JPH088046Y2 - NC control tool change arm unit - Google Patents

Description

[Detailed Description of the Invention] Industrial field of use [Technical Field] The present invention relates to an NC-controlled tool changing arm unit of an automatic tool changing device for an NC machine tool such as a machining center.

2. Description of the Related Art Conventionally, there are two types of turning and removing operations of a tool changing arm of an automatic tool changing device such as a machining center, which uses a fluid pressure as a driving source and a cam type which uses an AC motor as a driving source as viewed from the driving system. is there. The cam type has a complicated structure,
It is difficult to save space because a large amount of damage is caused in a collision accident due to erroneous operation, a safety device is required, and so on. For this reason, for example, in a relatively large portal machining center where a 90 ° angular attachment can be mounted on the machine spindle, there is a distance between the tool magazine device and the spindle head, and a carrier for transportation is required to shorten the replacement time. In addition, the tool change arm unit provided on the carrier must be able to swivel 90 ° to accommodate both horizontal and horizontal spindles, and a fluid pressure drive type with a simple structure is used. Is normal. As shown in FIG. 6, this fluid pressure driven tool changing arm unit has a swivel shaft provided so as to swivel and unscrew in a box that can swivel 90 ° about a swivel center a in the X-axis vertical plane. Tool exchange arm 102 is fixed to the tip of 101, hydraulic linear cylinder 103 performs insertion / extraction operation, and hydraulic swivel cylinder 104 drives gears 105, 1
The turning motion is performed via 06.

Problems to be Solved by the Invention The fluid pressure drive type tool changing arm unit described in the conventional technique has a problem that it takes a long time to perform the changing operation while confirming each operation. are doing.

The present invention has been made in view of the above problems of the conventional technology, and an object of the present invention is to provide a simple and small-sized tool with a short replacement time in which replacement operation control is performed by an NC-controlled servomotor. It is intended to provide a replacement arm unit.

Means for Solving the Problems In order to achieve the above object, the NC control tool change arm unit in the present invention is designed to automatically move a tool between a tool magazine device and a spindle of an NC machine tool by rotating and removing the tool change arm. In an automatic tool changer for exchanging, one servomotor whose rotation is controlled by an NC device is provided, and switching means is provided for switching and transmitting the driving force of the servomotor between turning and unplugging of the tool changing arm. Brake means for operating other than power transmission is provided on each of the swivel drive system path and the insertion / removal drive system path of the tool changing arm, and the NC device is provided with a motor when the tool changing arm is overloaded more than a set value. It is provided with a safety function of detecting a torque increase by means of detecting a current value equal to or more than a set value and making the motor torque zero. In addition, in the automatic tool changer that automatically changes the tool by moving the carrier between the tool magazine device of the NC machine tool and the spindle, turning the tool changing arm, and inserting / removing the tool, one servo controlled by the NC device is rotated. A first gear and a second gear that are provided with a motor and transmit rotation on the output axis of the servo motor
A gear is provided, a clutch for switching a transmission system path between the first gear and the second gear is provided, a first intermediate gear member meshing with the first gear is attached, and a ball screw rotatably supported is provided. The first intermediate gear member is provided with a brake means for applying a brake except when power is transmitted, and a ball nut that is screwed into the ball screw and is movable in the axial direction of the screw is provided.
A twin-type tool exchange arm member that is connected to the ball nut and is movable in a direction parallel to the ball screw is provided, and a second intermediate gear member to which the rotation is transmitted from the second gear is attached, and the drive is rotatably supported. The shaft is provided with a braking means for applying a brake in addition to the power transmission, and a spline shaft supported by the tool exchange arm member by spline fitting and rotatably supported is provided, and the spline shaft and the drive shaft of the second intermediate gear member are provided. A speed reducer for decelerating rotation is installed between the NC device and the NC device detects torque up by means of detecting a current value above the set value of the motor when an overload above the set value acts on the tool change arm. Then, it is provided with a safety function of reducing the torque of the motor to zero.

