Machine tool

Abstract

To provide a machine tool that notifies an operator of the maximum command rotational speed or allowable rotational speed at which a machining error caused by vibration due to an unbalanced load does not deviate from a permissible range, prior to machining.SOLUTION: A machine tool 100 that performs turning processing by rotating a workpiece W, includes: a workpiece rotation device 106 including a workpiece mounting unit 120 for mounting the workpiece and a rotation motor Mb for rotating the workpiece mounting unit; a control device 140 that calculates the allowable rotational speed of the workpiece rotation device on the basis of a change amount in torque of the rotation motor when the workpiece rotation device mounted with the workpiece is rotated; and a display device 142 that displays the allowable rotational speed of the workpiece rotation device calculated by the control device.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a machine tool that calculates the allowable rotational speed of a rotating device based on the amount of change in torque of a rotary motor when the rotating device with a workpiece attached is rotated. [Background technology]

[0002] When a workpiece is attached to a rotating device, rotated, and turned with a cutting tool, vibrations may occur due to an unbalanced load acting on the rotating device. In order to prevent this, the invention in Patent Document 1 describes a method for correcting torque imbalance in a workpiece, which determines the imbalance from the torque change of the drive motor when the workpiece is rotated, and specifies the mass and position of a counterweight added to a balance table or the cutting mass and cutting position in order to correct the imbalance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-061918 A Summary of the Invention [Problem to be solved by the invention]

[0004] The invention of Patent Document 1 can detect torque imbalance and rotation angle and correct the imbalance, but it cannot know what rotation speed is necessary to achieve sufficient machining accuracy when actually performing turning.

[0005] The present invention has as its technical object to solve the problems of the conventional technology, and to provide a machine tool that notifies an operator of the maximum command rotational speed or permissible rotational speed at which machining errors caused by vibrations due to unbalanced load do not exceed the permissible range. [Means for solving the problem]

[0006] According to the present invention, there is provided a machine tool which rotates a workpiece to perform turning, comprising a workpiece rotation device having a workpiece mounting portion for mounting a workpiece and a rotary motor for rotating the workpiece mounting portion, a control device which calculates an allowable rotational speed of the workpiece rotation device based on the amount of change in torque of the rotary motor when the workpiece rotation device with a workpiece mounted is rotated, and a display device which displays the allowable rotational speed of the workpiece rotation device calculated by the control device. Effect of the Invention

[0007] According to the present invention, when a workpiece is attached to the workpiece rotating device, an operator can know, prior to machining, the allowable rotation speed of the workpiece rotating device that keeps machining errors caused by vibrations due to unbalanced load within an allowable range. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic side view showing an example of a machine tool to which the present invention can be applied, showing a rotary table in a horizontal position. [Diagram 2] FIG. 1 is a schematic side view showing an example of a machine tool to which the present invention can be applied, illustrating a rotary table in a vertical position. [Diagram 3] 11A and 11B are diagrams for explaining a method for measuring an unbalanced load on a rotary table. [Figure 4] FIG. 13 is a diagram showing an example of a screen displaying the measurement result of the unbalanced load and the maximum command rotation speed displayed on the display device. [Diagram 5] FIG. 13 is a diagram showing an example of a screen displaying the measurement result of the unbalanced load and the maximum command rotation speed displayed on the display device. [Figure 6] FIG. 13 is a diagram showing an example of a screen displaying the measurement result of the unbalanced load and the maximum command rotation speed displayed on the display device. [Figure 7] FIG. 13 is a diagram showing an example of a screen displaying the measurement result of the unbalanced load and the maximum command rotation speed displayed on the display device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figures 1 and 2 are schematic side views of a machine tool as an example of a machine to which the present invention can be applied. Figure 1 shows a rotary table in a horizontal position, and Figure 2 shows the rotary table in a vertical position. In Figures 1 and 2, the machine tool 100 constitutes a horizontal machining center and is equipped with a bed 102 as a base fixed to the floor surface of a factory. On the top surface of the front part (left side in Figure 1) of the bed 102, a table 106 as a work rotation device that rotates an attached workpiece W is provided so as to be movable in the front-rear direction or the Z-axis direction (left-right direction in Figure 1).

