Misalignment detection method and device, and machine tool equipped with misalignment detection device

Abstract

This misalignment detection device (75) comprises: a reference current storage unit (76) that stores, as a reference current value, a drive current supplied to a drive motor (46a) when a rotary table is rotated about a first axis at a prescribed rotation velocity in a reference state in which a mounting surface is in a horizontal state and an object to be attached is not attached; and a misalignment detection unit (77). The misalignment detection unit (77) acquires, as an actual current value, a drive current supplied to the drive motor (46a) when the rotary table to which the object to be attached is attached on the mounting surface is tilted such that the mounting surface of the rotary table is at a prescribed angle relative to the horizontal plane, and the rotary table is rotated about the first axis at the prescribed rotation velocity in this tilted state. The misalignment detection unit (77) calculates a differential between the acquired actual current value and a reference current value stored in the reference current storage unit (76), and detects a misalignment state on the basis of the obtained differential value.

Description

[Technical Field]

[0001] The present invention relates to a method and device for detecting the degree of misalignment of an object placed on a rotary table with respect to the rotary table, and to a machine tool equipped with this device. [Background technology]

[0002] For example, one method for detecting misalignment, defined as the deviation between the axis of inertia including the center of gravity of a rotating material and its axis of rotation, is disclosed in Japanese Patent Laid-Open Publication No. 2004-138423. This method not only detects misalignment but also detects imbalance, which is the distribution of inertial mass at each rotation angle. More specifically, the rotating material is held on a rotary table supported by a spindle so that its rotation axis coincides with the rotation axis of the spindle, and the spindle is then rotated by a motor. The amount of vibration in the direction perpendicular to the axis at each rotation angle of the spindle is detected to measure the unbalance of the rotating material.

[0003] However, the conventional unbalance detection methods described above are designed to detect imbalance in rotating material such as cast products, which do not have their own balance, and therefore have low detection accuracy. Therefore, when a processed product (object to be placed) that has been machined with a certain degree of precision and has a certain degree of balance itself is placed on a rotary table, the above-mentioned unbalance detection methods are unable to detect with sufficient accuracy the misalignment of the object to be placed on the rotary table, including the accuracy of its attachment to the rotary table, i.e., the degree of misalignment of the center of gravity (axis of inertia) of the object to be placed on the rotary table's central axis of rotation.

[0004] Therefore, in the field of machine tools equipped with a rotary table, misalignment has conventionally been detected as follows: First, a workpiece (object to be placed) is placed and fixed on the rotary table, and then the motor for the rotary table is driven to rotate the rotary table at a constant rotational speed, and the current value (equivalent to torque value) supplied to the motor by feedback control is detected. The detected current value (actual current value) is then compared with a reference current value, thereby detecting the misalignment between the axis of the attached workpiece and the axis of the rotary table.

[0005] The reference current value is, for example, a current value (equivalent to a torque value) supplied to the motor when the rotary table is rotated at a constant, predetermined rotational speed by the motor, with nothing attached to the rotary table as the reference state, and is a current value corresponding to the rotation phase of the rotary table.

[0006] Then, when the target workpiece is attached to the rotary table and rotated, the difference between the actual current value supplied to the motor and the reference current value is calculated, and the misalignment state is estimated from the calculated difference. That is, if the axis of the workpiece and the axis of the rotary table are not misaligned, the difference value is close to "0," and if there is misalignment, the difference value increases depending on the magnitude of the misalignment. Therefore, the difference between the actual current value and the reference current value can be calculated, and the misalignment state can be estimated from the difference value.

[0007] In this way, by detecting the misalignment of the workpiece relative to the rotary table, if it is deemed that the misalignment exceeds the tolerance range, measures can be taken such as slowing down the acceleration and deceleration by reducing the time constant when rotating the rotary table, or setting a limit on the rotation speed of the rotary table. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-138423 Summary of the Invention [Problem to be solved by the invention]

[0009] However, even in the method of detecting the misalignment state of the target workpiece based on the value of the current supplied to the motor, there are still some points to be improved, as will be explained below.

[0010] In other words, in the case of a motor with a small output, the fluctuation component of the current value caused by misalignment of the target workpiece is large compared to the current value supplied to the motor, making it relatively easy to detect the misalignment state, but in the case of a motor with a large output, the fluctuation component of the current value caused by misalignment of the target workpiece is small compared to the current value supplied to the motor, making it difficult to detect the misalignment state.

[0011] Furthermore, when the weight of the target workpiece attached to the rotary table is light compared to the weight of the rotary table, the fluctuation component of the current value caused by the misalignment of the target workpiece becomes small, making it difficult to detect the misalignment state.

[0012] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a misalignment detection method and device that can detect misalignment conditions, including attachment errors of an object to be mounted on a rotary table, more remarkably than ever before, even when the object mounted on the rotary table is a machined workpiece, and a machine tool equipped with this misalignment detection device. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention particularly relates to a misalignment detection method and misalignment detection device that are suitably implemented in an apparatus, such as a machine tool, that has a flat support surface on which a support object including an attachment target is placed, a rotary table that rotates around a first axis perpendicular to the support surface and rotates around a second axis parallel to the support surface, and a drive motor that rotates the rotary table.

[0014] The misalignment detection method according to the present invention is a method for detecting a degree of misalignment of a center of gravity position of the object placed on the mounting surface of the rotary table with respect to the first axis in the device, the method comprising: a reference current acquisition step of acquiring, as a reference current value, a drive current supplied to a drive motor when the rotary table is rotated around the first axis at a predetermined rotation speed in a reference state in which the mounting surface is horizontal and the mounting object is not attached; an actual current acquisition step of, after the object to be attached to the turntable, rotating and tilting the turntable about the second axis so that the placement surface of the turntable forms a predetermined angle with respect to a horizontal plane, and acquiring, as an actual current value, a drive current supplied to the drive motor when the turntable is rotated about the first axis at the rotation speed after this attitude change; and a misalignment detection step of calculating a difference between the actual current value and a reference current value and detecting the degree of misalignment based on the calculated difference.

