Spindle unit of a machine tool

Abstract

This invention provides a spindle mechanism for a machine tool that solves the problem of the tool becoming stuck to the spindle, in a machine tool spindle mechanism with an electrically operated tool unclamping mechanism. [Solution] The spindle control unit has a tool unclamping control unit 16 that increases the motor output and performs the tool unclamping operation again if the tool unclamping operation is not performed properly even when the motor is operated at a preset output.

Description

Technical Field

[0005]

[0001] This invention relates to a spindle device of a machine tool, and more particularly to a spindle device of a machine tool having a tool clamping / unclamping function.

Background Art

[0002] A spindle device of this type of machine tool includes a hollow spindle, a tool holding part (e.g., a collet) that clamps / unclamps a tool mounted on the spindle, a power transmission part (drawbar, disc spring, etc.) that operates the tool holding part on the clamping side and the unclamping side, a drive part that drives the power transmission part, and a spindle control part that controls the spindle. In a conventional spindle device of a machine tool, it is well known that a hydraulic cylinder is used as the drive part. During unclamping, the piston is advanced by the hydraulic cylinder to compress the disc spring and push the drawbar toward the tool side. During clamping, the piston is retracted to allow the drawbar to move in the clamping direction by the elastic force of the disc spring.

[0003] In recent years, there has been an increasing demand to replace the drive part from hydraulic drive to electric drive in terms of decarbonization and environmental considerations. To meet this demand, Patent Document 1 discloses, as a tool unclamping device in a spindle device of a machine tool, a spindle to which a tool for machining a workpiece is mounted at an end, an output shaft provided movably in the axial direction with respect to the spindle and pressing the tool to be in an unclamped state, an electric motor capable of generating power to put the tool in an unclamped state, a power transmission mechanism capable of transmitting the power from the electric motor to the output shaft, and a detection part for detecting the amount of current supplied to the electric motor.

[0004] According to the spindle device of the machine tool in Patent Document 1, by not using hydraulic pressure, maintenance such as replacement of hydraulic oil, oil supply, and handling of leaked oil is unnecessary, and there is no need to treat waste oil, so the environmental load can be reduced. Also, by electrifying the hydraulic pressure, the quietness is enhanced and accurate control with high precision becomes possible.

[0005] According to Patent Document 1, motorizing the spindle tool unclamping enables unclamping without the use of hydraulics. However, even with motorization, there was a problem in that the tool could become stuck to the spindle, making unclamping impossible.

[0006] In other words, the clamped tool may stick to the spindle tapered surface due to the effects of cutting fluid, dust, etc. in the machine's operating environment, and the load and stroke applied to the disc spring set in the factory settings may cause the tool to become fixed to the spindle and unable to be unclamped, a problem that conventional systems could not address.

[0007] Patent Document 2 discloses reducing the speed at which the tool is pulled out after unclamping in order to mitigate the impact when the tool becomes stuck to the spindle. However, it does not describe changing how force is applied to the disc spring, and even when combined with Patent Document 1, it is not possible to resolve the problem of the tool becoming stuck to the spindle at the time of unclamping. Furthermore, since the determination of whether the tool is stuck to the spindle is based on the spindle's stopping time, there is a possibility that the speed at which the tool is pulled out will be reduced even when the tool is not actually stuck, and there is room for improvement in order to improve productivity. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2009-018353 [Patent Document 2] Japanese Patent Publication No. 2021-024000 [Overview of the project] [Problems that the invention aims to solve]

[0009] In view of the above circumstances, the object of this invention is to provide a spindle device for a machine tool that solves the problem of the tool becoming stuck to the spindle in a spindle device for a machine tool in which the tool unclamping is motorized. [Means for solving the problem]

[0010] To achieve the above objective, the present invention comprises the following embodiments.

[0011] 1) A spindle device for a machine tool comprising a spindle, a tool holding unit for clamping / unclamping a tool mounted on the spindle, a power transmission unit for operating the tool holding unit, a drive unit for driving the power transmission unit, and a spindle control unit for controlling the spindle, wherein the spindle control unit has a tool unclamping control unit that increases the output of the drive unit to perform the unclamping operation of the tool again if the unclamping operation of the tool is not performed normally even when the drive unit is operated with a preset output.

[0012] 2) The spindle apparatus for a machine tool according to 1) above, wherein the drive unit is a motor, the power transmission unit has a drawbar that is moved by the drive unit, and the tool unclamping control unit performs an unclamping operation of the tool by changing the speed or acceleration of the power transmission unit when a motor torque greater than a preset threshold is generated, thereby changing the force acting on the tool when the drawbar and the tool collide.