In addition, in an automatic tool changer that automatically changes tools by moving the carrier between the tool magazine device of the NC machine tool and the spindle and turning and removing / inserting the tool change arm, the NC device for turning the tool change arm rotates the tool. A first servo motor to be controlled is provided, a pulley connected to the output shaft of the first servo motor and a pulley by a timing belt is attached, a drive shaft rotatably supported is provided, and the drive shaft rotates on the same axis as the drive shaft. A spline shaft provided so that it is possible only, and a speed reducer for decelerating and transmitting the rotation is provided between the spline shaft and the drive shaft.
A second servo motor, whose rotation is controlled by the NC device, is installed.
A ball screw supported by a pulley connected to the output shaft pulley of the second servo motor with a timing belt is rotatably supported, and a ball nut screwed to the ball screw and movable in the screw axis direction is provided. A twin type tool changing member connected to the ball nut and fitted to the spline shaft and movable in the axial direction is provided, and the NC device is provided with a motor of the motor when an overload of a set value or more acts on the tool changing arm. It is provided with a safety function of detecting a torque increase by means of detecting a current value equal to or more than a set value and making the motor torque zero.

The NC control tool exchange arm unit according to claims 1 and 2 switches and transmits the rotational force of one drive motor that is rotationally controlled by the NC by the electromagnetic clutch to alternately insert and remove the ball screw and the arm turning axis. Drive to perform the tool change arm replacement operation. When a collision occurs during the exchange operation, damage is avoided by the safety function of the torque guard.

In the NC control tool exchange arm unit according to claims 3 and 4, the ball screw and the arm pivot shaft are respectively driven by two drive motors for insertion / removal and rotation which are rotationally controlled by the NC to exchange the tool exchange arm. Take action. When a collision occurs during the exchange operation, damage is avoided by the safety function of the torque guard.

First Embodiment A first embodiment will be described with reference to FIGS. 1 to 4.

In a well-known portal machining center, a table 2 is movably positioned on a guide surface in the X-axis direction provided on a bed 1, and a top beam is placed on a column 3 erected on both floors of the bed 1. 4 is attached.
A sliding surface in the Z-axis direction is cut on the front surface of the column 3, and a cross beam 5 is provided on the sliding surface so as to be movable and positionable. A sliding surface in the Y-axis direction is cut on the cross beam 5, and a spindle head 6 is mounted on the sliding surface so as to be movable and positioned. A spindle sleeve 10 is provided on the spindle head 6 so as to be movable and positioned in the Z-axis direction, and a spindle 7 is rotatably supported by the spindle sleeve 10 by a plurality of bearings. A spindle tool pulling device (not shown) is incorporated in the spindle head.

A tool magazine device 8 is provided on the left side surface of the column 3. A plurality of magazine pots for storing a plurality of tools in the Y-axis direction leftward are endlessly connected to the tool magazine device 8 by a link-like chain, and a specified index pot is moved to the front tool exchange position by a turning indexing device (not shown). It is designed to turn and index. In the magazine frame of the tool magazine device 8, a not-shown ready station pot is provided in the vicinity of the tool exchange position so as to be rotatable by 90 °, and a sub-arm device for exchanging tools between the magazine pot and the ready station pot is provided near this. Has been.

On the sliding surface of the cross beam 5 in the Y-axis direction, a carrier 9 for carrying a tool between the spindle head 6 and the tool magazine device 8 is provided so as to be movable and positioned, and the carrier 9 has a tool exchange arm unit. 11 is provided so as to be capable of 90 ° swivel indexing about a swivel center axis 12 in the Y-axis direction. A hollow arm swivel shaft 14 is rotatably supported by bearings 15 and 16 in the frame 13 of the tool exchanging arm unit 11, and a longitudinal half thereof projects from the end face of the frame. A female spline 17 is fitted on the tip portion. The hollow shaft 18 is fitted to the outer periphery of the protruding portion of the arm swivel shaft 14 so as to be movable in the axial direction, the tip of the spline shaft 21 is fixed to the lid 19 fixed to the tip of the hollow shaft 18, and the spline shaft 21 is It is engaged with the female spline 17. A twin type tool exchange arm 22 having tool gripping grippers on both sides is fixed to the hollow shaft 18 at a position near the frame 13. An NC-driven servomotor 23 is fixed to the frame body 13 in parallel with the arm turning shaft 14, and a gear 24 is fitted to an output shaft 23a of the servomotor 23. Holes 13a and 13b are formed in the frame body 13 concentrically with the servo motor 23, and an arm turning gear 26 is rotatably supported in the hole 13a by a plurality of bearings 25. A sleeve 28 is rotatably supported by a plurality of bearings 27 in the center hole of the gear 26, an internal gear 30 engraved in the center hole of the sleeve 28 is engaged with the gear 24, and a gear clutch is formed. .
Further, a drive shaft 29 is rotatably supported by a plurality of bearings at the tip of the central hole of the sleeve 28, and a gear 31 for arm insertion / removal is fitted to the tip of the drive shaft 29.
It is rotatably supported by a bearing on 13b. Drive shaft 29
An electromagnetic tooth clutch 32 is provided at the center of the electromagnetic tooth clutch 32.When the electromagnetic tooth clutch 32 is not energized, the clutch surface is always engaged with the arm turning gear 26 side by a spring (not shown). Engage with. The clutch surface is always engaged with one of the gears 26 or 31 and has no neutral position, and switching is always performed when the servomotor 23 is stopped. Further, the clutch surface adopts a fixed point meshing method on the circumference, and it is always engaged at the same position so that the phase of the inserting / removing operation of the tool changing arm and the pivoting operation are surely maintained.

