, and the piston 322 moves to one side. As a result, as shown in FIG. 5, the advancing length of the piston rod 323 becomes shorter, the shifter 42 slides to the rear end side of the first main shaft 4, the tip end portion 43b moves away from the first main shaft center line CL1, and the push sleeve 45 and the chuck sleeve 46 move to the tip end side of the first main shaft 4. Then, due to the tapered surface of the inner peripheral surface 46a at the tip end of the chuck sleeve 46 and the tapered surface of the outer peripheral surface 48a at the tip end of the collet chuck 48, the tip end side of the collet chuck 48 contracts in the radial direction against the elasticity of the collet chuck 48 itself, and the first main shaft 4 enters the gripping state of gripping the workpiece W1 (see FIG. 1).

[0049] Conversely, when air is supplied to the second pressure chamber 325, the air that was previously in the first pressure chamber 324 is pushed out and exhausted through the first port 326, and the piston 322 moves to the other side. As a result, as shown in FIG. 2, the extension length of the piston rod 323 becomes longer and the shifter 42 slides to the tip side of the first main shaft 4. Then, by the restoring force of the coil spring 47, the push sleeve 45 and the chuck sleeve 46 move to the rear end side of the first main shaft 4, the claw member 43 swings, and the claw tip portion 43b approaches the first main shaft center line CL1. And since the force that the inner peripheral surface 46a of the tip portion of the chuck sleeve 46 presses the outer peripheral surface 48a of the tip portion of the collet chuck 48 radially inward decreases or disappears, the tip side of the collet chuck 48 expands radially by the elasticity of the collet chuck 48 itself, and the first main shaft 4 enters a gripping release state in which gripping of the workpiece W1 (see FIG. 1) is released.

[0050] FIG. 6 is a pneumatic circuit diagram for changing the state of the first main shaft 4 shown in FIG. 1 between a gripping state and a gripping release state.

[0051] As shown in FIG. 6, the air cylinder 32 has an end sensor 328. The end sensor 328 detects that the piston 322 has moved to the most one side and transmits an arrival signal to the control device 2 (see FIG. 1). The air that drives the air cylinder 32 is supplied from a pressure source 34 installed in a factory or the like where the NC lathe 1 (see FIG. 1) is arranged. This pressure source 34 is, for example, an air compressor. The air supplied from the pressure source 34 has its supply destination switched by a switching valve 35 that is switched and controlled by the control device 2, and is supplied to one of the first pressure chamber 324 and the second pressure chamber 325. FIG. 6 shows a state in which air is being supplied to the second pressure chamber 325.

[0052] The switching valve 35 switches the supply destination of the air from the pressure source 34 according to the switching signal from the control device 2, and switches the discharge destination of the air discharged from the air cylinder 32 to one of the first exhaust port 36A and the second exhaust port 36B. In the present embodiment, when air is supplied from the pressure source 34 to the first pressure chamber 324 and the piston 322 moves to one side, the air in the second pressure chamber 325 is exhausted from the second exhaust port 36B. Conversely, when air is supplied from the pressure source 34 to the second pressure chamber 325 and the piston 322 moves to the other side, the air in the first pressure chamber 324 is exhausted from the first exhaust port 36A. Note that silencers for reducing the exhaust noise are provided at the first exhaust port 36A and the second exhaust port 36B, respectively.

[0053] As described above, the first pressure sensor 3261 measures the air pressure which is the pressure of the fluid in the first port 326 immediately before the first pressure chamber 324. Further, the second pressure sensor 3271 measures the air pressure which is the pressure of the fluid in the second port 327 immediately before the second pressure chamber 325. However, the first pressure sensor 3261 may be arranged anywhere as long as it can measure the air pressure between the switching valve 35 and the first pressure chamber 324. Also, the second pressure sensor 3271 may be arranged anywhere as long as it can measure the air pressure between the switching valve 35 and the second pressure chamber 325.

[0054] FIG. 7 is a control block diagram showing the control configuration of the NC lathe 1 shown in FIG. 1 according to the present invention.

[0055] As shown in FIG. 7, the NC lathe 1 includes 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 includes a plurality of buttons, keys, etc. for receiving input operations by the operator of the NC lathe 1. Note that the operation unit 11 may be a touch panel integrated with the display unit 12. The display unit 12 is a display for displaying various information regarding the NC lathe 1, such as NC programs, various setting values, error contents, and the estimation results of the estimation unit 23 described later.

