JP2021091040A - Machine tool - Google Patents

Abstract

To provide a machine tool which suppresses deterioration of machining accuracy of a workpiece caused by bending of a tool due to gravity.SOLUTION: A machine tool includes: a first workpiece main shaft which holds a workpiece and can rotate the workpiece around a central axis 201 extending in a horizontal direction; a tool main shaft 121 which holds a tool T; a B-axis servo motor which is orthogonal to the central axis 201 and turns the tool main shaft 121 around a central axis 204 extending in a direction including at least a horizontal direction component; and a control section which controls the B-axis servo motor. The control section calculates a bending angle α of the tool T due to gravity and specifies correction amount α of a turning angle of the tool main shaft 121 corresponding to the bending angle α.SELECTED DRAWING: Figure 4

Description

The present invention relates to a machine tool.

For example, Japanese Patent Application Laid-Open No. 2014-161941 (Patent Document 1) describes a tool spindle that holds a machining tool and rotates the machining tool around a rotation axis, a tool spindle holder that supports the tool spindle, and a vertical tool. A processing apparatus including a motor that swivels and drives a tool spindle holder around a swivel shaft extending in a direction is disclosed. In the machining apparatus disclosed in Patent Document 1, the amount of deflection of the machining tool is estimated, and the rotation axis of the machining tool in the tool spindle holder is adjusted so that the angular deviation of the work surface of the work is offset.

Japanese Unexamined Patent Publication No. 2014-161941

The workpiece may be machined using a long tool such as a long boring bar. In such a case, the tool bends downward due to its own weight, so that the contact angle between the cutting edge of the tool and the work changes, which causes a problem that the machining accuracy of the work decreases.

Therefore, an object of the present invention is to solve the above-mentioned problems, and to provide a machine tool that suppresses a decrease in machining accuracy of a work due to bending of a tool due to gravity.

A machine tool according to the present invention includes a work spindle capable of holding a work and rotating the work around a first axis extending in the horizontal direction, a tool holding portion for holding a tool, and a first shaft. It includes a drive motor that rotates the tool holding unit around a second axis that is orthogonal and extends in a direction that includes at least a horizontal component, and a control unit that controls the drive motor. The control unit calculates the deflection angle of the tool due to gravity, and specifies the correction amount of the turning angle of the tool holding unit corresponding to the deflection angle.

According to the machine tool configured in this way, the tool holding portion is swiveled around the second axis so that the correction amount of the turning angle of the tool holding portion specified by the control unit is reflected. As a result, it is possible to prevent the contact angle between the cutting edge of the tool and the work from being changed due to the bending of the tool due to gravity, and the machining accuracy of the work from being lowered.

Further, preferably, the tool holding portion is a tool spindle capable of rotating the tool around a third axis orthogonal to the second axis.

According to the machine tool configured in this way, when the work is machined by the tool held on the tool spindle, it is possible to prevent the machining accuracy of the work from being lowered due to the bending of the tool due to gravity.

Further, preferably, the load applied to the tool in the direction of gravity is w (N / mm), the length of the tool is L (mm), the Young's modulus of the tool is E (GPa), and the moment of inertia of area of the tool is I (mm ^4). If) is, the control unit, the deflection angle of the tool by gravity alpha a (rad), identified by the formula α ⁼ wL 3 / 6EI.

According to the machine tool configured in this way, the bending angle of the tool due to gravity can be obtained based on a predetermined formula.

Further, preferably, the diameter D (mm) of the tool is input to the control unit. Control unit, the tool of the second moment I (mm ^4), is calculated by the equation of I = πD ^4/64.

According to the machine tool configured in this way, the user inputs the diameter of the tool to the control unit to obtain the moment of inertia of area of the tool required to calculate the deflection angle of the tool due to gravity. be able to.

Further, preferably, the material of the tool is input to the control unit. The control unit identifies the Young's modulus of the tool by comparing the input tool material with the relationship between the pre-stored material and the Young's modulus.

According to the machine tool configured in this way, the user inputs the material of the tool to the control unit to obtain the Young's modulus of the tool required to calculate the deflection angle of the tool due to gravity. it can.

Also preferably, the machine tool further comprises an acquisition unit that acquires a physical quantity that correlates with the load of the drive motor. The length of the tool is input to the control unit. The control unit calculates the load applied to the tool in the direction of gravity based on the physical quantity acquired by the acquisition unit and the length of the tool.