A rolling ball screw 33 is rotatably supported by a plurality of bearings parallel to the center of the servo motor 23 and the arm turning shaft 14, and a joint shaft 34 is fitted to the rear end of the rolling ball screw 33.
The joint shaft 34 is rotatably supported by the frame 13 by a plurality of bearings. Then, a gear 35 is fitted to the rear end of the joint shaft 34, and the gear 35 is rotatably supported by the frame through a bearing,
It is meshed with the gear 31. Further, an electromagnetic brake 36 is provided at the center of the joint shaft 34, and the electromagnetic brake 36 is energized and non-electrostatically charged together with the electromagnetic tooth clutch, and is released when energized and braked by spring force when non-electrostatically applied. There is.

A guide shaft 37 for insertion / removal is provided so as to be movable in the axial direction in parallel with the rolling ball screw 33 and the vicinity of the arm turning shaft 14.
The guide shaft 37 is fixed at its rear end to a ball nut 38 screwed to the rolled ball screw 33 via a connecting metal fitting 39, and at its front end is attached / detached with a bracket 41. It is engaged with the outer circumference. Further, an intermediate gear 42 is rotatably supported by a center portion of the joint shaft 34 via a bearing, and the gear 42 is meshed with the gear 26. A swivel drive shaft 43 is rotatably supported by a plurality of bearings in a concentric hole of the arm swivel shaft 14 of the frame body 13, and a gear 45 is fitted to the swivel drive shaft 43 via a phase adjusting Schupan ring 44. The gear 45 is meshed with the intermediate gear 42. Further, an electromagnetic brake 46 is provided at the center of the turning drive shaft 43,
The electromagnetic brake 46 is energized when the electromagnetic tooth clutch 32 is not energized to release the brake.
The swing drive shaft 43 is connected to the speed reducer 47, and the speed reducer 47 is a joint.
It is connected to the swivel shaft 14 via 48.

A 90 ° angular attachment 51 can be removably attached to the spindle sleeve 10 as required. As shown in FIG. 4, the 90 ° angular attachment 51 has an attachment main body 53 in which an attachment main spindle 53 whose axis is orthogonal to the main spindle 7 is rotatably supported.
Driven by Furthermore, the attachment is equipped with a tool pulling mechanism and indexing mechanism.
With this indexing mechanism, it is possible to turn and index in a horizontal plane.

If the tool change arm 22 is overloaded in the NC device during operation due to a collision or the like, the torque of the drive motor is detected by the means for detecting the current value above the set value and the servo motor 23 It has a safety function of a torque card that makes the motor torque zero, that is, free, and avoids damage due to a collision or the like.

 Next, the operation of the first embodiment will be described.

Now, the cutting work is performed by the tool attached to the spindle 7, and the next tool selected from the tool magazine device 8 by the next tool command of NC is gripped by one gripper of the tool exchanging arm 22 to move downward. The carrier 9 stands by at a predetermined position on the tool magazine device 8 side.