[0056] The control device 2 includes a timer 21, a storage means 22, and an estimation unit 23. The timer 21 is used to measure the passage of time. The timer 21 measures, for example, the elapsed time since the power of the NC lathe 1 was turned on or the elapsed time since a predetermined operation was started.

[0057] The storage means 22 stores a control program, an NC program, various information, etc., and is composed of a non-volatile memory and a volatile memory. The storage means 22 includes a conversion information storage unit 221, a differential pressure information storage unit 222, and a set time storage unit 223.

[0058] The conversion information storage unit 221 shown in FIG. 7 is a functional part that stores the relationship between the gripping force of the workpiece W1 on the first spindle 4 and the effective differential pressure described above.

[0059] The differential pressure information storage unit 222 is a functional part that stores the differential pressure information between the first pressure measured by the first pressure sensor 3261 and the second pressure measured by the second pressure sensor 3271, together with the information on the elapsed time from a predetermined timing. Note that instead of the differential pressure information, the first pressure information and the second pressure information may be stored in the differential pressure information storage unit 222 together with the information on the elapsed time from a predetermined timing.

[0060] FIG. 8 is a graph showing the differential pressure generated when the state of the first spindle 4 shown in FIG. 1 changes from the gripping release state to the gripping state. In this FIG. 8, the time when a switching command from the gripping release state to the gripping state is issued in the setup operation or the NC program is set as 0 msec, and the differential pressure corresponding to the elapsed time from that time is shown. The differential pressure information storage unit 222 sequentially stores the differential pressure information shown in this graph as numerical information together with the time information. Hereinafter, the estimation operation of the gripping force will also be described with reference to FIG. 7 while referring to FIG. 8.

[0061] The set time memory unit 223 stores the time when an effective differential pressure is expected to occur when changing the state of the first main shaft 4 from the gripping release state to the gripping state by driving the air cylinder 32 (see FIG. 2). Specifically, based on the arrival signal generated when the end sensor 328 detects that the piston 322 (see FIG. 2) has moved to the most one side, it stores the time S1 (see FIG. 8) indicating how long before that time the effective differential pressure has occurred. This time S1 corresponds to an example of a predetermined time. The time S1 is approximately constant regardless of the magnitude of the gripping force as long as the shape of the cam surface 42a is the same. This is because after the effective differential pressure has occurred, the tip portion 43b (see FIG. 3) of the claw contacts the large-diameter surface 42a3 (see FIG. 3) with no change in diameter, so the movement of the rear end side of the shifter 42 is greatly affected by inertia, and the piston 322 moves to the most one side in approximately a constant time. In this embodiment, 50 msec is set as this time S1. This time S1 is set by the manufacturer of the NC lathe 1 through an operation test, but it may be made changeable by the operator's input.

[0062] When a switching command indicating a state change to the gripping state is issued, the control device 2 switches the switching valve 35 to supply air to the first pressure chamber 324 and exhaust the air in the second pressure chamber 325. Then, the control device 2 calculates the differential pressure obtained by subtracting the second pressure measured by the second pressure sensor 3271 from the first pressure measured by the first pressure sensor 3261, and sequentially stores the differential pressure information, which is the calculation result, in the differential pressure information storage unit 222 in association with the information on the elapsed time since the issuance of the switching command. In FIG. 8, in addition to the stored differential pressure information, the output signal of the end sensor 328 is shown. The signal indicated by the rising line upward among the output signals of the end sensor 328 becomes the arrival signal. FIG. 8 shows the differential pressure information from when the switching command is issued until after the arrival signal is received. Among the differential pressure information, the differential pressure information before time S1 from the storage time point may be deleted or overwritten from the differential pressure information storage unit 222. By doing so, the capacity of the storage means 22 can be reduced. As shown in FIG. 8, the differential pressure gradually increases from when the switching valve 35 is switched. When the tip end portion 43b reaches the boundary point between the changing surface 42a2 and the large-diameter surface 42a3, it becomes the effective differential pressure, which is the maximum value until then. After the tip end portion 43b exceeds the boundary point and temporarily decreases due to the reaction, it starts to rise again. In other words, the effective differential pressure can also be said to be the maximum value, which is a temporary peak of the differential pressure that occurs when the tip end portion 43b reaches the boundary point between the changing surface 42a2 and the large-diameter surface 42a3. After that, when the control device 2 receives the arrival signal, the differential pressure becomes a value slightly exceeding the above-mentioned maximum value (peak value).