[0010] A column 104 is provided on the upper surface of bed 102 at the rear end side (right side in FIG. 1) of bed 102 so as to be movable in the X-axis direction (a direction perpendicular to the paper surface in FIG. 1). A Y-axis slider 108 is attached to the front surface of column 104 so as to be movable in the vertical direction or the Y-axis direction. A spindle head 110 is attached to Y-axis slider 108. Spindle head 110 supports a spindle 112 so as to be rotatable about a horizontal rotation axis Os. Spindle head 110 has a spindle servo motor Ms that rotates and drives spindle 112.

[0011] The column 104 is guided in the X-axis direction by an inclined linear guide 130. The inclined linear guide 130 faces forward and upward as a whole, and is inclined so that the rear part is positioned higher than the front part. Specifically, the inclined linear guide 130 includes a front rail 134a and a rear rail 134b as X-axis guide rails, and a front block 132a and a rear block 132b that slide along the front rail 134a and the rear rail 134b are fixed to the lower surface of the column 104.

[0012] A ball screw (not shown) extending in the X-axis direction and an X-axis servo motor Mx connected to one end of the ball screw are attached to the bed 102 as an X-axis feed device that drives the column 104 to reciprocate along the X-axis guide rails 134a, 134b, and a nut (not shown) that engages with the ball screw is attached to the column 104. In addition, an X-axis scale (not shown) that detects the coordinate position of the column 104 in the X-axis direction is attached to the bed 102.

[0013] A pair of Y-axis guide rails (not shown) extending in the Y-axis direction are fixed to the front surface of the column 104, and the Y-axis slider 108 has a block that slides along the Y-axis guide rails. The column 104 is provided with a ball screw (not shown) extending in the Y-axis direction and a Y-axis servo motor My connected to one end of the ball screw as a Y-axis feed device that drives the Y-axis slider 108 back and forth along the Y-axis guide rails, and a nut (not shown) that engages with the ball screw is attached to the Y-axis slider 108. Also, a Y-axis scale (not shown) that detects the coordinate position of the Y-axis slider 108 in the Y-axis direction is attached to the column 104.

[0014] The table 106 is provided on the bed 102 in front of the column 104. The table 106 includes a first table base 114 and a second table base 116. The first table base 114 is provided on the bed 102 and moves on the bed 102 in the Z-axis direction. More specifically, a pair of left and right Z-axis guide rails 122 (only the right rail is shown in FIGS. 1 and 2) extending in the Z-axis direction are fixed to the upper surface of the bed 102, and a block (not shown) that slides along the Z-axis guide rails 122 is fixed to the first table base 114.

[0015] Bed 102 is provided with a ball screw (not shown) extending in the Z-axis direction and a Z-axis servo motor Mz connected to one end of the ball screw as a Z-axis feed device that drives first table base 114 back and forth along Z-axis guide rail 122, and a nut (not shown) that engages with the ball screw is attached to first table base 114. Bed 102 is provided with a Z-axis scale (not shown) that detects the coordinate position of first table base 114 in the Z-axis direction.

[0016] With regard to directions in machine tool 100 according to this embodiment, the rotation axis Os of spindle 112 extends horizontally, and the direction parallel to the rotation axis Os is defined as the Z-axis direction (also referred to as the front-rear direction). The direction in which spindle 112 protrudes along the Z-axis direction (leftward in Figs. 1 and 2) is the front, and the opposite direction (rightward in Figs. 1 and 2) is the rear. The horizontal direction perpendicular to the Z-axis direction (direction perpendicular to the paper surface of Figs. 1 and 2) is defined as the X-axis direction (also referred to as the left-right direction), and the vertical direction is defined as the Y-axis direction (also referred to as the up-down direction).