After cutting with the spindle mounting tool, the spindle sleeve
10 moves upward in the Z-axis direction and is positioned at a predetermined tool exchange position, a tool exchange command is issued from the NC, the carrier 9 moves to the Y-axis direction main spindle side, and is moved to the tool exchange position on the left side of the main spindle head 6. Once positioned, the other empty gripper of the tool change arm 22 grips the spindle tool. Then, the tool pulling device is operated to release the clamp of the spindle tool, the electromagnetic tooth clutch 32 is energized, the clutch surface is engaged with the inserting / removing gear 31 side, and at the same time, the electromagnetic brake 36 is energized, so that the joint shaft 34 The brake is released. Next, the servo motor 23 is rotated by NC control, the rolling ball screw 33 is rotated via the gears 31, 35, and the joint shaft 34, and the ball nut 38 is moved downward in the Z-axis direction, and the coupling fitting 39 and the guide are guided. The tool exchanging arm 22 descends via the shaft 37, the bracket 41, and the hollow shaft 18, and the used tool is extracted from the main shaft 7. The extraction speed of the tool change arm 22 at this time is controlled by the speed command set in the speed parameter in the NC, and the extraction is performed at a relatively high speed at an appropriate start / stop speed that suppresses shock. Servomotor
When the rotation of 23 is stopped, the electromagnetic brake 36 is de-energized and the rolled ball screw 33 is braked. At the same time, the electromagnetic tooth clutch 32 is de-energized and the clutch surface is the gear.
26 is engaged, the electromagnetic brake 46 is energized, and the brake of the turning drive shaft 43 is released. Then again servo motor
23 is rotated, the swing drive shaft 43 is rotated through the gear 26, the intermediate gear 42, and the gear 45, the spline shaft 21 is rotated through the speed reducer 47, the joint 48, and the female spline 17, the lid 19, and the hollow. axis
The tool change arm 22 is swung 180 ° via 18 by the same speed control method as described above. With this turning, the positions of the tools gripped by both grippers are exchanged, and when the rotation of the servo motor 23 is stopped, the electromagnetic brake 46 is de-energized,
The swing drive shaft 43 is braked and the electromagnetic tooth scratch
32 is energized to engage the clutch surface on the gear 31 side, and the electromagnetic brake 36 is energized to release the brake of the rolled ball screw 33. Next, the servo motor 23 is rotated in the reverse direction, the tool exchanging arm 22 is raised, and the next tool is inserted into the spindle 7.
It is clamped to the spindle 7 by a tool pulling device. Then, when the carrier 9 starts moving to the tool magazine device 8 side, the tool changing arm 22 is separated from the next tool, and the carrier 9 is positioned at a predetermined position near the ready station pot. Next, the used tool is once inserted into the ready station pot by the turning and removing operations of the tool changing arm 22, and then returned to the magazine pot by the sub-arm device.

Next, a tool exchange operation when the 90 ° angular attachment 51 is attached to the spindle sleeve 10 will be described.

When the cutting process by the tool mounted on the attachment spindle 53 is completed, the spindle sleeve 10 is moved upward in the Z-axis direction to be positioned at a predetermined tool replacement position, the attachment body 52 is swung, and the attachment spindle 53 is moved to the X-axis. Direction is indexed forward. In response to the NC tool change command, the one tool gripper of the tool change arm 22 holds the next tool, and the tool change arm unit 11 on standby with the next tool facing down
The arm revolving shaft 14 is turned 90 degrees in the X-axis direction, and the tool changing arm 22 faces the front side. Then, the carrier 9 is moved to the spindle head 6 side in the Y-axis direction to be positioned at the tool changing position on the left side of the spindle head 6, and the other empty gripper of the tool changing arm 22 grips the used tool of the attachment spindle. Next, the tool pulling mechanism is operated to release the clamp of the used tool, the electromagnetic tooth clutch 32 and the electromagnetic brake 36 are energized, and the clutch surface is engaged with the extraction / insertion gear 31 side,
The brake of the rolled ball screw 33 is released. Next, the servo motor 23 is rotated, the tool exchanging arm 22 moves forward in the X-axis direction, the used tool is extracted from the attachment spindle 53, and the rotation of the servo motor 23 is stopped. Next, the electromagnetic brake 36 is de-energized, the rolling ball screw 33 is braked, the electromagnetic tooth clutch 32 is de-energized at the same time, the clutch surface is engaged with the turning gear 26 side, and the electromagnetic brake 46 is energized. The brake of the swing drive shaft 43 is released. Next, the servo motor 23 is rotated again, and the tool exchanging arm 22 pivots 180 ° and the positions of both gripped tools are exchanged. Next, after the electromagnetic tooth clutch 32 and the electromagnetic brake 36 are simultaneously energized, the servo motor 23 is rotated in the reverse direction, the tool changing arm 22 is moved rearward in the X-axis direction, and the next tool is inserted into the attachment spindle 53, It is clamped by the pulling mechanism. Then, when the carrier 9 starts moving to the tool magazine device 8 side, the tool changing arm 22 is separated from the next tool, and the carrier 9 is positioned at a predetermined position near the ready station pot. Next, the tool changing arm unit 11 is turned by 90 °, the arm turning shaft 14 is oriented in the Z-axis direction, the tool changing arm 22 is on the lower side, and the used tool is returned to the tool magazine pot by the method described above.