[0063] When the control device 2 receives the arrival signal, the estimation unit 23 obtains the differential pressure at a time point S1 seconds before that time from the differential pressure information storage unit 222. Then, regarding this differential pressure as the effective differential pressure, the gripping force of the first main shaft 4 is estimated from the relationship between the gripping force stored in the conversion information storage unit 221 and the effective differential pressure. Further, the estimation unit 23 determines whether the effective differential pressure is within a predetermined range, and if it is not within the predetermined range, determines that there is an abnormal gripping force. The predetermined range of the effective differential pressure, which is the criterion for determining an abnormal gripping force, is a numerical range input by the operator using the operation unit 11 during the setup operation. However, this predetermined range may be set as a percentage such as ±30% with respect to the effective differential pressure adjusted during the setup operation. Also, a predetermined range may be set with a gripping force that is substantially synonymous with the predetermined range of the effective differential pressure.

[0064] The estimation unit 23 displays the estimated value of the gripping force and whether there is an abnormal gripping force on the display unit 12. However, the estimation unit 23 may display only the value of the gripping force. In this case, the determination of an abnormal gripping force may be omitted. Also, the estimation unit 23 may display that there is an abnormal gripping force only when there is an abnormal gripping force. The operation of this estimation unit 23 is executed each time the state changes to the gripping state during the setup operation and during machining. However, the operation of the estimation unit 23 may be executed only during the setup operation or only during machining. Also, the operator may be able to select whether to execute the operation of the estimation unit 23 in each of the setup operation and during machining. In addition, when the estimation unit 23 determines that there is an abnormal gripping force, the control device 2 may alarm-stop the operation of the NC lathe 1.

[0065] According to the NC lathe 1 of the present embodiment described above, since the gripping force of the collet chuck 48 is estimated based on the differential pressure between the first pressure and the second pressure, which is the driving force in the air cylinder 32 that reduces the diameter of the collet chuck 48 to grip the first spindle 4, the gripping force of the workpiece W1 can be estimated with high accuracy. Further, the gripping force can be estimated each time the workpiece W1 is gripped not only during the setup operation but also during machining such as continuous machining using an NC program. As a result, it is also possible to determine during machining an abnormal gripping force such as a decrease in the gripping force due to wear of the components constituting the collet opening and closing mechanism from the air cylinder 32 to the collet chuck 48 and its peripheral components. By determining the abnormal gripping force during machining, production defects can be suppressed, and thus the productivity of the NC lathe 1 is improved. In addition, by attaching the first pressure sensor 3261 and the second pressure sensor 3271 and adding or rewriting the control program of the control device 2, it can also be applied to the existing NC lathe 1.

[0066] Further, when the change in the differential pressure is gentle, such as when the gripping force is set weak, or due to external disturbance, it may be difficult to recognize the maximum value of the differential pressure that appears when the tip portion 43b reaches the boundary point between the changing surface 42a2 and the large-diameter surface 42a3. However, by regarding the differential pressure before the time S1 from the arrival signal as the effective differential pressure, the gripping force can be easily estimated even when the maximum value is difficult to recognize. Moreover, since there is no operation of extracting the maximum value, the calculation amount is small and the burden on the control device 2 is small.

[0067] Furthermore, since the abnormal gripping force is determined and displayed on the display unit 12, the operator can easily recognize whether the gripping force is abnormal.

[0068] Based on the above configurations of the first spindle headstock 3 and the first spindle 4, the collet opening and closing mechanism in the NC lathe 1 of the present embodiment has been described. However, the second spindle headstock 7 and the second spindle 8 are also provided with a collet opening and closing mechanism having the same configuration as that of the first spindle headstock 3 and the first spindle 4. Therefore, although the description is omitted, similar to the first spindle 4, the estimation unit 23 can estimate the gripping force of the machined workpiece W2 with high accuracy for the second spindle 8 as well. Moreover, since the second spindle 8 often grips the machined portion of the workpiece W1 machined by the first spindle 4 and the first tool post 6, by estimating the gripping force of the machined workpiece W2, it is also possible to detect a machining defect in the gripping portion of the machined workpiece W2 gripped by the second spindle 8. That is, if the gripping force of the machined workpiece W2 is significantly different from the desired gripping force, it can be determined that there is a machining defect in the gripping portion. Note that in the second spindle 8, the machined workpiece W2 corresponds to an example of the workpiece.

