JP2012198734A - Numerical controller and clamp release method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a numerical controller capable of promptly moving a control shaft in response to an instruction to move the control shaft, and a clamp release method.SOLUTION: A numerical controller outputs an unclamping signal to a clamp controller when receiving a control shaft movement instruction in executing an NC program (S11). The numerical controller transmits to a rotary table driving motor a first movement instruction for instructing movement of a rotary table by a minute movement amount out of a target movement amount (S16). The rotary table can move immediately after unclamping. A rotary table device can be driven at high speed. After the rotary table moves (S17: YES), the numerical controller transmits to the rotary table driving motor a second movement instruction for instructing movement by a remaining movement amount obtained by subtracting the minute movement amount from the target movement amount (S18). The rotary table can promptly move by the original target movement amount.

Description

  The present invention relates to a numerical control device and a clamp release method.

  There is a machine tool equipped with a rotary table device. The rotary table device holds the workpiece rotatably. The rotary table device includes a clamp mechanism. The clamp mechanism mechanically prevents the movement of the control shaft of the rotary table device so that the workpiece does not move when machining the workpiece. When a numerical control device that controls a machine tool moves a control shaft, the clamp by the clamp mechanism is first released (unclamped) to enable the movement of the control shaft. Next, the control axis is moved to the target position. Next, the machining operation is performed with the control shaft fixed by clamping by a clamping mechanism. The rotary table disclosed in Patent Document 1 gives a minute swing due to torque fluctuation that causes the servo motor to repeatedly rotate in the forward and reverse rotation directions and is in a clamped state based on the swing amplitude of the rotary table at that time. Confirm whether or not. This technique can also be applied to release the clamp. The servo motor is given a minute swing due to torque fluctuations that repeatedly rotate in the forward and reverse rotation directions, and it is confirmed whether or not it is in an unclamped state based on the swing amplitude of the rotary table.

Japanese Patent No. 4422187

  In the technique disclosed in Patent Document 1, after confirming that the control shaft is in an unclamped state, the movement is started from a state in which the control shaft is stopped. Therefore, there is a problem that it is not possible to promptly start from the confirmation of the unclamped state to the start of movement, and it takes time to move to the target position.

  An object of the present invention is to provide a numerical control device and a clamp release method capable of quickly moving a control shaft when an instruction to move the control shaft is given.

  A numerical control device according to a first aspect of the present invention includes a moving mechanism that moves a control shaft, a movement drive unit that drives the moving mechanism, and a clamp mechanism that blocks movement of the control shaft and releases the blocking. And a movement instruction determining means for determining whether or not there is an instruction to move the control axis, and the movement instruction determining means determines that the movement instruction has been issued. A release command output means for outputting a release command for instructing release of blocking of movement of the control shaft to the clamp mechanism, and when the release command output means outputs the release command, the control shaft is First movement command output means for outputting a first movement command for instructing movement of a predetermined movement amount among movement amounts to be moved to the movement drive unit; and movement determination means for determining whether or not the control shaft has moved. The transfer A second movement command for outputting a second movement command for instructing movement of a remaining movement amount obtained by subtracting the predetermined movement amount from the movement amount to the movement drive unit when the determination unit determines that the control shaft has moved; Output means.

  In the numerical control device according to the first aspect, when the release command output means outputs the release command, the first movement command output means outputs the first movement command to the movement drive unit. The first movement command is a command for instructing movement of a predetermined movement amount among movement amounts for moving the control axis. Therefore, the control shaft can move immediately after the inhibition of movement is released. When the movement determining unit determines that the control shaft has moved, the second movement command output unit outputs the second movement command to the movement driving unit. The second movement command is a command for instructing the movement of the remaining movement amount obtained by subtracting the predetermined movement amount from the movement amount. The control shaft can move the initial movement amount by moving the remaining movement amount. Therefore, this mode can move the control axis promptly when there is an instruction to move the control axis.

  Further, in the first aspect, the movement drive unit is a servo motor, and when the first movement command is output by the first movement output means, an output current output from the servo motor to the movement mechanism is generated. A current limiting means for limiting to a predetermined value or less may be provided. Even if the first movement command is output, the servo motor cannot move the control axis until the movement inhibition is released. The output current output from the servo motor to the moving mechanism increases. The current limiting means limits the output current output to the moving mechanism to a predetermined value or less. Therefore, this aspect can prevent the output current from rising excessively.