[0015] In this misalignment detection method, first, in the reference current acquisition process, in a reference state in which the mounting surface is horizontal and no object is attached, the drive current value corresponding to the phase supplied to the drive motor when the rotary table is rotated at a predetermined rotational speed around the first axis is acquired as a reference current value.

[0016] When the turntable is not tilted, i.e., when the mounting surface is horizontal, and the turntable is rotated around the first axis, a load corresponding to the inertia of the turntable with no object attached acts on the drive motor at the beginning of rotation (during acceleration). In contrast, once the turntable reaches a constant speed, the drive motor is not subjected to a significant load unless an external force is applied, and the drive current supplied to the drive motor remains stable. In the reference current acquisition step, a drive current value corresponding to the phase of the drive motor is acquired when the turntable is rotated in a reference state with no object attached.

[0017] In addition, in the actual current acquisition process, after the object to be mounted is mounted on the rotary table, the rotary table is rotated and tilted around the second axis so that its mounting surface is at a predetermined angle with respect to the horizontal plane, and the drive motor is driven in the tilted state after this attitude change to rotate the rotary table around the first axis at the rotational speed, and the drive current value corresponding to the phase supplied to the drive motor is acquired as the actual current value.

[0018] When a turntable with an object attached to it is rotated around the first axis while tilted and rotated a predetermined angle around the second axis, a load corresponding to the inertia of the turntable and the object acts at the beginning of rotation (acceleration), as described above. When the turntable reaches a constant speed, if the object is misaligned with the turntable, i.e., if the center of gravity of the object is not on the rotation axis of the turntable but is offset from the rotation axis, the drive motor is subjected to a load consisting of a centrifugal force related to the mass of the object depending on the amount of misalignment and a component related to the gravity of the object depending on the amount of misalignment and the tilt of the object. Therefore, the actual current value obtained in this actual current acquisition process includes a variable component corresponding to the centrifugal force associated with the rotation of the object and the gravity of the object.

[0019] When misalignment occurs, the component related to the gravity of the object acts as torque on the drive motor according to the amount of misalignment, and varies depending on the rotational phase of the drive motor. For example, if the phase at which the center of gravity of the object is located directly below the rotational axis of the turntable is 0°, and the center of gravity of the object rotates counterclockwise around the rotational axis of the turntable as the turntable rotates counterclockwise, when the counterclockwise rotational phase is 0°, downward gravity acts on the drive motor but no torque is applied. When the rotational phase exceeds 0°, a gravity component acts in the opposite direction to the rotational direction, and a reverse torque (positive torque) corresponding to the gravity component begins to act on the drive motor, reaching its maximum when the rotational phase is 90°. This positive torque acts in a direction that increases the load on the drive motor, and when the rotational phase is 90°, the torque acting as a load on the drive motor is at its maximum.

[0020] Next, when the rotation phase exceeds 90°, the torque in the reverse direction (positive torque) gradually decreases, and when the phase reaches 180°, the torque becomes "0," and only downward gravity acts on the drive motor. When the rotation phase exceeds 180°, a gravity component in the same direction as the rotation direction (forward direction) acts, and a forward torque (negative torque) corresponding to the gravity component begins to act on the drive motor, and when the rotation phase is 270°, the forward torque becomes maximum. This forward torque, or negative torque, acts in a direction that relieves the load on the drive motor, and therefore, when the rotation phase is 270°, the torque acting as a load on the drive motor is minimum. When the rotation phase exceeds 270°, the forward torque (negative torque) gradually decreases, and when the rotation phase reaches 0°, the torque becomes "0," and only downward gravity acts on the drive motor. On the other hand, when there is no misalignment, the component related to the gravity of the placed object acts on the drive motor at a constant value, but does not act as torque.

[0021] Next, in the misalignment detection process, the difference between the actual current value and the reference current value is calculated, and the degree of misalignment is detected based on the calculated difference value. The greater the amount of misalignment, the larger the difference value. Therefore, the magnitude of misalignment, i.e., the degree of misalignment, can be estimated (detected) from the magnitude of the difference value. Furthermore, the difference value between the actual current value and the reference current value corresponding to the phase of the drive motor is calculated, and the degree of misalignment can be estimated from the difference between its maximum and minimum values. That is, if the axis of the object and the axis of the rotary table (rotation center axis) are not misaligned, the difference value does not fluctuate significantly. However, if the axis of the object (including the center of gravity) and the axis of the rotary table are misaligned, as described above, the value will include fluctuation components corresponding to the centrifugal force associated with the rotation of the object and the gravity of the object. The component related to the gravity of the object acts as a torque on the drive motor and varies depending on the rotation phase of the drive motor. Therefore, the difference value fluctuates depending on the magnitude of the misalignment and the rotation phase of the drive motor. Therefore, by calculating the difference between the actual current value and the reference current value corresponding to the phase of the drive motor, the magnitude (degree) of misalignment can be estimated from the difference between the maximum and minimum values.

[0022] In this way, this misalignment detection method estimates the misalignment state from the difference between the actual current value and the reference current value when the rotating table with the object attached to it is rotated in a tilted state.Therefore, even if the object attached to the rotating table is machined, the degree of misalignment of the object relative to the rotating table can be detected more significantly than in the past.

[0023] That is, as described above, when a turntable with an object attached thereto is rotated while tilted, if the object is misaligned with respect to the turntable, the drive motor is subjected to a load consisting of a centrifugal force corresponding to the amount of misalignment caused by the rotation of the object, and a component corresponding to the amount of misalignment caused by the gravity of the object and the inclination of the object. Therefore, the actual current value obtained in this actual current acquisition process is a value that includes a fluctuating component corresponding to the centrifugal force caused by the rotation of the object and the gravity of the object.