According to the machine tool configured in this way, the user inputs the length of the tool to the control unit, and the acquisition unit acquires the physical quantity that correlates with the load of the drive motor, so that the tool bends due to gravity. The load in the direction of gravity applied to the tool required to calculate the angle can be obtained.

More preferably, the machine tool further includes a moving mechanism that moves the tool holding portion in a direction that includes a vertical component. The control unit calculates a correction amount for the position of the tool holding unit in the vertical direction based on the deflection angle of the tool, and controls the moving mechanism unit according to the correction amount.

According to the machine tool configured in this way, by further correcting the position of the cutting edge of the tool in the vertical direction, it is more effectively suppressed that the machining accuracy of the work is lowered due to the bending of the tool due to gravity. it can.

As described above, according to the present invention, it is possible to provide a machine tool that suppresses a decrease in machining accuracy of a work due to bending of a tool due to gravity.

It is a front view which shows the machine tool in embodiment of this invention. FIG. 5 is a front view showing a state in which a machine tool in FIG. 1 is used to perform deep hole drilling in a work piece using a long tool. It is sectional drawing which shows the processing point of the work in the range surrounded by the alternate long and short dash line III in FIG. It is a front view which shows the bending phenomenon of the tool held on the tool spindle. It is a figure which shows the apparatus configuration concerning the control of the B-axis angle correction and the X-axis position correction of a tool spindle in FIG. It is a figure which shows the functional structure about the control of the B-axis angle correction and the X-axis position correction of a tool spindle in FIG. It is a figure for demonstrating the load in the gravitational direction applied to the tool when the B axis position of the tool spindle is an angle other than −90 ° (θ _{B> −90 °).} It is a figure for demonstrating the load in the gravitational direction applied to the tool when the B axis position of the tool spindle is an angle other than −90 ° (θ _{B <−90 °).}

Embodiments of the present invention will be described with reference to the drawings. In the drawings referred to below, the same or corresponding members are given the same number.

FIG. 1 is a front view showing a machine tool according to an embodiment of the present invention. In FIG. 1, the inside of the machine tool is shown by seeing through a cover body (splash guard) that forms the appearance of the machine tool.

With reference to FIG. 1, the machine tool 10 according to the present embodiment has a turning function in which a tool is brought into contact with a rotating work to process a work, and a milling function in which a rotating tool is brought into contact with a work to process a work. It is a multi-tasking machine with functions. The machine tool 10 is an NC (Numerically Control) machine tool in which various operations for machining a workpiece are automated by numerical control by a computer.

First, the overall structure of the machine tool 10 will be described. The machine tool 10 has a bed 136, a first work spindle 111, a second work spindle 116, a tool spindle (first tool post) 121, and a second tool post 131.

The bed 136 is a base member for supporting the first work spindle 111, the second work spindle 116, the tool spindle 121, the second tool post 131, and the like, and is installed on the floor surface of a factory or the like. The bed 136 is made of a metal such as cast iron.

The first work spindle 111 and the second work spindle 116 are configured to be able to hold the work. The first work spindle 111 and the second work spindle 116 are provided so as to face each other in the Z-axis direction extending in the horizontal direction. The first work spindle 111 and the second work spindle 116 are mainly provided for rotating the work during turning using a fixing tool. The first work spindle 111 is provided so as to be rotatable about a central axis 201 parallel to the Z axis. The second work spindle 116 is provided so as to be rotatable about a central axis 202 parallel to the Z axis. The first work spindle 111 and the second work spindle 116 are provided with a first chuck mechanism 113 and a second chuck mechanism 118 for gripping the work so as to be detachable, respectively.

The first work spindle 111 is fixed on the bed 136. The second work spindle 116 is provided so as to be movable in the Z-axis direction by various feed mechanisms, guide mechanisms, servomotors, and the like.

The machine tool 10 may have a tailstock for supporting the center of rotation of the work held by the first work spindle 111 instead of the second work spindle 116. In this case, the tailstock is provided at a position facing the first work spindle 111 in the Z-axis direction.

The tool spindle 121 and the second tool post 131 are configured to hold the tool. The tool spindle 121 is provided above the second tool post 131.

The tool spindle 121 is rotatably provided about a central axis 203 parallel to the X axis extending in the vertical direction. The tool spindle 121 is provided with a clamp mechanism (not shown) for holding the tool detachably.

The tool spindle 121 is further provided so as to be rotatable about a central axis 204 extending in the horizontal direction and parallel to the Y axis orthogonal to the Z axis direction (B-axis rotation). The turning range of the tool spindle 121 is, for example, a range of ± 120 ° with respect to the posture in which the spindle end surface 123 of the tool spindle 121 faces downward (the posture shown in FIG. 1).