[0013] 3) The spindle device for a machine tool as described in 1) above, wherein the power transmission unit includes a ball screw rotated by power from the drive unit, a pusher whose position is variable by the rotation of the ball screw, a drawbar moved by the pusher, and a disc spring interposed between the spindle and the drawbar to bias the drawbar toward the clamping side, a detection device for detecting the attachment / detachment state of the tool is provided near the tool holding unit, and the tool unclamping control unit, when the unclamping of the tool cannot be detected by the detection device during the unclamping operation of the tool, further increases the stroke amount of the pusher which has been set in advance, and performs the unclamping operation of the tool.

[0014] 4) The spindle device of a machine tool as described in 3) above, characterized in that, if the tool cannot be removed even after performing the unclamping operation of the tool multiple times, the tool unclamping operation of the tool is performed by changing the speed at which the pusher pushes the disc spring from the previous speed. [Effects of the Invention]

[0015] According to the spindle device of the machine tool described in 1) above, the tool unclamping operation is normally performed by operating the drive unit with a preset output. If the tool becomes stuck to the spindle and the tool unclamping operation is not performed normally, the tool unclamping control unit increases the output of the drive unit to perform the tool unclamping operation again. To detect that the tool has become stuck to the spindle, for example, an appropriate detection device may be installed near the tool, or if the drive unit is a motor, it may be configured to detect abnormalities in motor torque. When it is detected that the tool has become stuck to the spindle, an automatic recovery operation is performed by increasing the output of the drive unit (for example, the thrust of the pusher that pushes the disc spring that provides elastic force for clamping the tool, the stroke, etc.). In this way, the state in which the tool is stuck to the spindle can be resolved, and machine stoppage can be avoided.

[0016] According to the spindle device of the machine tool described in 2) above, when the drive unit is a motor, the system is configured to automatically reset the power transmission unit when an abnormality in motor torque is detected. In the automatic reset operation, the speed or acceleration at which the power transmission unit operates is changed, thereby changing the force acting on the tool when the drawbar and the tool collide, and thus the tool can be easily unclamped. To change the speed or acceleration at which the power transmission unit operates, for example, this can be done based on a thrust waveform set so that the thrust applied to the drawbar changes over time.

[0017] According to the spindle device of the machine tool in 3) above, instead of detecting an abnormality in the motor torque, it is possible to reliably detect the unclamping of the tool by using a detection device that detects the attachment / detachment state of the tool. The stroke of the pusher is setable, and by further expanding the preset stroke amount of the pusher, it is possible to reliably unclamp the tool.

[0018] According to the spindle device of the machine tool in 4) above, the thrust, thrust waveform, and stroke of the pusher during automatic recovery are set to have multiple patterns. When the tool cannot be removed even after performing the unclamping operation of the tool multiple times, by changing the speed at which the pusher presses the disc spring from the previous speed and executing the unclamping operation of the tool, it is possible to more reliably unclamp the tool.

Brief Description of the Drawings

[0019] [Figure 1] This is a diagram schematically showing an embodiment of the spindle device of the machine tool of this invention, showing the clamped state of the tool. [Figure 2] This is a diagram showing the state shifted from the clamped state in FIG. 1 to the unclamped state. [Figure 3] This is a block diagram explaining the operation sequence in the tool unclamping control unit. [Figure 4] This is a flowchart of the operation sequence in the tool unclamping control unit. [Figure 5] This is a diagram showing an example of a thrust waveform suitable for clamping the tool.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of this invention will be described with reference to the drawings. FIG. 1 shows the clamped state of the tool, and FIG. 2 shows the unclamped state of the tool. In the following description, the left side of FIGS. 1 and 2 is taken as the front, and the right side as the rear.

[0021] As shown in FIGS. 1 and 2, the spindle device (1) of a machine tool includes a hollow spindle (2) to which a tool (T) for machining a workpiece is detachably attached, a collet (3) as a tool holding part for clamping / unclamping the tool (T) attached to the spindle (2), a power transmission part (4) for operating the collet (3) on the clamping side and the unclamping side, an electric motor (5) as a driving part for driving the power transmission part (4), and a spindle control part (not shown) for controlling the spindle (2).

[0022] The power transmission part (4) includes a ball screw (11) rotated by the power of the motor (5) via a reduction mechanism (12), a pusher (13) whose position is variable by the rotation of the ball screw (11), a drawbar (14) moved to the clamping side or the unclamping side as the pusher (13) moves in the front-rear direction, and a disc spring (15) interposed between the spindle (2) and the drawbar (14) to bias the drawbar (14) to the clamping side.