[0024] On the other hand, if the turntable with the object attached is rotated without tilting it, as in the conventional case, and the object is misaligned with the turntable, only the centrifugal force caused by the rotation of the object acts on the drive motor as a load. Therefore, the current value supplied to the drive motor in this state contains a variable component corresponding only to the centrifugal force caused by the rotation of the object.

[0025] As described above, in conventional methods, the difference value between the actual current value and the reference current value reflects only the fluctuation component corresponding to the centrifugal force generated by the misalignment. However, in the misalignment detection method of the present invention, the difference value between the actual current value and the reference current value includes not only the fluctuation component corresponding to the centrifugal force generated by the misalignment, but also a fluctuation component corresponding to the gravity of the object placed on the rotating table, so that the degree of misalignment of the object placed on the rotating table can be detected more remarkably than in conventional methods.

[0026] Thus, the misalignment detection method according to the present invention makes it possible to detect the degree of misalignment of an object relative to the turntable with sufficient accuracy, even if the object is machined with a certain degree of precision and has a certain degree of balance. Furthermore, the misalignment state of the object relative to the turntable can be detected more reliably regardless of the magnitude of the drive motor output and regardless of the weight of the object.

[0027] For example, in the case where a workpiece is directly attached to a rotary table, the workpiece corresponds to the object to be mounted, and the workpiece also corresponds to the object to be mounted. Also, in the case where a workpiece is mounted to a mounting jig attached to a rotary table, the mounting jig and the workpiece correspond to the object to be mounted, and the workpiece corresponds to the object to be mounted. Also, in the case where the mounting jig with the workpiece attached is mounted on the rotary table, the mounting jig and the workpiece correspond to the object to be mounted, and also correspond to the object to be mounted.

[0028] Furthermore, a misalignment detection device according to the present invention is a device that can suitably implement the above-described misalignment detection method, that is, for example, a device that detects the degree of misalignment of the center of gravity position of an object placed on the placing surface of the rotary table in the machine tool, with respect to the first axis, and a reference current storage unit that stores, as a reference current value, a drive current supplied to a drive motor when the table is rotated around the first axis at a predetermined rotation speed in a reference state in which the mounting surface is horizontal and the mounting object is not attached; and a misalignment detection unit that acquires, as an actual current value, a drive current supplied to the drive motor when the rotary table, on which the object to be attached is attached, is rotated around the second axis so that the mounting surface is at a predetermined angle with respect to a horizontal plane, and that calculates a difference between the acquired actual current value and the reference current value stored in the reference current memory unit and detects the degree of misalignment based on the acquired difference value, in a state after the attitude change in which the rotary table, on which the object to be attached is attached, is rotated around the second axis so that the mounting surface is at a predetermined angle with respect to a horizontal plane.

[0029] According to this misalignment detection device, the reference current value obtained in the same manner as in the above-described reference current obtaining step is stored in advance in the reference current storage unit.

[0030] Then, after the object to be attached is attached to the rotating table, in the same manner as in the above-mentioned actual current acquisition process and misalignment detection process, the rotating table is rotated and tilted around the second axis so that its mounting surface is at a predetermined angle with respect to the horizontal plane (state after posture change), and the drive current supplied to the drive motor when rotated around the first axis at the rotational speed is acquired as an actual current value by the misalignment detection unit, and the difference between the acquired actual current value and the reference current value stored in the reference current memory unit is calculated, and the degree of misalignment is detected based on the calculated difference value.

[0031] With this misalignment detection device, the difference between the actual current value and the reference current value contains a fluctuation component corresponding to the gravity of the object to be placed on it, in addition to a fluctuation component corresponding to the centrifugal force caused by the misalignment, so that the misalignment state of the object to be placed on the turntable can be detected more reliably than in the past. Thus, with this misalignment detection device, the degree of misalignment of the object to be placed on the turntable can be detected with sufficient accuracy, even if the object to be placed on the turntable is a machined product that has been machined with a certain degree of precision and is itself somewhat balanced. Furthermore, the misalignment state of the object to be placed on the turntable can be detected more reliably regardless of the output of the drive motor and regardless of the weight of the object to be placed on the turntable.

[0032] Furthermore, in the above-described misalignment detection method and misalignment detection device, the turntable is preferably tilted about the second axis so that the mounting surface thereof forms an angle in the range of 15° to 90° with respect to the horizontal plane, more preferably at an angle in the range of 30° to 90°, still more preferably at an angle in the range of 45° to 90°, and most preferably at an angle in the range of 60° to 90°. Note that in the present invention, the tilted positions of the turntable also include a position in which the turntable is rotated so that the mounting surface thereof forms an angle of 90° with respect to the horizontal plane.

[0033] The present invention also relates to a machine tool equipped with the above-mentioned misalignment detection device. With this machine tool, when a target object is attached and a predetermined machining operation is performed, if the misalignment of the object relative to the table exceeds a predetermined standard, the time constant for rotating the table can be reduced to slow down acceleration and deceleration, or a limit can be placed on the rotation speed of the table. [Effects of the Invention]

[0034] As described above, according to the present invention, compared to the prior art, it is possible to detect the degree of misalignment of an object with respect to a turntable with sufficient accuracy, even if the object is machined with a certain degree of precision and is itself a workpiece that has a certain degree of balance. Furthermore, it is possible to more reliably detect the misalignment of an object placed on the turntable with respect to the turntable, regardless of the magnitude of the drive motor output, and it is also possible to more reliably detect the misalignment regardless of the weight of the object. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a perspective view showing a machine tool according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of a control device according to the present embodiment. [Figure 3] FIG. 2 is a side view showing a rotary table portion of the machine tool according to the embodiment. [Figure 4] FIG. 2 is a front view showing a rotary table portion of the machine tool according to the embodiment. [Figure 5] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 6] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 7] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 8] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 9] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 10] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 11] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 12] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 13]1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 14] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 15] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 16] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 17] 1A and 1B are explanatory diagrams for explaining a misalignment detection method according to the present embodiment. [Figure 18] FIG. 10 is an explanatory diagram for explaining a modified example of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0036] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0037] [Outline of machine tool configuration] First, the schematic configuration of a machine tool according to one embodiment of the present invention will be described. As shown in Figures 1 and 2, the machine tool 1 of this example is composed of a bed 2, a first saddle 7 and a swing table mechanism 20 disposed on the bed 2, a second saddle 8 disposed on the first saddle 7, a spindle head 9 disposed on the second saddle 8, and a control device 50.