Next, a second embodiment will be described with reference to FIG.
The only difference from the first embodiment (FIG. 1) is that the tool exchanging arm unit has two drive motors for rotating the tool exchanging arm, and each of the rotational force transmitting members. Since they are the same, the same parts are designated by the same reference numerals to avoid duplication of description, and the description will be omitted or simplified.

On the frame 61 of the tool change arm unit 11,
An NC drive insertion / removal servo motor 62 and a turning servo motor 63 are fixed in parallel with the reference numeral 14. A pulley 64 is fitted to the output shaft 62a of the inserting / pulling servo motor 62, and a synchro belt 66 is stretched between the pulley 64 and the pulley 65 fitted to the end of the rolled ball screw 33. Servo motor for turning 63
A pulley 67 is fitted to the output shaft 63a of the, and a pulley 69 is fitted to an end of an arm drive shaft 68 that is connected to the arm turning shaft 14 via a speed reducer 47 and a joint 48, and Pulley 67
A synchro belt 71 is stretched between and.

 Next, the operation of the second embodiment will be described.

After the cutting work by the tool attached to the spindle 7 is completed, the spindle sleeve 10 moves upward in the Z-axis direction and is positioned at the predetermined tool exchange position, and a tool exchange command is issued from the NC, and the carrier 9 moves to the spindle direction in the Y-axis direction. Then, when positioned at the tool exchange position on the left side of the spindle head 6, the empty gripper of the tool exchange arm 22 grips the spindle tool. Then, the tool pulling device is operated to release the clamp of the spindle tool, the servo motor 62 for insertion and removal is rotated by NC control, and the rolled ball screw 33 is rotated via the pulley 64, the synchro belt 66, and the pulley 65.
The tool changing arm 22 moves downward in the Z-axis direction to remove the spindle tool. When the withdrawal approaches the end and the risk of interference disappears, the rotation servomotor 63 starts to rotate under NC control, the arm rotation shaft 68 rotates via the pulley 67, the synchro belt 71, and the pulley 69, and the tool change arm 22 moves. The positions of both tools that swivel 180 ° and grip are switched. When the turning is near to the end and the danger of interference disappears, the reverse rotation of the insertion / removal servomotor 62 is started, the tool changing arm 22 moves upward in the Z-axis direction, and the next tool is inserted into the spindle 7. Next, after the next tool is clamped on the spindle 7 by the tool pulling device, the tool changing arm 22 is separated from the next tool by the movement of the carrier 9 to the tool magazine device 8 side.

Next, attach 90 ° angular attachment to the spindle sleeve 10.
When 51 is attached, the tool changing arm unit 11 in the standby state is turned 90 °, the arm turning shaft 14 faces the X-axis direction, and the tool changing arm 22 faces the front side. Exchange will take place.

Effect of the Invention Since the present invention is configured as described above, it has the following effects.

The tool exchanging arm unit according to claims 1 and 2 is provided with one NC control drive motor for swiveling and inserting / removing the tool exchanging arm, and is alternately connected to the swiveling side and the inserting / removing side by an electromagnetic clutch. By providing braking means on the road,
Since the tool change operation is controlled by NC, compared to the conventional hydraulic drive, heat is not generated, it is possible to escape from thermal displacement, accuracy and position at stop are stable, and the structure is simple. Therefore, space saving and cost reduction can be achieved. In addition, NC software can easily obtain the optimum operating speed of the tool change arm, enabling smooth movement without shock and shortening the tool change time.

In addition, the NC torque guard safety function improves durability against damage such as during a collision.