[0023] Although not shown in the figure, the spindle (2) is rotatably supported in a cylindrical housing via a plurality of bearings. The collet (3) is disposed at the front end of the drawbar (14), holds the pull stud bolt (T1) of the tool (T) by closing as the drawbar (14) retreats, and releases the holding of the pull stud bolt (T1) of the tool (T) by opening as the drawbar (14) advances. The pusher (13) is fixed to a ball screw nut (11a) linearly moved by the rotation of the ball screw (11). The disc spring (15) is held by a spring receiver (2a) fixed to the spindle (2) and a spring receiver (14a) fixed to the drawbar (14).

[0024] In Figure 1, the pusher (13) is in a retracted position away from the drawbar (14), allowing the drawbar (14) to move in the clamping direction due to the elastic force of the disc spring (15). Therefore, the drawbar (14) is positioned rearward (towards the clamping side) by being biased by the disc spring (15), and as a result, the tool (T) is in a clamped state held by the collet (3).

[0025] In the state shown in Figure 1, when the motor (5) is driven, the ball screw (11) rotates, and the pusher (13) moves forward together with the ball screw nut (11a). Consequently, the drawbar (14) is moved forward (towards the unclamping side) against the elastic force of the disc spring (15).

[0026] As a result, as shown in Figure 2, the disc spring (15) is compressed, and the tool (T) is in an unclamped state, not held by the collet (3). The tool (T) is pushed by the drawbar (14), so that (whereas in Figure 1 the rear surface of the flange portion (T2) of the tool (T) and the front end surface (2b) of the spindle (2) are flush,) the rear surface of the flange portion (T2) of the tool (T) is separated from the front end surface (2b) of the spindle (2). In the state shown in Figure 2, the tool (T) is movable forward, and the used tool (T) can be replaced with a new tool by an automatic tool changer (not shown).

[0027] According to the spindle unit (1) of the machine tool described above, the drawbar (14) is normally moved by operating the motor (5) as the drive unit with a preset output, and the unclamping operation of the tool (T) can be performed normally.

[0028] Here, the spindle unit (1) of the machine tool described above differs from conventional systems that move the drawbar using a hydraulic cylinder, in that it moves the drawbar (14) using an electric motor (5). The motor (5) has many advantages compared to a hydraulic cylinder.

[0029] Therefore, in the spindle unit (1) of this machine tool, a tool unclamping control unit (16) having the operation sequence shown in Figures 3 and 4 is added to the conventional spindle control unit.

[0030] As an example of an operation sequence performed by the tool unclamping control unit (16), as shown in the block diagram in Figure 3, the following operations are performed: (1) abnormality detection by motor torque, (2) transition to automatic recovery operation, (3) change of thrust of pusher (13) and / or change of stroke of pusher (13) as automatic recovery operation, (4) confirmation of the movement stroke of pusher (13) as confirmation of operation completion, (5) repetition of automatic recovery operation and operation completion confirmation if operation completion confirmation is NG, and (6) transition to normal operation if operation completion confirmation is OK.

[0031] Figure 4 shows a flowchart illustrating the more detailed steps of the operation sequence of the tool unclamping control unit (16).

[0032] In tool unclamping control, as shown in Figure 4, first, an unclamping operation of the tool (T) is performed to change it from the state in Figure 1 to the state in Figure 2 (S1). At this time, the torque value of the motor (5) in the state in Figure 2 is acquired (S2), and it is determined whether the torque value is normal (S3). Normally, if the torque value is determined to be normal, the operation is completed (the next operation such as automatic tool change is performed) assuming that the tool (T) has been properly unclamped. If the torque value is not normal in step (S3), it is considered that the tool (T) is stuck to the spindle (2), so the automatic recovery operation from step (S4) onward is performed.

[0033] In the automatic recovery operation, as the first automatic recovery operation, the upper limit of the torque of the motor (5) is changed to change the thrust (increase the thrust), and the stroke of the pusher (13) is also changed (increased) to increase the output (torque and / or rotational speed) of the motor (5) for unclamping (S4). Under these conditions, the unclamping operation of the tool (T) is performed (S5), the stroke of the pusher (13) is checked (S6), and it is determined whether the tool (T) is stuck (S7). If it is determined in step (S7) that the tool (T) is not stuck, the operation is completed (the next operation such as automatic tool change is initiated) as having been properly unclamped of the tool (T).