  Further, in the first aspect, an encoder for detecting the rotation of the shaft of the servo motor is provided, and the movement determining means determines that the control shaft has moved when the rotation of the shaft is detected by the encoder. Also good. Therefore, this aspect can reliably determine the movement of the control shaft.

  Moreover, the 1st aspect WHEREIN: When said 2nd movement command is output by said 2nd movement command output means, you may provide the cancellation | release means which cancels | releases the restriction | limiting of the said output current by the said current limiting means. Therefore, this aspect can return the output current of the servo motor to the normal state.

  The clamp release method according to the second aspect of the present invention includes a moving mechanism that moves the control shaft, a movement drive unit that drives the moving mechanism, and a clamp mechanism that prevents the movement of the control shaft and releases the blocking. A clamp release method performed by a numerical control device that controls a machine tool having a movement instruction determination step for determining whether or not there is an instruction to move the control axis, and the movement in the movement instruction determination step When the release command is output in the release command output step, the release command output step for outputting a release command to the clamp mechanism for instructing the release of the blocking of the movement of the control axis when it is determined that the release command is output. A first movement command output step for outputting a first movement command for instructing movement of a predetermined movement amount among movement amounts for moving the control axis to the movement drive unit; and A movement determination step for determining whether or not the movement has occurred; and a movement instruction step for instructing movement of a remaining movement amount obtained by subtracting the predetermined movement amount from the movement amount when it is determined that the control shaft has moved in the movement determination step. A second movement command output step of outputting a second movement command to the movement drive unit.

  In the clamp release method according to the second aspect, when the release command is output in the release command output step, the first movement command is output to the movement drive unit in the first movement command output step. The first movement command is a command for instructing movement of a predetermined movement amount among movement amounts for moving the control axis. Therefore, the control shaft moves immediately after the inhibition of movement is released. When it is determined that the control shaft has moved in the movement determination step, a second movement command is output to the movement drive unit in the second movement command output step. The second movement command is a command for instructing the movement of the remaining movement amount obtained by subtracting the predetermined movement amount from the movement amount. The control shaft can move the initial movement amount by moving the remaining movement amount. Therefore, this mode can move the control axis promptly when there is an instruction to move the control axis.

1 is a perspective view of a machine tool 1. FIG. 2 is a cross-sectional view taken along the line I-I in FIG. 1. 3 is a block diagram showing an electrical configuration of a numerical control device 50. FIG. It is a flowchart of a process control process. It is a flowchart of a control axis movement process. It is a timing chart of a control axis movement process.

  Hereinafter, a numerical controller 50 according to an embodiment of the present invention will be described with reference to the drawings. The numerical controller 50 controls the axis movement, cutting operation, tool change operation, and the like of the machine tool 1 shown in FIG. 1 based on the NC program. The machine tool 1 cuts the workpiece by relative movement between the workpiece (not shown) and the tool 6. The control axis refers to a mechanism for controlling movement on an additional axis different from the XYZ axes of the machine tool 1, and in this embodiment is a rotary table 4 (see FIG. 2).

  The structure of the machine tool 1 will be briefly described. As shown in FIG. 1, the machine tool 1 includes a base 2, a column 5, a spindle head 7, a spindle (not shown), a rotary table device 10, and the like. The column 5 is erected on the upper rear side of the base 2. The spindle head 7 moves up and down along the front surface of the column 5. The spindle head 7 moves in the Z-axis direction by driving the Z-axis motor 73. The main shaft is provided below the main shaft head 7. The spindle has a mounting portion (not shown) for mounting the holder 16 of the tool 6, and rotates by driving the spindle motor 74. The tool 6 is, for example, a drill, a center drill, a tap or the like. The tool 6 rotates together with the spindle and cuts the workpiece held by the rotary table device 10. A tool changer (not shown) replaces the tool 6 mounted on the main shaft with another tool as appropriate.

  The rotary table device 10 is fixed on a slide table 15 provided on the upper part of the base 2. The slide table 15 is movable in the XY axis direction within a horizontal plane. The rotary table device 10 rotates the workpiece on the rotary table 4 (see FIG. 2). The machine tool 1 feeds a workpiece in the X and Y directions by the slide table 15, rotates the rotary table 4 of the rotary table device 10, and fixes (clamps) it at a set position for cutting.