The tool spindle 121 is supported on the bed 136 by a column or the like (not shown). The tool spindle 121 is provided so as to be movable in the X-axis direction, the Y-axis direction, and the Z-axis direction by various feed mechanisms, guide mechanisms, servomotors, and the like provided on the column and the like.

The second tool post 131 has a so-called turret type, and a plurality of tools are radially attached to perform swivel indexing.

More specifically, the second tool post 131 has a swivel portion 132. The swivel portion 132 is provided so as to be swivelable around a central axis 206 parallel to the Z axis. A tool holder for holding the tool is attached at a position spaced around the central axis 206 in the circumferential direction. When the swivel portion 132 swivels around the central axis 206, the tool held by the tool holder moves in the circumferential direction, and the tool used for machining the work is determined.

The second tool post 131 is supported on the bed 136 by a saddle or the like (not shown). The second tool post 131 is provided so as to be movable in the X-axis direction and the Z-axis direction by various feed mechanisms, guide mechanisms, servomotors, and the like provided on the saddle and the like. The second tool post 131 may be provided so as to be movable in the Z-axis direction and the diagonally upward direction including the vertical component at right angles to the Z-axis direction.

A rotary tool may be held or a fixing tool may be held in each of the tool spindle 121 and the second tool post 131. The rotary tool is a tool for machining a workpiece while rotating, and is a drill, an end mill, a reamer, or the like. The fixing tool is a tool for processing a rotating workpiece, and is an inner diameter cutting tool including a long boring bar described later. When the rotary tool is held on the second turret 131, the second turret 131 incorporates a motor that outputs rotation and a power transmission mechanism that transmits the rotation output from the motor to the rotary tool.

The machine tool 10 further includes a splash guard 210. The splash guard 210 has the appearance of the machine tool 10 and forms a processing area 200 for the work.

The machine tool 10 further includes a B-axis servomotor 61 and an X-axis servomotor 63 (see FIG. 5 below). The B-axis servomotor 61 is a servomotor for turning the B-axis of the tool spindle 121, and turns the tool spindle 121 around the central axis 204. The X-axis servomotor 63 is a servomotor for moving the tool spindle 121 on the X-axis, and moves the tool spindle 121 in the X-axis direction (vertical direction).

Although not shown in FIG. 1, an automatic tool changer (ATC: Automatic Tool Changer) for automatically changing the tool mounted on the tool spindle 121 is provided around the first work spindle 111. A tool magazine for accommodating a replacement tool to be mounted on the tool spindle 121 is provided.

FIG. 2 is a front view showing a state in which a machine tool in FIG. 1 is used to perform deep hole drilling in a work using a long tool. FIG. 3 is a cross-sectional view showing the processing points of the workpiece in the range surrounded by the alternate long and short dash line III in FIG.

With reference to FIGS. 2 and 3, the machine tool 10 further includes a steady rest device 141 for preventing runout of the workpiece. The steady rest device 141 is attached to the swivel portion 132 of the second tool post 131. With such a configuration, the steady rest device 141 is provided so as to be movable in the X-axis direction and the Z-axis direction.

The work W is held by the first work spindle 111. The work W is supported by the steady rest device 141 at a position separated from the first chuck mechanism 113 in the Z-axis direction (+ Z-axis direction).

The tool spindle 121 is arranged at a position facing the first work spindle 111 in the Z-axis direction. The tool spindle 121 is swiveled (B-axis swivel) by an angle of −90 ° about the central shaft 204 from the reference posture shown in FIG. A long tool T such as a long boring bar is held by the tool spindle 121. The tool T projects from the spindle end surface 123 of the tool spindle 121 toward the work W in the Z-axis direction (−Z-axis direction).

The tool T as a whole has a cylindrical shape centered on the central axis 203. The tool T has a shaft portion 153 and a tip (blade portion) 151. The shaft portion 153 has a shaft shape having a circular cross section extending along the central shaft 203. A tip 151 is attached to the tip of the shaft portion 153. While rotating the work W held by the first work spindle 111 about the central shaft 201, the cutting edge 152 (tip portion of the tip 151) of the tool T held by the tool spindle 121 is brought into contact with the work W, and further, the tool. Deep holes are drilled in the work W by sending T toward the work W in the Z-axis direction.

FIG. 4 is a front view showing a bending phenomenon of the tool held on the tool spindle. When machining a work using a long tool T such as a long boring bar with reference to FIG. 4, the tool T may bend downward due to its own gravity.