[0034] In step (S7), if it is determined that the tool (T) is stuck, a second automatic recovery operation is performed to increase the output of the motor (5) for unclamping by changing the operating pattern (thrust waveform) of the motor (5) and changing (increasing) the stroke of the pusher (13) (S8). Under these conditions, the unclamping operation of the tool (T) is performed again (S5), the stroke of the pusher (13) is checked (S6), and it is determined whether the tool (T) is stuck (S7). The second automatic recovery operation is performed until it is determined in step (S7) that the tool (T) is not stuck.

[0035] According to the above embodiment, in a spindle device (1) having a motor (5) as a drive unit and a reduction mechanism (12), by controlling the output (torque and / or rotational speed) of the motor (5), the thrust of the pusher (13) applied to the drawbar (14) (change in pusher thrust over time, shown as a thrust waveform) and the stroke of the pusher (13) can be optimized to properly unclam the tool (T).

[0036] The thrust (thrust waveform) applied to the drawbar (14) may be, for example, as shown in Figure 5(a), based on the initial upper limit of the torque of the motor (5) shown by the dashed line (equal to the initial setting value of the thrust of the pusher (13)), the upper limit of the maximum torque of the motor (5) (thrust of the pusher (13)) is increased, and a load is applied to the disc spring (15) at high speed to unclam the tool (T). Alternatively, as shown in Figure 5(b), based on the initial upper limit of the torque of the motor (5) shown by the dashed line (equal to the initial setting value of the thrust of the pusher (13)), the upper limit of the maximum torque of the motor (5) (thrust of the pusher (13)) is increased, and the force acting on the disc spring (15) is gradually increased to unclam the tool (T). Although not shown in the diagram, in Figures 5(a) and 5(b), the thrust can be increased or decreased not only linearly, but also exponentially or using a power function.

[0037] In Figures 1 and 2 of the above embodiment, a tool (T) with a BT shank and a pull stud bolt (T1) is shown. However, the shank shape of the tool is not limited to that shown, and known components can be used as appropriate for the tool (T), tool holder (3), and power transmission unit (4).

[0038] Furthermore, in the above embodiment, the torque of the motor (5) is monitored, and if an abnormal torque is detected, it is determined that the tool (T) is stuck to the spindle (2). However, whether or not the tool (T) is stuck to the spindle (2) may be determined, for example, by providing a detection device near the collet (3) to detect the attachment / detachment status of the tool (T). In this case, it becomes unnecessary to acquire the torque value of the motor (5) and to determine whether the torque value of the motor (5) is normal, and the determination of whether or not the tool is stuck is made based on the detection result of the attachment / detachment status of the tool (T) by the detection device. [Explanation of Symbols]

[0039] (1): Spindle unit of a machine tool (2):Spindle (3): Collet (tool holder) (4): Power transmission section (5): Motor (drive unit) (11): Ball screw (13): Pusher (14): Drawbar (15): Disc spring (16): Tool unclamping control unit (T):Tool

Claims

1. A spindle device for a machine tool comprising a spindle, a tool holding unit for clamping / unclamping a tool mounted on the spindle, a power transmission unit for operating the tool holding unit, a drive unit for driving the power transmission unit, and a spindle control unit for controlling the spindle, wherein the spindle control unit has a tool unclamping control unit that increases the output of the drive unit to perform the unclamping operation of the tool again if the unclamping operation of the tool is not performed normally even when the drive unit is operated with a preset output.

2. The spindle device of a machine tool according to claim 1, characterized in that the drive unit is a motor, the power transmission unit has a drawbar that is moved by the drive unit, and the tool unclamping control unit changes the speed or acceleration of the power transmission unit when a motor torque greater than a preset threshold is generated, thereby changing the force acting on the tool when the drawbar and the tool collide, and thereby performing an unclamping operation on the tool.

3. The power transmission unit comprises a ball screw rotated by power from the drive unit, a pusher whose position is variable by the rotation of the ball screw, a drawbar moved by the pusher, and a disc spring interposed between the spindle and the drawbar to bias the drawbar toward the clamping side, a detection device for detecting the attachment / detachment state of the tool is provided near the tool holding unit, and the tool unclamping control unit, when the unclamping of the tool cannot be detected by the detection device during the unclamping operation of the tool, further increases the stroke amount of the pusher which has been set in advance, and performs the unclamping operation of the tool, as described in claim 1.

4. The spindle device of a machine tool according to claim 3, characterized in that, if the tool cannot be removed even after performing the unclamping operation of the tool multiple times, the tool unclamping control unit changes the speed at which the pusher pushes the disc spring from the previous speed to perform the unclamping operation of the tool.

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