[0017] The first table base 114 has an inclined surface 114a that is inclined with respect to the moving direction of the table 106. Specifically, the inclined surface 114a is inclined at an angle θ=45° from the horizontal plane so as to face backward and upward.

[0018] The first table base 114 has an inclined rotary guide 118 along the inclined surface 114a. The inclined rotary guide 118 faces rearward and upward, with the front portion being positioned higher than the rear portion. The inclined rotary guide 118 rotates the second table base 116 around an inclined axis Oc perpendicular to the inclined surface 114a (i.e., perpendicular to the inclined rotary guide 118). The rotational feed direction of the second table base 116 is defined as the C-axis direction. The inclined rotary guide 118 can have, for example, a cross roller bearing.

[0019] The first table base 114 has a built-in C-axis servo motor Mc that rotates the second table base 116 around the tilt axis Oc. The first table base 114 is equipped with a C-axis detection device that detects the coordinate (rotational position) in the C-axis direction of the second table base 116. The C-axis detection device can be formed, for example, by a rotary encoder 124 attached to the C-axis servo motor Mc. As a driving device

[0020] The second table base 116 is provided on an inclined rotary guide 118. The second table base 116 has a swivel surface 116a. The swivel surface 116a is inclined at an angle of 45° with respect to the inclined surface 114a. The swivel surface 116a swivels around the inclination axis Oc as the second table base 116 rotates.

[0021] The second table base 116 has a rotary table 120 rotatably provided along the swivel plane 116a. The rotary table 120 is supported by the second table base 116 so as to be rotatable about a variable axis Ob perpendicular to the swivel plane 116a. It will be understood with reference to Figures 1 and 2 that the orientation of the variable axis Ob changes depending on the position of the second table base 116 in the C-axis direction. The rotational feed direction of the rotary table 120 around the variable axis Ob is defined as the B-axis direction.

[0022] The second table base 116 has a built-in B-axis servo motor Mb that rotates a rotary table 120, which serves as a workpiece mounting portion for mounting a workpiece W, about a variable axis Ob. The second table base 116 is equipped with a B-axis detection device that detects the coordinate (rotational position) of the rotary table 120 in the B-axis direction. The B-axis detection device can be formed, for example, by a rotary encoder 126 attached to the B-axis servo motor Mb.

[0023] The rotary table 120 has a workpiece mounting surface 120a on which a workpiece W is mounted. The workpiece W can be mounted on the workpiece mounting surface 120a via a pallet (not shown). The workpiece W may also be mounted directly on the workpiece mounting surface 120a. The workpiece mounting surface 120a is disposed in an arbitrary position depending on the position of the second table base 116 in the C-axis direction movable range. For example, in FIG. 1, the workpiece mounting surface 120a is in a horizontal position, and in FIG. 2, the workpiece mounting surface 120a is in a vertical position.

[0024] Machine tool 100 may be a machining center further equipped with a tool magazine (not shown) that stores a plurality of tools used in machining, an automatic tool changer (not shown) that changes tools between the tool magazine and spindle 112, and a coolant supplying device (not shown) that supplies coolant to the machining area of ​​machine tool 100, and these peripheral devices are housed in a cover (not shown) together with machine tool 100. Machine tool 100 may also include a setup station (not shown) where an operator attaches workpiece W to a pallet, a pallet exchanger (not shown) that exchanges pallets between the setup station and table 106, and the like.

[0025] The machine tool 100 further includes a control device 140 that controls the machine tool 100. The control device 140 can be composed of a computer and associated software including a CPU (Central Processing Unit), a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a storage device such as a HDD (Hard Disk Drive) or an SSD (Solid State Drive), an input / output port, and a bidirectional bus that interconnects these.