In the figure before correction shown in the upper part of FIG. 4, the tool T, which should originally extend along the central axis 203 of the tool spindle 121, flexes so as to extend along the central axis 203T shifted downward from the central axis 203. I'm sorry. The angle α formed by the central shaft 203 and the central shaft 203T at the cutting edge position of the tool T is the bending angle of the tool T. In this case, since the contact angle between the cutting edge of the tool T and the work changes, the machining accuracy of the work decreases.

On the other hand, in the corrected figure shown in the lower part of FIG. 4, the B-axis angle is corrected by turning the tool spindle 121 around the central axis 204 by an angle α corresponding to the deflection angle α. ing. The tip of the tool T that bends along the central axis 203T due to the correction of the B-axis angle is arranged parallel to the central axis 203. As a result, the contact angle between the cutting edge of the tool T and the work is maintained, so that it is possible to suppress a decrease in machining accuracy of the work due to bending of the tool due to gravity.

Further, the correction of the B-axis angle of the tool spindle 121 causes a deviation in the X-axis direction (vertical direction) at the tip of the tool T. On the other hand, the position of the tool spindle 121 in the X-axis direction is corrected by moving the tool spindle 121 by the correction amount H in the X-axis direction. The tip of the tool T that bends along the central axis 203T due to the correction of the position in the X-axis direction overlaps with the central axis 203. As a result, the contact position between the cutting edge of the tool T and the work in the X-axis direction is maintained, so that it is possible to more effectively suppress a decrease in machining accuracy of the work due to bending of the tool due to gravity.

Subsequently, a control method of correction of the B-axis angle of the tool spindle 121 (B-axis angle correction) and correction of the position of the tool spindle 121 in the X-axis direction (X-axis position correction) will be described.

FIG. 5 is a diagram showing a device configuration related to control of B-axis angle correction and X-axis position correction of the tool spindle in FIG. FIG. 6 is a diagram showing a functional configuration related to control of B-axis angle correction and X-axis position correction of the tool spindle in FIG.

First, a method of controlling the B-axis angle correction of the tool spindle 121 will be described with reference to FIGS. 5 and 6. The machine tool 10 further includes a control unit 50, an input unit 52, a storage unit 76, and an acquisition unit 77.

The control unit 50 controls the operation of the machine tool 10 including the tool spindle 121. The control unit 50 calculates the deflection angle α of the tool T due to gravity, and specifies the correction amount α of the turning angle of the tool spindle 121 corresponding to the deflection angle. The control unit 50 controls the B-axis servomotor 61 according to the correction amount α of the turning angle of the tool spindle 121.

The input unit 52 receives input of various commands or information by the operator of the machine tool 10. The input unit 52 receives input of the material of the tool T, the length L (mm) of the tool, and the diameter D (mm) of the tool by the operator of the machine tool 10. The input unit 52 outputs the input material of the tool T, the length L (mm) of the tool, and the diameter D (mm) of the tool to the control unit 50.

In the present embodiment, the length L (mm) of the tool T is approximately defined as the length from the spindle end face 123 of the tool spindle 121 in the Z-axis direction to the cutting edge 152 (tip portion of the tip 151) of the tool T. be able to. Further, the diameter D (mm) of the tool T can be approximately defined as the diameter of the shaft portion 153 of the tool T.

As a typical example, the input unit 52 is provided on the operation panel of the machine tool 10. The input unit 52 is composed of, for example, a touch panel type operation panel, a switch, or another input interface.

The storage unit 76 stores the relationship between the material of the tool T and Young's modulus. The storage unit 76 stores a plurality of materials (steel types) that can be candidates for the material of the tool T and Young's modulus of each material. The storage unit 76 is composed of, for example, a flash memory.

The acquisition unit 77 acquires a physical quantity that correlates with the load of the B-axis servomotor 61. The acquisition unit 77 includes an ammeter and acquires the current value of the B-axis servomotor 61. The acquisition unit 77 automatically acquires the current value of the B-axis servomotor 61 when, for example, the tool T is mounted on the tool spindle 121 by ATC and the tool spindle 121 is swiveled by the B-axis at an angle of −90 °. You may. The acquisition unit 77 outputs the acquired current value of the B-axis servomotor 61 to the control unit 50.

The control unit 50 has a CPU (Central Processing Unit) 51. The CPU 51 uses the material of the tool T, the length of the tool, and the diameter of the tool input from the input unit 52 to the control unit 50, and the current value of the B-axis servomotor 61 input from the acquisition unit 77 to the control unit 50. It is used to calculate the deflection angle α of the tool T due to gravity.