[0038] The bed 2 comprises a base 3 formed in a rectangular shape when viewed from above, two side walls 4 and 5 erected on both the left and right sides of the base 3 so as to face each other, and a rear wall 6 erected between the side walls 4 and 5 at the rear side of the base 3 so as to connect to them.

[0039] The first saddle 7 is a frame having a rectangular shape in a plan view, and is disposed on the side walls 4, 5 of the bed 2 so as to span them, and is movable in the direction of the arrow Y axis, which is a feed axis in the horizontal front-to-rear direction, by Y-axis guide mechanisms 30, 31 disposed on the upper surfaces of the side walls 4, 5, respectively, and is driven by Y-axis drive mechanisms 32, 33 also disposed on the upper surfaces of the side walls 4, 5, respectively, to move in the Y axis direction. The Y-axis drive mechanisms 32, 33 are equipped with Y drive motors 32a, 33a, respectively.

[0040] The second saddle 8 is disposed so as to penetrate within the frame of the first saddle 7, and is movable in the X-axis direction, which is a horizontal feed axis perpendicular to the Y-axis, by X-axis guide mechanisms 35 and 36 provided on both sides of the first saddle 7 along the X-axis indicated by the arrow, and is driven by an X-axis drive mechanism 37 also disposed on the first saddle 7 to move in the X-axis direction. This X-axis drive mechanism 37 is equipped with an X-axis drive motor 37a.

[0041] The spindle head 9 is held by the second saddle 8 by a Z-axis guide mechanism (not shown) disposed on the second saddle 8 so as to be movable in the Z-axis direction, which is a feed axis perpendicular to the X-axis and Y-axis, and is driven by Z-axis drive mechanisms 40, 41 disposed on both sides thereof to move in the Z-axis direction. These Z-axis drive mechanisms 40, 41 are equipped with Z-axis drive motors 40a, 41a, respectively. The spindle head 9 is provided with a spindle 10 extending downward from its lower end, and a tool T is attached to the lower end of the spindle 10. The spindle 10 is held by the spindle head 9 so as to be rotatable about its axis, and is rotated about its axis by a spindle motor 48.

[0042] The oscillating table mechanism 20 includes a table base 21 that is L-shaped when viewed from the left side, and a rotary table 24 provided on a horizontal portion 22 of the table base 21. The vertical portion 23 of the table base 21 is held on the rear wall 6 of the bed 2 so as to be rotatable (pivotable) about a rotation axis A1 that is parallel to the Y axis in the direction of the arrow B axis, which is a rotary feed axis, and is driven by a B axis drive mechanism 45 that has a B axis drive motor 45a to pivot in the B axis direction. The rotation axis A1 corresponds to the second axis.

[0043] A rotary table 24 is disposed on the horizontal portion 22 of the table base 21, and is held by the horizontal portion 22 so as to be rotatable in the direction of the arrow C axis, which is a rotary feed axis, around a rotation axis A2 that is parallel to the Z axis and perpendicular to the upper surface of the rotary table 24, and is driven by a C-axis drive mechanism 47 having a C-axis drive motor 47a to rotate in the C-axis direction. The rotation axis A2 corresponds to the first axis.

[0044] The operations of the feed axis drive motors, namely, the X-axis drive motor 37a, the Y-axis drive motors 32a, 33a, the Z-axis drive motors 40a, 41a, the B-axis drive motor 45a, and the C-axis drive motor 47a, as well as the spindle motor 48 that drives the spindle 10, are controlled by the control device 50.

[0045] The control device 50 is composed of a numerical control device 51, a feed axis drive unit 65, a main axis drive unit 72, and a misalignment detection device 75, and an input / output device 80 is connected to the numerical control device 51 and the misalignment detection device 75.

[0046] The numerical controller 51 includes an NC program storage unit 52, a program analysis unit 53, a feed axis control unit 55, and a spindle control unit 62, and the misalignment detection device 75 includes a reference current storage unit 76 and a misalignment detection unit 77. The numerical controller 51 and the misalignment detection device 75 are configured by a computer including a CPU, RAM, ROM, etc., and the program analysis unit 53, feed axis control unit 55, spindle control unit 62, and misalignment detection unit 77 have their functions realized by computer programs and execute the processes described below. The NC program storage unit 52 and reference current storage unit 76 are configured by appropriate storage media such as RAM.

[0047] The NC program storage unit 52 is a functional unit that stores an NC program for NC control, for example, a machining program, and stores an NC program input from the input / output device 80, for example.

[0048] The program analysis unit 53 sequentially reads out the NC programs to be executed from the NC programs stored in the NC program storage unit 52, one by one for each block that constitutes the NC program, processes the NC code contained in the block, and when processing the NC code related to the feed control of each feed axis, sends a command related to the NC code to the feed axis control unit 55, and when processing the NC code related to the rotation control of the spindle 10, sends a command related to the NC code to the spindle control unit 62.

[0049] The feed axis control unit 55 includes a B-axis control unit 56, a C-axis control unit 57, an X-axis control unit 58, a Y-axis control unit 59, and a Z-axis control unit 60, and transmits a control signal corresponding to a command related to the NC code transmitted from the program analysis unit 53 to the feed axis drive unit 65. The feed axis drive unit 65 is an amplifier, and supplies a drive current corresponding to the received control signal to the corresponding feed axis drive motor. The feed axis drive unit 65 is composed of a B-axis drive unit 66, a C-axis drive unit 67, an X-axis drive unit 68, a Y-axis drive unit 69, and a Z-axis drive unit 70.