  The structure of the rotary table device 10 will be described. As shown in FIG. 2, the rotary table device 10 includes a cylindrical housing 21. The housing 21 has a bearing 22 attached to the inside by screws 46. The housing 21 integrally supports a large gear 26 and a spindle 23 so as to be rotatable coaxially. The large gear 26 and the spindle 23 are fixed by screws 45 with the bearing 22 interposed therebetween. The housing 21 supports the pinion 25 in a rotatable manner. The pinion 25 meshes with the large gear 26 in a positional relationship orthogonal to the rotation axis of the large gear 26. The pinion 25 and the large gear 26 constitute a staggered bevel gear mechanism.

  A disk-shaped rotary table 4 is attached to one end of the spindle 23 in the axial direction with screws 47. The rotary table 4 holds a workpiece with a holder (not shown). A boss 28 is attached with a screw 48 to the other end of the spindle 23 opposite to the one end. A disk 32 is sandwiched between the spindle 23 and the boss 28. An O-ring 42 is sandwiched between the disk 32 and the spindle 23. An O-ring 41 is sandwiched between the disk 32 and the boss 28.

  On the surface of the housing 21 opposite to the rotary table 4, a ring-shaped cylinder 29 is fixed with a packing 37 sandwiched by screws 49. The cylinder 29 has an oil seal 44 attached to the inner periphery. The cylinder 29 houses a ring-shaped piston 30 therein. The piston 30 is provided with an O-ring 38 on the outer peripheral portion and an O-ring 39 on the inner peripheral portion. The piston 30 is slidable in the axial direction of the housing 21. The cylinder 29 is provided with a vent hole 35. A surface of the housing 21 facing the cylinder 29 is provided with a recess 33. The recess 33 has a spring 34 disposed inside. The spring 34 presses the piston 30 against the cylinder 29 side. The packing 37 and the O-rings 41 and 42 prevent cutting oil or the like from entering the clamp mechanism and reducing the frictional force.

  The clamping operation and unclamping operation in the rotary table device 10 will be described. In the unclamped rotary table 4, when the numerical controller 50 first drives the rotary table drive motor 75, the pinion 25 rotates. The large gear 26 that meshes with the pinion 25 rotates about an axis perpendicular to the axis of the pinion 25 by the support of the bearing 22. When the large gear 26 rotates, the spindle 23, the rotary table 4, the boss 28, and the disk 32 rotate. Therefore, the workpiece held by the rotary table 4 rotates on the control axis of the rotary table 4.

  When the rotary table drive motor 75 stops driving, the pinion 25 and the large gear 26 stop rotating. The spindle 23, the rotary table 4, the boss 28, and the disk 32 also stop rotating. The rotation of the turntable 4 stops. The numerical controller 50 injects air from the vent hole 35. The piston 30 moves in the direction of the housing 21 by the pressure of the injected air. The pressure of the injected air exceeds the spring force of the spring 34. The piston 30 contacts the disk 32. The disk 32 is elastically deformed. The piston 30 presses and holds the elastically deforming disk 32 against the housing 21. A frictional force is generated between the disk 32 and the housing 21. The frictional force restrains the movement of the disk 32 and the spindle 23. The rotary table 4 is in a clamped state. The machine tool 1 can cut a workpiece.

  The numerical control device 50 releases (unclamps) the rotary table 4 again in order to change the angle of the workpiece with the tool 6. The numerical controller 50 first outputs an unclamp signal to the clamp controller 80. The clamp control device 80 releases the air pressure applied to the vent hole 35. The piston 30 moves in the direction of the cylinder 29 by the spring force of the spring 34. The disk 32 is elastically restored by the elastic force of the spring 34. Since the disk 32 is separated from the housing 21, the frictional force is eliminated. The rotary table 4 is in an unclamped state, and the spindle 23 can rotate. The rotary table 4 rotates by the target movement amount set by the NC program and stops. The numerical controller 50 puts the rotary table 4 in the clamped state again. The machine tool 1 performs cutting on a workpiece from another angle.

  As will be described later, the numerical controller 50 according to the present embodiment outputs a first movement command for instructing movement of a minute movement amount in the same direction as the target movement amount to the rotary table drive motor 75 simultaneously with the output of the unclamp signal. . Therefore, the rotary table 4 can start rotating immediately after switching to the unclamped state.