The CPU 51 may be provided on the operation panel of the machine tool 10 together with the input unit 52, or may be provided on the control panel of the machine tool 10.

More specifically, the CPU 51 includes a Young's modulus specifying unit 71, a moment of inertia of area calculation unit 72, a load calculation unit 73, and a deflection angle calculation unit 81.

The geometrical moment of inertia calculation unit 72 calculates the geometrical moment of inertia I (mm ⁴ ) of the tool T by the following (Equation 1).
I = πD ^4/64 (Equation 1)
The Young's modulus specifying unit 71 compares the material of the tool T input to the CPU 51 through the input unit 52 with the relationship between the material stored in the storage unit 76 and the Young's modulus, whereby the Young's modulus E (GPa) of the tool T is compared. ) Is specified.

The load calculation unit 73 is based on the current value of the B-axis servomotor 61 (load of the B-axis servomotor 61) and the length L (mm) of the tool T, and the load w (N) in the gravity direction applied to the tool T. / Mm) is calculated.

The geometrical moment of inertia calculation unit 72 outputs the calculated geometrical moment of inertia I (mm ⁴ ) of the tool T to the deflection angle calculation unit 81. The Young's modulus specifying unit 71 outputs the Young's modulus E (GPa) of the specified tool T to the deflection angle calculation unit 81. The load calculation unit 73 outputs the calculated load w (N / mm) in the gravity direction applied to the tool T to the deflection angle calculation unit 81.

The deflection angle calculation unit 81 calculates the deflection angle α (rad) of the tool T due to gravity according to the following (Equation 2).
α ⁼ wL 3 / 6EI (Equation 2)
The deflection angle calculation unit 81 has the length L (mm) of the tool T input from the input unit 52 and the geometrical moment of inertia input unit 72 of the tool T input to the above (Equation 2). The value of the moment I (mm ⁴ ), the value of the Young's modulus E (GPa) of the tool T input from the Young's modulus specifying unit 71, and the load w in the gravity direction applied to the tool T input from the load calculation unit 73 ( By substituting the value of N / mm), the deflection angle α (rad) of the tool T due to gravity is calculated.

The deflection angle calculation unit 81 outputs a correction amount α of the turning angle of the tool spindle 121 corresponding to the calculated deflection angle α of the tool T due to gravity to the PLC 54 and the X-axis correction amount calculation unit 82, which will be described later.

The control unit 50 further includes a PLC (Programmable Logic Controller) 54 and a first servo driver 56.

The PLC 54 controls various units in the machine tool 10 according to a PLC program prepared in advance. The PLC program is described by, for example, a ladder program. The PLC 54 sends a control command to the first servo driver 56 based on the correction amount α of the turning angle of the tool spindle 121. The first servo driver 56 receives an input of a target position from the PLC 54 and controls the B-axis servomotor 61.

Next, the control of the X-axis position correction of the tool spindle 121 will be described. The control unit 50 calculates a correction amount H of the position of the tool spindle 121 in the vertical direction based on the deflection angle α of the tool T, and controls the X-axis servomotor 63 according to the correction amount H.

More specifically, the CPU 51 further includes an X-axis correction amount calculation unit 82. The X-axis correction amount calculation unit 82 calculates the correction amount H of the position of the tool spindle 121 in the X-axis direction (vertical direction) by the following (Equation 3). In (Equation 3), the coordinates in the −Z axis direction with respect to the spindle end surface 123 of the tool spindle 121 are shown as the l (L) axis.

The X-axis correction amount calculation unit 82 outputs the calculated correction amount H of the position of the tool spindle 121 to the PLC 54.

The control unit 50 further includes a second servo driver 57. The PLC 54 sends a control command to the second servo driver 57 based on the correction amount H of the position of the tool spindle 121. The second servo driver 57 receives the input of the target position from the PLC 54 and controls the X-axis servomotor 63.

According to such a configuration, the B-axis angle of the tool spindle 121 reflects the correction amount α of the turning angle of the tool spindle 121 corresponding to the deflection angle α of the tool T due to gravity, thereby causing the tool T to bend due to gravity. It is possible to suppress a change in the contact angle between the cutting edge of the tool T and the work due to the above. Further, the B-axis angle of the tool spindle 121 is reflected in the position of the tool spindle 121 in the X-axis direction by reflecting the correction amount H of the position of the tool spindle 121 in the vertical direction calculated based on the deflection angle α of the tool T. It is possible to eliminate the misalignment of the cutting edge of the tool in the X-axis direction caused by the correction of. Therefore, according to the machine tool 10 in the present embodiment, it is possible to effectively suppress a decrease in machining accuracy of the work due to bending of the tool T due to gravity.