[0050] More specifically, the B-axis control unit 56 receives a command related to the B-axis from the program analysis unit 53 and transmits a corresponding control signal to the B-axis drive unit 66, and the B-axis drive unit 66 supplies a drive current corresponding to the received control signal to the B-axis drive motor 45a to rotate the B-axis drive motor 45a. The C-axis control unit 57 receives a command related to the C-axis from the program analysis unit 53 and transmits a corresponding control signal to the C-axis drive unit 67, and the C-axis drive unit 67 supplies a drive current corresponding to the received control signal to the C-axis drive motor 46a to rotate the B-axis drive motor 45a.

[0051] The X-axis control unit 58 receives commands related to the X-axis from the program analysis unit 53 and transmits a corresponding control signal to the X-axis drive unit 68. The X-axis drive unit 68 then supplies a drive current corresponding to the received control signal to the X-axis drive motor 37a to rotate the X-axis drive motor 37a. The Y-axis control unit 59 receives commands related to the Y-axis from the program analysis unit 53 and transmits a corresponding control signal to the Y-axis drive unit 69. The Y-axis drive unit 69 then supplies a drive current corresponding to the received control signal to the Y-axis drive motors 32a and 33a to rotate the Y-axis drive motors 32a and 33a. The Z-axis control unit 60 receives commands related to the Z-axis from the program analysis unit 53 and transmits a corresponding control signal to the Z-axis drive unit 70. The Z-axis drive unit 70 then supplies a drive current corresponding to the received control signal to the Z-axis drive motors 40a and 41a to rotate the Z-axis drive motors 40a and 41a.

[0052] Furthermore, when the spindle control unit 62 receives a command related to the rotation control of the spindle 10 from the program analysis unit 53, it transmits a corresponding control signal to a spindle drive unit 72. This spindle drive unit 72 is an amplifier, and supplies a drive current corresponding to the control signal received from the spindle control unit 62 to the spindle motor 48, thereby rotating the spindle motor 48.

[0053] In the machine tool 1 of this example having the above configuration, under the control of a numerical control device 51, the tool attached to the spindle 10 and the workpiece W placed on and fixed to the rotary table 24 are moved relatively in the X-, Y-, and Z-axis directions, which are three orthogonal feed axes, by the X-axis drive mechanism 37, the Y-axis drive mechanisms 32 and 33, and the Z-axis drive mechanisms 40 and 41. The rotary table 24 is driven by the B-axis drive mechanism 45 to turn in the B-axis direction, which is the rotary feed axis, and is driven by the C-axis drive mechanism 47 to rotate in the C-axis direction, which is the rotary feed axis.

[0054] Then, the tool T attached to the spindle 10 and the workpiece W placed on and fixed to the table 24 are moved relatively in the X-axis, Y-axis, Z-axis, B-axis, and C-axis directions by the X-axis drive mechanism 37, Y-axis drive mechanisms 32, 33, Z-axis drive mechanisms 40, 41, B-axis drive mechanism 45, and C-axis drive mechanism 47, whereby the workpiece W on the table 24 is machined by the tool T.

[0055] As indicated by the dashed arrow in FIG. 2, an NC code can be input from the input device 80 to the program analysis unit 53 via MDI (Manual Data Input). By inputting the NC code to the program analysis unit 53 via this MDI, the feed axis drive motors and the spindle motor 48 are driven via the feed axis drive unit 65 and the spindle drive unit 72 under the control of the program analysis unit 53, the feed axis control unit 55, and the spindle control unit 62.

[0056] Furthermore, manual operation signals are input from the input device 80 to the feed axis control unit 55 and the spindle control unit 62, and under the control of the feed axis control unit 55 and the spindle control unit 62, the feed axis drive motors and the spindle motor 48 are driven via the feed axis drive unit 65 and the spindle drive unit 72 in accordance with the manual operation signals.

[0057] The misalignment detection device 75 comprises a reference current storage unit 76 and a misalignment detection unit 77 .

[0058] The reference current storage unit 76 is a functional unit that stores a reference current value, which is a current value supplied from the C-axis drive unit 67 to the C-axis drive motor 46a. This reference current value is acquired as a drive current value corresponding to the rotation phase supplied to the C-axis drive motor 46a when the turntable 24 is rotated around the rotation axis A2 at a predetermined rotation speed under the control of the C-axis control unit 57 when the turntable 24 is in a reference state in which its upper surface (mounting surface) is horizontal and no object to be mounted, such as the workpiece W shown in FIG. 1 in this example, is mounted. In this example, the workpiece W also corresponds to the mounted object.

[0059] The rotational operation of the turntable 24 in the reference state (operation to acquire the reference current value) can be achieved manually, that is, by a manual operation signal input by an operator from the input / output device 80. For example, operation signals related to the B and C axes are input from the input / output device 80 to the feed axis control unit 55, and under the control of the B axis control unit 56 and the C axis control unit 57, the B axis drive motor 45a and the C axis drive motor 46a are driven via the B axis drive unit 66 and the C axis drive unit 67 of the feed axis drive unit 65, so that the table 24 is rotated in the B axis direction to make its upper surface horizontal, and then rotated at a predetermined rotation speed around the rotation axis A2.

[0060] At this time, the current value supplied from the C-axis drive unit 67 to the C-axis drive motor 46a is transmitted to the input / output device 80 as a reference current value and displayed on the input / output device 80. The operator inputs the reference current value displayed on the input / output device 80 from the input / output device 80 and stores it in the reference current value memory unit 76. Note that when inputting a manual operation signal from the input / output device 80, a mode can be adopted in which the manual operation signal (operation signals for the B and C axes) is input by specifying the reference operation mode. In this case, a mode can be adopted in which the reference current value is transmitted directly from the feed axis drive unit 65 to the reference current memory unit 76 and stored therein, without going through the input / output device 80 (see the transmission path indicated by the dashed arrow in FIG. 2).