  The electrical configuration of the numerical controller 50 will be described. As shown in FIG. 3, the numerical controller 50 includes a CPU 51, a ROM 52, a RAM 53, a flash memory 54, an input interface 55, an output interface 56, drive circuits 61 to 65, a control circuit 66, and the like. The CPU 51, ROM 52, RAM 53, flash memory 54, input interface 55, and output interface 56 are connected by a bus 58. The ROM 52 stores the control axis movement program of the present invention in addition to the machining control program for controlling the machining operation of the numerical controller 50. The RAM 53 temporarily stores various data for executing various processes described later. The flash memory 54 stores an NC program (machining program) composed of NC commands. The input interface 55 is connected to the operation device 17 and an encoder 76 provided on the rotary table drive motor 75. The operating device 17 is a device that includes a plurality of command keys that command starting and stopping of the machine tool 1, input keys, editing keys, and the like.

  The drive circuit 61 drives the X axis motor 71. The drive circuit 62 drives the Y axis motor 72. The drive circuit 63 drives the Z-axis motor 73. The drive circuit 64 drives the spindle motor 74. The drive circuit 65 drives the rotary table drive motor 75. The control circuit 66 controls the clamp control device 80. The clamp control device 80 controls the clamping operation and the unclamping operation of the rotary table device 10. The drive circuits 61 to 65 and the control circuit 66 are connected to the output interface 56.

  The minute movement amount of the rotary table 4 preset by the operator will be described. In this embodiment, simultaneously with the output of the unclamp signal, the minute movement amount for rotating the turntable 4 is output to the turntable drive motor 75 as a first move command. The minute movement amount is set to a value smaller than the target movement amount set by the control axis movement command of the NC program. For example, when the target movement amount is 100 °, the minute movement amount is set to 0.05 to 0.1 °. The rotation direction of the minute movement amount is the same direction as the rotation direction of the target movement amount. The operator inputs a minute movement amount in advance using the operation device 17. The CPU 51 stores the minute movement amount input by the worker in the flash memory 54 (see FIG. 3).

  The machining control process by the CPU 51 will be described with reference to the flowchart of FIG. The operator presses a machining start switch (not shown) of the operation device 17. The CPU 51 reads the machining control program stored in the ROM 52 and executes this processing. The CPU 51 reads the NC program stored in the flash memory 54 and interprets it as one block (S1). The CPU 51 determines whether or not the interpreted NC command is M30 (end command) (S2). When the CPU 51 determines that the interpreted NC command is M30 (S2: YES), the CPU 51 ends the process. When the CPU 51 determines that the interpreted NC command is not M30 (S2: NO), it determines whether the interpreted NC command is a control axis movement command (S3). The control axis movement command is a command for instructing the rotation and movement amount (rotation amount) of the rotary table 4. When the CPU 51 determines that the interpreted NC command is a control axis movement command (S3: YES), the CPU 51 executes a control axis movement process described later (S5). When the CPU 51 determines that the interpreted NC command is a command other than the control axis movement command (S3: NO), the CPU 51 executes processing according to the control command (S4). The CPU 51 moves to the next block (S6), and returns to S1 to repeat the process until the end command is read.

  The control axis movement process by the CPU 51 will be described with reference to the flowchart of FIG. 5 and the timing chart of FIG. The control axis movement process is a process of changing the angle of the workpiece with respect to the tool 6 by unclamping the rotary table 4 and rotating the target movement amount. When the NC command interpreted in S1 (see FIG. 4) of the machining control process is a control axis movement command (S3: YES), the CPU 51 reads and executes the control axis movement program stored in the ROM 52. To do.

  The CPU 51 outputs an unclamp signal to the clamp control device 80 at the timing t1 in FIG. 6 (S11). Further, the CPU 51 determines whether or not the target movement amount set by the control axis movement command is larger than the minute movement amount stored in the flash memory 54 (S12). When the CPU 51 determines that the target movement amount is larger than the minute movement amount (S12: YES), the CPU 51 determines the minute movement amount as the first movement command (S13). When the CPU 51 determines that the target movement amount is equal to or less than the minute movement amount (S12: NO), the CPU 51 determines the target movement amount as it is as the first movement command (S14).

  The CPU 51 transmits a current limit signal to the rotary table drive motor 75 at timing t2 (S15). The rotary table drive motor 75 is a servo motor. Servo motors generally have the property that when the output shaft does not rotate, the load torque increases and the output current increases accordingly. The current limit signal is a signal for limiting the output current of the servo motor to a predetermined value or less so as not to increase excessively. Note that the timing for transmitting the current limit signal may be the timing t1 when the unclamp signal is output.