7 and 8 are diagrams for explaining the load in the gravity direction applied to the tool when the B-axis position of the tool spindle is at an angle other than −90 °.

With reference to FIG. 7, the _{case where the B-axis position θ B} of the tool spindle 121 is smaller than −90 ° (θ _B > −90 °) is shown in the drawing. In this case, instead of the load w in the gravity direction applied to the tool T in the above (Equation 2), the _{load w V} calculated by the formula _{w V} = w × sin (−θ _B ) may be used.

With reference to FIG. 8, the _{case where the B-axis position θ B} of the tool spindle 121 is larger than −90 ° (θ _B <−90 °) is shown in the drawing. In this case, if the _{load w V} calculated by the formula _{w V} = w × cos (−θ _B −90 °) is used instead of the load w in the gravity direction applied to the tool T in the above (Equation 2). Good.

Further, when the work is processed using the second work spindle 116 in FIG. 1, −θ _B in the above equation may be replaced with + θ _B.

In the present embodiment, the case where the tool holding portion in the present invention is the tool spindle for rotating the rotary tool has been described, but the present invention is not limited to this. The tool holding portion in the present invention may be, for example, a tool post for holding a fixed tool.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

The present invention is mainly applied to a machine tool capable of performing workpiece machining using a long tool.

10 Machine tool, 50 Control unit, 52 Input unit, 56 1st servo driver, 57 2nd servo driver, 61 B-axis servo motor, 63 X-axis servo motor, 71 Young rate identification unit, 72 Cross section secondary moment calculation unit, 73 Load calculation unit, 76 Storage unit, 77 Acquisition unit, 81 Deflection angle calculation unit, 82 X-axis correction amount calculation unit, 111 1st work spindle, 113 1st chuck mechanism, 116 2nd work spindle, 118 2nd chuck mechanism , 121 Tool spindle, 123 Spindle end face, 131 Second tool post, 132 Swivel part, 136 bed, 141 steady rest device, 151 chip, 152 cutting edge, 153 shaft part, 200 machining area, 201, 202, 203, 203T, 204 , 206 central axis, 210 splash guard.

Claims (7)

A work spindle capable of holding the work and rotating the work around a first axis extending in the horizontal direction,
The tool holding part that holds the tool and
A drive motor that rotates the tool holding portion around a second axis that is orthogonal to the first axis and extends in a direction that includes at least a horizontal component.
A control unit that controls the drive motor is provided.
The control unit is a machine tool that calculates the deflection angle of the tool due to gravity and specifies the correction amount of the turning angle of the tool holding unit corresponding to the deflection angle. The machine tool according to claim 1, wherein the tool holding portion is a tool spindle capable of rotating the tool around a third axis orthogonal to the second axis. The load in the gravity direction applied to the tool is w (N / mm), the length of the tool is L (mm), the Young's modulus of the tool is E (GPa), and the moment of inertia of area of the tool is I (mm ^4). ),
Wherein the control unit, the deflection angle of the tool by gravity alpha a (rad), identified by the formula α ⁼ wL 3 / 6EI, machine tool according to claim 1 or 2. The diameter D (mm) of the tool is input to the control unit.
Wherein the control unit, the tool of the second moment I (mm ^4), is calculated by the equation of I = πD ^4/64, machine tool according to claim 3. The material of the tool is input to the control unit.
The machine tool according to claim 3 or 4, wherein the control unit specifies the Young's modulus of the tool by comparing the input material of the tool with the relationship between the material stored in advance and Young's modulus. .. An acquisition unit that acquires a physical quantity that correlates with the load of the drive motor is further provided.
The length of the tool is input to the control unit.
The control unit calculates the load in the gravity direction applied to the tool based on the physical quantity acquired by the acquisition unit and the length of the tool, according to any one of claims 3 to 5. Machine Tools. Further provided with a moving mechanism portion for moving the tool holding portion in a direction including a vertical component, the tool holding portion is further provided.
Any one of claims 1 to 6, wherein the control unit calculates a correction amount of the position of the tool holding unit in the vertical direction based on the deflection angle of the tool, and controls the movement mechanism unit according to the correction amount. The machine tool according to item 1.

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