[0061] After the object to be mounted, in this example the workpiece W, is mounted on the rotating table 24, the rotating table 24 is rotated (pivoted) about the rotation axis A1 and tilted so that its upper surface is at a predetermined angle with respect to the horizontal plane, and when the rotating table 24 is rotated at the predetermined rotation speed about the rotation axis A2 in this tilted state, the misalignment detection unit 77 acquires, as an actual current value, the current value corresponding to the rotation phase supplied to the C-axis drive motor 46a from the C drive control unit 67, calculates the difference between the acquired actual current value and the reference current value stored in the reference current memory unit 76, and detects the degree of misalignment based on the obtained difference value.

[0062] Next, the misalignment detection process performed by the misalignment detection device 75 in the machine tool 1 having the above-described configuration will be described.

[0063] First, as described above, under the control of the B-axis control unit 56 and the C-axis control unit 57, the B-axis drive motor 54a and the C-axis drive motor 46a are driven via the B-axis drive unit 66 and the C-axis drive unit 67 to rotate the table 24 in the B-axis direction until its upper surface is horizontal, and then rotate the table 24 in the C-axis direction at the predetermined rotation speed. The current value supplied from the C-axis drive unit 67 to the C-axis drive motor 46a at this time is acquired as a reference current value, and the acquired reference current value is stored in the reference current value storage unit 76. An example of the waveform of the current value obtained at this time according to the rotational phase of the turntable 24 is shown in FIG. 12. The rotational phase of 0° is an appropriately determined home position, and is defined, for example, as the rotational phase described below. Note that the waveforms shown in FIG. 12 are merely conceptual for purposes of illustrating this embodiment and do not represent actual waveform values.

[0064] Next, as described above, after the workpiece W, for example, is attached to the turntable 24, the B-axis drive motor 54a is driven via the B-axis drive unit 66 under the control of the B-axis control unit 56 to rotate (pivot) the turntable 24 in the B-axis direction so that its upper surface is tilted at a predetermined angle with respect to the horizontal, for example, at 90° (in the present invention, a 90° angle is also included in the tilted position) (see FIG. 5 ). Then, under the control of the C-axis control unit 57, the C-axis drive motor 46a is driven via the C-axis drive unit 67 to rotate the turntable 24 in the C-axis direction at the predetermined rotation speed. The misalignment detection unit 77 then acquires the value of the current supplied to the C-axis drive motor 46a from the C-axis drive unit 67 as an actual current value, calculates the difference between the acquired actual current value and the reference current value stored in the reference current storage unit 76, and detects the degree of misalignment based on the obtained difference. For example, if the difference value is greater than a theoretically or empirically determined threshold value, it is determined that there is misalignment that requires some kind of action.

[0065] Next, the principle of detecting the degree of misalignment will be explained below. First, when the turntable 24 with the workpiece W attached is viewed with its upper surface horizontal, if the workpiece W is attached misaligned with respect to the turntable 24, when the turntable 24 is rotated a predetermined number of times (one or more) at the predetermined rotation speed in the C-axis direction, as shown in FIG. 6, the C-axis drive motor 46a is subjected to a centrifugal force (=mv 2 / r) acts, where m is the mass of the workpiece W, v is the rotational speed of the workpiece W, and r is the radial misalignment of the central axis W1, which includes the center of gravity of the workpiece W, with respect to the rotation axis A2 of the turntable 24. Therefore, in this state, the waveform of the actual current value corresponding to the rotation phase of the turntable 24 and supplied from the C-axis drive unit 67 to the C-axis drive motor 46a is a waveform shifted in the direction in which the current value increases by an amount corresponding to the centrifugal force relative to the reference current value (see FIG. 13). The difference between the actual current value and the reference current value in this state is a value corresponding to the centrifugal force, and the greater the amount of misalignment, the greater the value, and becomes an approximately constant value as shown in FIG. 14.

[0066] On the other hand, when the workpiece W is mounted with its central axis W1 misaligned with the rotation axis A2 of the rotary table 24, if the rotary table 24 is tilted 90° in the B-axis direction and then rotated a predetermined number of times in the C-axis direction at the predetermined rotation speed, as shown in FIG. 7, the C-axis drive motor 46a will be subjected to a centrifugal force (=mv 2 In addition to the force (r / r), the gravity (= mg) of the workpiece W acts as a torque (see also Figures 8 to 11). As shown in Figures 8 to 11, when the rotational phase of the turntable 24 is 0° and the center of gravity of the workpiece W is located directly below the rotation axis A2 of the turntable 24, the turntable 24 is rotated counterclockwise (in the direction of the arrow) and the workpiece W rotates counterclockwise around the rotation axis A2. When the rotational phase is 0°, downward gravity acts on the C-axis drive motor 46a but no torque is acting (see Figure 8). When the rotational phase exceeds 0°, a gravity component acts in the opposite direction to the rotational direction, and a torque in the opposite direction (positive torque) corresponding to the gravity component begins to act on the C-axis drive motor 46a, and this torque reaches a maximum when the rotational phase is 90° (see Figure 9). This positive torque acts in a direction that increases the load on the C-axis drive motor 46a, and when this rotation phase is 90°, the torque acting as a load on the C-axis drive motor 46a is at its maximum.