  The CPU 51 transmits the first movement command determined in S13 or S14 to the rotary table drive motor 75 (S16). The CPU 51 executes the processes from S11 to S16 at the same timing. The clamp control device 80 that has received the unclamp signal starts the unclamping operation of the clamp mechanism. The CPU 51 transmits the first movement command to the rotary table drive motor 75, but the rotary table 4 does not rotate until the unclamping operation of the clamp mechanism is completed. Although the output current of the rotary table drive motor 75 increases, the output current changes to a predetermined value or less because the current limit is executed. The first movement command is a command for slightly moving in the same direction as the target movement amount. Therefore, the load applied to the rotary table drive motor 75 and the clamp mechanism of the rotary table device 10 can be minimized.

  The CPU 51 determines whether or not the turntable 4 has moved (rotated) (S17). The CPU 51 can detect the movement of the rotary table 4 by detecting the rotation of the output shaft of the rotary table drive motor 75 with the encoder 76. Until the CPU 51 determines that the rotary table 4 has moved (S17: NO), the CPU 51 returns to S17 and enters a standby state.

  The clamp control device 80 that has received the unclamp signal releases the air pressure applied to the vent hole 35. The piston 30 moves in the direction of the cylinder 29 by the spring force of the spring 34. The disk 32 is elastically restored by the elastic force of the spring 34. Since the disk 32 is separated from the housing 21, the frictional force is eliminated. The rotary table 4 enters an unclamped state at the timing t4 in FIG. The load in the same direction as the target movement amount is applied to the output shaft of the rotary table drive motor 75 from the time when the clamp control device 80 starts the unclamping operation. Therefore, the turntable 4 starts to rotate from the timing t3 when the turntable 4 switches to the unclamped state.

  When the CPU 51 determines that the rotary table 4 has moved (S17: YES), the CPU 51 calculates the remaining movement amount obtained by subtracting the movement amount specified by the first movement command from the target movement amount, and drives the rotary table as the second movement command. The data is transmitted to the motor 75 (S18). The rotary table 4 starts to rotate immediately after switching to the unclamped state. The rotary table 4 can continue to move the remaining moving amount as it is after the timing t4 when the moving amount is moved. The CPU 51 transmits a current limit release signal to the turntable drive motor 75 (S19). Therefore, the output current of the rotary table drive motor 75 returns to normal. The rotary table 4 reaches the maximum speed at timing t5, gradually decelerates at timing t6, and stops at timing t7 when the target movement amount is reached. Therefore, the turntable 4 can smoothly move the target movement amount immediately after switching to the unclamped state. The rotary table device 10 can be driven at high speed.

  The CPU 51 performs an in-position check and determines whether or not the turntable 4 has completed the movement of the target movement amount (S20). Until the movement of the target movement amount of the rotary table 4 is completed (S20: NO), the CPU 51 returns to S20 and enters a standby state. When the CPU 51 determines that the movement of the target movement amount is completed (S20: YES), the CPU 51 stops outputting the unclamp signal at the timing t8 (S21). Since the output of the unclamp signal is stopped by the CPU 51, the clamp control device 80 injects air into the vent hole 35 and returns the clamp mechanism of the rotary table device 10 to the clamped state. The CPU 51 ends the control axis movement process, and proceeds to S6 of the main machining control process shown in FIG.

  In the above description, the rotary table 4 shown in FIG. 2 corresponds to the control shaft of the present invention, the rotary table device 10 corresponds to the moving mechanism of the present invention, and the rotary table drive motor 75 corresponds to the moving drive unit of the present invention. The disk 32, the cylinder 29, the piston 30, the spring 34, and the clamp control device 80 correspond to the clamp mechanism of the present invention. The CPU 51 that executes S3 of FIG. 4 corresponds to the movement instruction determination means of the present invention, the CPU 51 that executes the process of S11 of FIG. 5 corresponds to the release command output means of the present invention, and the CPU 51 that executes the process of S16 is The CPU 51 that executes the process of S17 corresponds to the movement determination means of the present invention, and the CPU 51 that executes the process of S18 corresponds to the second movement command output means of the present invention. To do. The CPU 51 that executes the process of S15 corresponds to the current limiting means of the present invention, and the CPU 51 that executes the process of S19 corresponds to the releasing means of the present invention.

  As described above, the numerical controller 50 according to the present embodiment outputs an unclamp signal to the clamp controller 80 when there is a control axis movement command for the rotary table 4 of the rotary table device 10 in the NC program. Then, the first movement command for instructing the movement of the minute movement amount of the target movement amount for moving the rotation table 4 is transmitted to the rotation table drive motor 75. Therefore, the rotary table 4 can be moved immediately after being unclamped. The rotary table device 10 can be driven at high speed. When the turntable 4 further moves, a second movement command that instructs the movement of the remaining movement amount obtained by subtracting the minute movement amount from the target movement amount is transmitted to the rotation table drive motor 75. Therefore, the rotary table 4 can quickly move the initial target movement amount.