Since the tool change arm unit of claims 3 and 4 is provided with two NC control drive motors for turning and removing the tool change arm, the tool change operation is controlled by the NC. In addition to the effects of 1 and 2, it is possible to start the swiveling operation within the range where there is no interference during the tool removing operation, and it is possible to further shorten the tool replacement time.

[Brief description of drawings]

FIG. 1 is the first of the NC control tool change arm unit of the present invention.
Sectional view of the embodiment, FIG. 2 is a schematic view of a portal machining center, FIG. 3 is an explanatory view of a tool exchange operation for the main spindle of the machine, FIG. 4 is an explanatory view of a tool exchange operation for a 90 ° angular attachment main spindle, and FIG. Is a sectional view of a second embodiment of the NC control tool changing arm unit of the present invention, and FIG. 6 is a sectional view of a conventional tool changing arm unit. 8 …… Tool magazine device 9 …… Carrier 11 …… Tool exchange arm unit 22 …… Tool exchange arm 32 …… Electromagnetic tooth scratch 33 …… Rolled ball screw 62 …… Removal servomotor 63 …… Swivel servomotor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-228047 (JP, A) Actual development Sho-63-41436 (JP, U) Actual public Sho-47-36443 (JP, Y1)

Claims (3)

[Scope of utility model registration request] 1. An automatic tool changing device for automatically changing tools between a tool magazine device of an NC machine tool and a spindle by swiveling and inserting / removing a tool changing arm, wherein one servo controlled by the NC device rotates. A motor is provided, and switching means is provided for switching and transmitting the driving force of the servomotor between turning and inserting / removing of the tool exchanging arm, so that power is transmitted to each of the turning drive system path and the inserting / removing drive system path of the tool exchanging arm. In addition to the brake means that operate in addition to the NC
The device is equipped with a safety function that detects torque-up and zeros the torque of the motor by means of detecting a current value above the set value of the motor when an overload above the set value acts on the tool change arm. Characteristic NC control tool change arm unit. 2. An automatic tool changer for automatically changing tools by moving a carrier between a tool magazine device and a spindle of an NC machine tool and rotating and removing / inserting a tool changing arm, the rotation of which is controlled by the NC device. One servomotor is provided, a first gear and a second gear that transmit rotation are provided on an output axis of the servomotor, and a clutch that switches a transmission system path between the first gear and the second gear is provided. A first intermediate gear member that meshes with the first gear is attached to a ball screw that is rotatably supported, and a brake unit that applies a brake to the first intermediate gear member except when power is transmitted is provided.
A ball nut that is screwed into the ball screw and movable in the screw axis direction is provided, and a twin type tool change arm member that is connected to the ball nut and is movable in a direction parallel to the ball screw is provided. Brake means is provided for applying a brake to the drive shaft rotatably supported by mounting the second intermediate gear member to which rotation is transmitted, except when power is being transmitted.
A spline shaft that is spline-fitted to the tool exchange arm member and supported only for rotation is provided, and a reduction gear is provided between the spline shaft and the drive shaft of the second intermediate gear member to reduce and transmit rotation. The NC device is equipped with a safety function that detects torque-up and zeros the torque of the motor by means of detecting a current value above the set value of the motor when an overload above the set value acts on the tool change arm. NC control tool change arm unit. 3. An automatic tool exchanging device for automatically exchanging a tool by moving a carrier between a tool magazine device of an NC machine tool and a spindle and revolving the tool exchanging arm. A first servomotor that is rotationally controlled by an NC device is provided, and a drive shaft that is rotatably supported is provided by attaching a pulley that is connected to the output shaft pulley of the first servomotor with a timing belt, and is the same as the drive shaft. A spline shaft provided only for rotation on the axis is provided, and a speed reducer for decelerating and transmitting the rotation is provided between the spline shaft and the drive shaft, and rotation is controlled by an NC device for inserting / removing the tool exchange arm. A ball screw provided with a second servomotor, and a pulley connected to a pulley of an output shaft of the second servomotor by a timing belt is mounted and supported only for rotation. A ball nut that is screwed into the ball screw and is movable in the axial direction of the screw; and a twin-type tool exchange member that is coupled to the ball nut and that is fitted to the spline shaft and is movable in the axial direction. The NC device is equipped with a safety function that detects torque up and zeros the torque of the motor by means of detecting a current value above the set value of the motor when an overload above the set value acts on the tool change arm. NC control tool change arm unit.