[0067] When the rotation phase exceeds π / 2 (=90°), the torque in the reverse direction (positive torque) gradually decreases. When the rotation phase reaches π (=180°), the torque becomes zero, and only downward gravity acts on the C-axis drive motor 46a (see FIG. 10). Next, when the rotation phase exceeds π (=180°), a gravity component acts in the same direction as the rotation direction (forward direction), and a forward torque (negative torque) corresponding to the gravity component begins to act on the C-axis drive motor 46a, reaching a maximum when the rotation phase is 3π / 2 (=270°) (see FIG. 11). This forward torque, or negative torque, acts to reduce the load on the C-axis drive motor 46a. Therefore, when the rotation phase is 3π / 2 (=270°), the torque acting as a load on the C-axis drive motor 46a is minimized. Then, when the rotational phase exceeds 3π / 2 (=270°), the forward torque (negative torque) gradually decreases, and when the rotational phase reaches 0°, the torque becomes "0", and only downward gravity acts on the drive motor (see Figure 8).

[0068] Therefore, the actual current value corresponding to the rotation phase of the rotary table 24, which is supplied from the C-axis drive unit 67 to the C-axis drive motor 46a, is calculated by multiplying the reference current value by the centrifugal force (=mv 2 / r) and a current value resulting from torque corresponding to the gravity (= mg) of the workpiece W. An example of such a waveform of an actual current value is shown in FIG. 15. In FIG. 15, the solid line is the waveform of the reference current value, and the dashed line is the waveform of the actual current value. Furthermore, the waveform shown in FIG. 15, like the waveform shown in FIG. 12, is merely conceptual for explaining this embodiment, and does not represent the waveform of an actual value.

[0069] In this state, that is, when the turntable 24 is tilted by 90°, the difference between the actual current value and the reference current value when the workpiece W is attached misaligned with respect to the turntable 24 is due to the centrifugal force and torque, as described above, and the greater the amount of misalignment, the greater the value becomes, and the waveform of this difference value becomes, for example, a waveform such as that shown in Fig. 16. The waveform shown in Fig. 16 is a waveform that shows the difference between the actual current value and the reference current value shown in Fig. 15.

[0070] The misalignment detection unit 77 compares the difference value thus obtained with a predetermined threshold value, and if the difference value is greater than the threshold value, determines that the misalignment requires some kind of action (see Figure 16).

[0071] As described above in detail, the misalignment detection device 75 of this embodiment can detect the misalignment state of the workpiece W with respect to the rotary table 24 more remarkably than conventional devices.

[0072] That is, as described above, according to the conventional misalignment detection method, the rotary table 24 with the workpiece W attached thereto is rotated in the C-axis direction at the predetermined rotational speed with its upper surface horizontal. Therefore, if the workpiece W is attached misaligned with respect to the table 24, a centrifugal force corresponding to the mass of the workpiece W acts on the C-axis drive motor 46a, and the actual current value supplied from the C-axis drive unit 67 to the C-axis drive motor 46a is the reference current value plus a current value corresponding to the centrifugal force as a variable component.

[0073] On the other hand, according to the detection method of this embodiment, the rotary table 24 on which the workpiece W is attached is rotated in the B-axis direction so that its upper surface is tilted at a predetermined angle, 90° in this example, with respect to the horizontal plane, and then the table 24 is rotated in the C-axis direction at a predetermined rotational speed, so that if the workpiece W is attached misaligned with the table 24, a centrifugal force corresponding to the mass of the workpiece W and a torque corresponding to the gravity of the workpiece W act on the C-axis drive motor 46a. For this reason, the actual current value supplied from the C-axis drive unit 67 to the C-axis drive motor 46a is the reference current value to which current values corresponding to the centrifugal force and torque are added as fluctuation components.

[0074] Thus, according to this embodiment, the difference between the actual current value and the reference current value includes, as a fluctuation component, a current value corresponding to the torque according to the gravity of the workpiece W, which is not included in the conventional embodiment. Therefore, the degree of misalignment of the workpiece W with respect to the rotary table 24 can be detected more remarkably than in the conventional embodiment.

[0075] Thus, the misalignment detection device 75 and misalignment detection method according to this embodiment make it possible to detect with sufficient accuracy the degree of misalignment of the workpiece W relative to the turntable 24, even for a workpiece W that has been machined with a certain degree of precision and that itself has a certain degree of balance, compared to conventional methods. Furthermore, the degree of misalignment of the workpiece W relative to the turntable 24 can be detected more reliably regardless of the magnitude of the output of the C-axis drive motor 46a, which is the drive motor, and further regardless of the weight of the workpiece W. If the misalignment of the workpiece W relative to the turntable 24 exceeds a predetermined standard, measures can be taken, such as slowing down the acceleration / deceleration by reducing the time constant when rotating the turntable 24 or limiting the rotation speed of the turntable 24.

[0076] Although one embodiment of the present invention has been described above, the specific aspects that the present invention can adopt are not limited to the above-described embodiment.

[0077] For example, in the example described above, the misalignment detection unit 77 compares the difference between the actual current value corresponding to the rotational phase of the C-axis drive motor 46a and the reference current value with a predetermined threshold value, and if the difference value is greater than the threshold value, it is determined that some kind of action is required for misalignment, but this is not limited to this, and it is also possible to further calculate the difference between the maximum and minimum values of the difference value corresponding to the rotational phase of the C-axis drive motor 46a (see FIG. 17), and detect the degree of misalignment of the workpiece W from this maximum-minimum difference. In other words, the greater the maximum-minimum difference, the greater the amount of misalignment, and if this difference is greater than the predetermined threshold, it can be determined that some kind of action is required for misalignment.

[0078] Furthermore, in the above example, the table 24 is rotated so that its upper surface (mounting surface) is at an angle of 90° relative to the horizontal plane, but this is not limiting, and the table 24 may be tilted at a predetermined angle θ relative to the horizontal plane. Figure 18 shows the state in which the table 24 is tilted at angle θ. In this state, when the table 24 is rotated in the C-axis direction at a predetermined rotation speed, if the workpiece W is mounted misaligned with respect to the table 24 by a deviation amount r, the C-axis drive motor 46a is subjected to a centrifugal force (= mv 2 / r) and a torque (=r·mg·sinθ) corresponding to the gravity mg of the workpiece W acts, and the action of this torque (=r·mg·sinθ) makes it possible to detect the misalignment of the workpiece W with respect to the rotary table 24 more clearly than before.