  In this embodiment, in particular, the rotary table drive motor 75 is a servo motor. When the first movement command is transmitted to the rotary table drive motor 75, a current limit signal is transmitted to the rotary table drive motor 75. Therefore, it is possible to prevent the output current of the rotary table drive motor 75 from excessively rising until the unclamping of the rotary table 4 is completed.

  In this embodiment, in particular, the encoder 76 detects the rotation of the output shaft of the rotary table drive motor 75. Therefore, it can be determined accurately and promptly that the rotary table 4 has moved.

  In the present embodiment, in particular, when the second movement command is transmitted to the turntable drive motor 75, a current limit release signal is output to the turntable drive motor 75. Therefore, the output current of the rotary table drive motor 75 can be returned to the normal state.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the rotary table device 10 that rotates the rotary table 4 is described as an example of the moving mechanism that moves the control shaft. However, the present invention can be applied to, for example, a table device that linearly moves the table.

  Further, whether or not the rotary table 4 has moved in S17 of FIG. 5 is determined by whether or not the rotary table 4 has moved a minute movement amount. If the feedback signal from 76 is input several pulses, it may be determined that the movement has occurred. In this case, the current limit release signal is transmitted after the rotary table 4 has moved a small amount of movement.

  Moreover, although the numerical control apparatus 50 provided with the electric current limiting means and the cancellation | release means was demonstrated in the said embodiment, these may not necessarily be provided.

DESCRIPTION OF SYMBOLS 1 Machine tool 4 Rotary table 10 Rotary table apparatus 29 Cylinder 30 Piston 32 Disc 34 Spring 50 Numerical control apparatus 51 CPU
52 ROM
75 Rotary table drive motor 76 Encoder 80 Clamp control device

Claims (5)

A numerical control device that controls a machine tool having a moving mechanism that moves a control shaft, a moving drive unit that drives the moving mechanism, and a clamp mechanism that blocks movement of the control shaft and releases the blocking. And
Movement instruction determination means for determining whether or not there is an instruction to move the control axis;
A release command output means for outputting, to the clamp mechanism, a release command for instructing cancellation of the movement of the control shaft when the movement instruction determination means determines that the movement instruction has been issued;
When the release command output means outputs the release command, a first movement command output that outputs a first movement command for instructing a movement of a predetermined movement amount among the movement amounts for moving the control shaft to the movement drive unit. Means,
Movement determining means for determining whether or not the control axis has moved;
When the movement determining means determines that the control shaft has moved, a second movement command for instructing movement of a remaining movement amount obtained by subtracting the predetermined movement amount from the movement amount is output to the movement drive unit. A numerical control device comprising a movement command output means. The movement drive unit is a servo motor,
And a current limiting unit configured to limit an output current output from the servo motor to the moving mechanism to a predetermined value or less when the first movement command is output by the first movement output unit. Item 2. The numerical control device according to Item 1. An encoder for detecting rotation of the shaft of the servo motor;
The numerical control apparatus according to claim 2, wherein the movement determination unit determines that the control shaft has moved when rotation of the shaft is detected by the encoder.   4. The apparatus according to claim 2, further comprising a release unit that releases the restriction of the output current by the current limiting unit when the second movement command is output by the second movement command output unit. Numerical control unit. The numerical control device controls a machine tool having a moving mechanism for moving the control shaft, a moving drive unit for driving the moving mechanism, and a clamp mechanism for preventing and releasing the movement of the control shaft. A method of releasing the clamp,
A movement instruction determination step for determining whether or not there is an instruction to move the control axis;
A release command output step of outputting a release command for instructing release of blocking of the movement of the control shaft to the clamp mechanism when it is determined in the movement command determination step that the movement is instructed;
When the release command is output in the release command output step, a first movement command output that outputs a first movement command for instructing a movement of a predetermined movement amount among the movement amounts for moving the control shaft to the movement drive unit Process,
A movement determining step of determining whether or not the control axis has moved;
When it is determined in the movement determination step that the control shaft has moved, a second movement command for instructing movement of a remaining movement amount obtained by subtracting the predetermined movement amount from the movement amount is output to the movement drive unit. A clamp release method comprising: a movement command output step.

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