[0026] The control device 140 can be configured in software as part of a machine control device that controls an NC device that controls the spindle servo motor Ms, X-axis servo motor Mx, Y-axis servo motor My, Z-axis servo motor Mz, B-axis servo motor Mb and C-axis servo motor Mc, as well as related equipment of the machine tool, such as the tool magazine (not shown), automatic tool changer (not shown), pallet changer and coolant supply device of the above-mentioned machine tool, and further, an oil / air supply device (not shown) and a compressed air supply device (not shown).

[0027] Machine tool 100 further includes a display device 142. As an example, display device 142 can be formed of a touch panel (not shown) attached to an operation panel (not shown) attached to the above-mentioned cover surrounding machine tool 100. When display device 142 is formed of a touch panel, display device 142 also forms an input device with which an operator inputs numerical values ​​to control device 140 and selects an operation mode.

[0028] The control device 140 outputs a current command value to the servo amplifier 144 in accordance with the NC program read and interpreted by the NC device. The servo amplifier 144 supplies current to each of the spindle servo motor Ms, the X-axis servo motor Mx, the Y-axis servo motor My, the Z-axis servo motor Mz, the B-axis servo motor Mb, and the C-axis servo motor Mc in accordance with the current command value from the control device 140. In this way, the machine tool 100 machines the workpiece W in accordance with the NC program.

[0029] The operation of this embodiment will now be described. Machine tool 100 can perform milling of workpiece W attached to rotary table 120 by attaching a rotating tool (not shown) to the tip of spindle 112, and relatively moving table 106 and spindle 112 in three orthogonal axial directions of X, Y, and Z and in the rotational directions of B and C axes while rotating spindle 112. Machine tool 100 can also perform turning by attaching a cutting tool 128 to the tip of spindle 112, and rotating table 120 while moving table 106 and spindle 112 in three orthogonal axial directions of X, Y, and Z when rotary table 120 is in a horizontal position.

[0030] When turning the workpiece W, the rotary table 120 must be rotated at a higher speed than when milling with a rotary tool. The rotation speed of the rotary table 120 during turning can be, for example, 100 to 800 rpm. A relatively heavy workpiece W may be attached to the rotary table 120, and the workpiece W may have various shapes, particularly an asymmetric shape. Therefore, an unbalanced load acts on the bearing that supports the rotary table 120 to rotate on the second table base 116, and the rotary table 120 may vibrate when rotated. When the rotary table 120 vibrates, not only does the machining accuracy of the turning process decrease, but in some cases, the tool or machine may be damaged, making it impossible to perform the process.

[0031] Therefore, in the present invention, as described below, a workpiece W is attached to the rotating table 120 before machining, the workpiece mounting surface 120a is positioned in a vertical or inclined position, and the amount of change in torque of the B-axis servo motor Mb when the rotating table 120 is rotated is calculated, and the allowable rotational speed of the rotating table 120 is calculated based on the amount of change in torque.

[0032] 3 shows the change in torque of the B-axis servo motor Mb when the rotary table 120 is rotated. The torque of the B-axis servo motor Mb can be detected by detecting the current value output from the servo amplifier 144 to the B-axis servo motor Mb. The rotational position of the rotary table 120 in the B-axis direction or the rotational position of the B-axis servo motor Mb can be detected by the rotary encoder 124 provided on the B-axis servo motor Mb. In this way, the change in torque of the B-axis servo motor Mb can be obtained based on the current value supplied to the B-axis servo motor Mb and the rotational position of the B-axis servo motor Mb at that time.

[0033] FIG. 3 shows an example of the change in torque of the B-axis servo motor Mb. The torque of the B-axis servo motor Mb has a positive value when rotated forward and a negative value when rotated reversely. When the workpiece mounting surface 120a is positioned in a vertical or inclined position and rotated, the torque of the B-axis servo motor Mb changes in one period for one rotation of the rotary table due to an unbalanced load. In FIG. 3, the change in torque of the B-axis servo motor Mb is approximated by a sine wave curve. The vertical axis of the graph in FIG. 3 is the torque (kgm) of the B-axis servo motor, and in this embodiment, the torque is measured by rotating the B-axis servo motor in the reverse direction, so it is a negative value.