[0079] The tilt angle θ of the rotary table 24 is preferably within the range of 15° to 90°, more preferably within the range of 30° to 90°, even more preferably within the range of 45° to 90°, and most preferably within the range of 60° to 90°. The greater the tilt angle θ of the rotary table 24, the more clearly the degree of misalignment of the workpiece W with respect to the rotary table 24 can be detected.

[0080] In addition, in the above example, the reference current value is obtained and then the actual current value is obtained, but this is not limited to this, and the order may be reversed, so that the actual current value is obtained and then the reference current value is obtained.

[0081] In the above example, the operation for acquiring the reference current value, the acquisition of the reference current, and the operation for acquiring the actual current value and the acquisition of the actual current are performed by manual operation via the input / output device 80. However, this is not limiting and these operations can be performed by a predetermined NC program. In this case, it is preferable that the NC program is stored in advance in the NC program storage unit 52 and executed by the program analysis unit 51. In this embodiment, a processing start signal for the misalignment detection unit 77 is transmitted from the program analysis unit 51 to the misalignment detection unit 77 (a transmission path from the program analysis unit 51 to the misalignment detection unit 77, shown by a dashed line in FIG. 2), and the misalignment detection process described above is performed by the misalignment detection unit 77. Alternatively, as shown by a dashed line in FIG. 2, the operation for acquiring the reference current value and the operation for acquiring the actual current value may be performed in response to an instruction (control signal) from the misalignment detection unit 77.

[0082] In the above example, the workpiece W is exemplified as the object to be placed and the object to be attached to the rotary table 24, and the workpiece W is attached directly to the table 24, but this is not limited to this. The workpiece W may be attached to a mounting jig attached to the table 24, in which case the mounting jig and the workpiece W correspond to the object to be placed, and the workpiece W corresponds to the object to be attached. Also, the mounting jig to which the workpiece W is attached may be attached to the table 24, in which case the mounting jig and the workpiece correspond to the object to be placed and also to the object to be attached.

[0083] To reiterate, the above-described embodiments are illustrative in all respects and are not limiting. Variations and modifications are possible for those skilled in the art. The scope of the present invention is defined not by the above-described embodiments but by the claims. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope of the claims and their equivalents. [Explanation of symbols]

[0084] 1 Machine tools 20 Swing table mechanism 24 Rotating Table 32a, 33a Y-axis drive motor 37a X-axis drive motor 40a, 41a Z-axis drive motor 50 Control device 51 Numerical Control Device 52 NC program memory section 53 Program Analysis Unit 55 Feed axis control section 65 Feed axis drive unit 75 Misalignment detection device 76 Reference current storage section 77 Misalignment detection unit

Claims

1. A method for detecting the degree of misalignment of the center of gravity of an object placed on the mounting surface of the rotary table with respect to the first axis in an apparatus having a flat mounting surface on which an object to be placed, including an attachment target, and a rotary table that rotates about a first axis perpendicular to the mounting surface and about a second axis parallel to the mounting surface, and a drive motor that rotates the rotary table, comprising: a reference current acquisition step of acquiring, as a reference current value, a drive current supplied to the drive motor when the rotary table is rotated around the first axis at a predetermined rotation speed in a reference state in which the mounting surface is horizontal and the mounting object is not attached; an actual current acquiring step of acquiring, as an actual current value, a drive current supplied to the drive motor when the turntable is rotated around the first axis at the rotation speed while the turntable is rotated around the second axis so that the mounting surface of the turntable forms a predetermined angle with respect to a horizontal plane after the object is mounted on the turntable; a misalignment detection step of calculating a difference between the actual current value and a reference current value, and detecting the degree of misalignment based on the calculated difference.

2. 2. The misalignment detection method according to claim 1, wherein the misalignment detection step detects the degree of misalignment based on the difference between the maximum and minimum values of the obtained difference values.

3. The misalignment detection method according to claim 1 or 2, characterized in that in the actual current acquisition process, the rotary table is rotated around the second axis so that its mounting surface is within a range of 15° to 90° with respect to a horizontal plane.

4. The present invention provides an apparatus having a flat mounting surface on which a mountable object including an attachment target is placed, a rotary table that rotates around a first axis perpendicular to the mounting surface and a second axis parallel to the mounting surface, and a drive motor that rotates the rotary table, the apparatus detecting the degree of misalignment of the center of gravity of the mountable object placed on the mounting surface of the rotary table with respect to the first axis, a reference current storage unit that stores, as a reference current value, a drive current supplied to the drive motor when the rotary table is rotated around the first axis at a predetermined rotation speed in a reference state in which the mounting surface is horizontal and the mounting object is not attached; and and a misalignment detection unit that acquires, in a state after an attitude change in which the rotary table, on which the object to be attached is attached, is rotated around the second axis so that the mounting surface of the rotary table forms a predetermined angle with respect to a horizontal plane, a drive current supplied to the drive motor when the rotary table is rotated around the first axis at the rotation speed, calculates a difference value between the acquired actual current value and the reference current value stored in the reference current memory unit, and detects the degree of misalignment based on the acquired difference value.

5. 5. The misalignment detection device according to claim 4, wherein the misalignment detection unit detects the degree of misalignment based on the difference between the maximum and minimum values of the obtained difference values.

6. The misalignment detection device according to claim 4 or 5, characterized in that the actual current value is the drive current when the rotary table is rotated around the second axis so that its mounting surface is within a range of 15° to 90° with respect to a horizontal plane.

7. A machine tool equipped with the misalignment detection device according to claim 4 or 5.

8. A machine tool equipped with the misalignment detection device according to claim 6.

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