[0069] Subsequently, a modified example of the estimation unit 23 will be described. In the following description, components having the same names as the components described so far may be assigned the same reference numerals as those used so far, and duplicate descriptions may be omitted.

[0070] The estimation unit 23 of the modified example is different from the previous embodiment in that the maximum value of the differential pressure in a predetermined time range is used as the effective differential pressure to estimate the gripping force. In the set time storage unit 223 of the modified example, based on the time point when the end sensor 328 detects the arrival signal indicating that the piston 322 has moved to the most one side, a time range S2 (see FIG. 8) in which the effective differential pressure may occur before that time point is stored. The estimation unit 23 acquires the differential pressure information in the time range S2 from the differential pressure information storage unit 222, and estimates the gripping force based on the maximum value of the differential pressure in the time range S2. In this modified example, the time range S2 is set from 150 msec before the arrival signal to 20 msec before the arrival signal excluding the increase in the differential pressure immediately before the arrival signal. Note that the entire range from the time when the switching command to the gripping state is issued to 20 msec of the arrival signal may be set as the time range S2. Also, although this time range S2 is set by the manufacturer of the NC lathe 1, it may be made changeable by the input of the operator.

[0071] In this modification, since an operation of extracting the maximum value in the time range S2 occurs as compared with the previous embodiment, the burden on the control device 2 increases. Further, since it becomes necessary to store the differential pressure for a long time in the differential pressure information storage unit 222 as compared with the previous embodiment, it is necessary to provide the large-capacity storage means 22. However, in addition to the effects of the previous embodiment, there is an effect that the gripping force can be estimated more accurately by obtaining the maximum value in the time range S2.

[0072] The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope described in the claims. For example, in the description of the present embodiment, an example in which the present invention is applied to a so-called Swiss-type NC lathe 1 provided with the guide bush 5 has been shown. However, the present invention may be applied to other machine tools such as a lathe or a machining center not provided with the guide bush 5. Further, the second spindle headstock 7 and the second tool post 9 may be omitted. Furthermore, the conversion information storage unit 221 may store information on the relationship between the gripping force and the effective differential pressure for each characteristic such as the material and shape of the workpiece W1. In that case, the estimation unit 23 may select information corresponding to the characteristic of the workpiece W1 to be used from the information on the relationship between the gripping force and the effective differential pressure stored in the conversion information storage unit 221 and estimate the gripping force.

[0073] Note that even constituent elements included only in the description of each of the above-described modifications may be applied to other modifications.

Description of Reference Numerals

[0074] 1 NC lathe (machine tool) 4 First spindle (spindle) 23 Estimation unit 32 Air cylinder (fluid pressure cylinder) 48 Collet chuck (gripping portion) 322 Piston 324 First pressure chamber 325 Second pressure chamber 3261 First pressure sensor 3271 Second pressure sensor W1 Workpiece

Claims

1. It has a gripping part that grips the workpiece by reducing the diameter and releases the gripping of the workpiece by expanding the diameter, a spindle that rotates around the spindle center line as the rotation center, and It has a first pressure chamber and a second pressure chamber partitioned by a piston. By supplying fluid to the first pressure chamber, the piston is moved to one side to reduce the diameter of the gripping part. By supplying fluid to the second pressure chamber, the piston is moved to the other side to expand the diameter of the gripping part. A fluid pressure cylinder, A first pressure sensor that measures a first pressure, which is the pressure of the fluid supplied to the first pressure chamber when the piston is moved to the one side, A second pressure sensor that measures a second pressure, which is the pressure of the fluid flowing out from the second pressure chamber when the piston is moved to the one side, A machine tool characterized by comprising an estimation unit that estimates the gripping force of the gripping part based on the differential pressure between the first pressure measured by the first pressure sensor and the second pressure measured by the second pressure sensor.

2. The machine tool according to claim 1, wherein the estimation unit estimates the gripping force based on the differential pressure a predetermined time before the piston reaches the arrival point on the one side.

3. The machine tool according to claim 1, wherein the estimation unit estimates the gripping force based on the maximum value of the differential pressure in a predetermined time range before the piston reaches the arrival point on the one side.

4. The machine tool according to any one of claims 1 to 3, wherein the estimation unit determines whether the differential pressure is within a predetermined range, and if it exceeds the predetermined range, determines that there is an abnormality in the gripping force.

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