[0034] In FIG. 3, curve SC1 represents an example of the change in torque of the B-axis servo motor Mb when the workpiece W is not attached to the rotary table 120. Curve SC2 represents an example of the change in torque of the B-axis servo motor Mb when the workpiece W is attached to the rotary table 120. Curves SC1 and SC2 are obtained by fitting a model function T=αsin(θ-δ)+Ta using a curve fitting method such as the least squares method, where T is the measured torque value of the B-axis servo motor Mb and θ is the angular position relative to the origin of the B-axis around the tilt axis Ob. Here, α is the amplitude of the torque, δ is the phase shift relative to the origin of the B-axis, and Ta is the average value of the change in torque of the B-axis servo motor Mb. In the example of FIG. 3, when the workpiece W is attached to the rotary table 120 and rotated, the deviation from Ta on curve SC2 representing the change in torque of the B-axis servo motor Mb is maximum (Dmax) at the position where the angular position relative to the origin of the B-axis is θ=120°.

[0035] The unbalanced load is automatically measured by executing an unbalanced load measurement program in the control device 140. When the unbalanced load measurement program is executed, a measurement screen 200 as shown in Fig. 4 is displayed on the display device 142. The measurement screen 200 includes a first machining condition display area 202 that displays precision machining conditions, a second machining condition display area 204 that displays rough machining conditions, an unbalance display area 206 that displays the magnitude (kgm) and direction (deg) of the unbalanced load torque, a counterweight display area 208 that displays the position and mass of the counterweight, a graphic area 210 that visually displays the position of the unbalanced load and the counterweight mounting position, and a start button 212.

[0036] After confirming that the workpiece W is attached to the rotating table 120, the operator taps the start button 212, and the control device 140 moves the first table base 114 to a predetermined Z position (measurement position) and rotates the second table base 116 in the C-axis direction around the tilt axis Oc. When the rotating table 120 moves to the vertical position shown in Fig. 2, the control device 140 stops the rotation of the rotating table 120. As a result, the workpiece W attached to the rotating table 120 is set in a direction that will fall due to gravity.

[0037] When the turntable 120 reaches the vertical position, which is the gravity drop position, the control device 140 then rotates the turntable 120 at a predetermined measurement rotation speed, for example 10 rpm, while reading the position of the turntable 120 in the B-axis direction, i.e., the rotational position of the turntable 120 around the variable axis Ob, from a signal from the rotary encoder 126 of the B-axis servo motor Mb, and accesses the servo amplifier 144 to read the current value supplied to the B-axis servo motor Mb from the servo amplifier 144. By matching these two values, the angular position θmax around the variable axis Ob that gives the maximum offset load Dmax is calculated.

[0038] When the measurement is completed, the unbalanced load value α and the angular position θmax determined by calculation are displayed in the unbalance display area 206 (see FIG. 5). In FIG. 5 shown as an example, the unbalanced load value α=3.5 kgm and the angular position θmax (unbalance direction)=235° are displayed in the unbalance display area 206.

[0039] Moreover, the control device 140 calculates the maximum command rotational speed or allowable rotational speed as the precision machining condition, and the maximum command rotational speed or allowable rotational speed as the rough machining condition. As shown below, the control device 140 stores in advance a machine-specific threshold value A(i) based on the actual measurement value of the vibration amplitude allowable as the precision machining condition in association with a plurality of rotational speeds, and determines the maximum command rotational speed based on the above calculation result so that the value of α×A does not exceed A(i). Here, α is the amplitude of the B-axis motor torque, and A is a machine-specific coefficient that indicates the ease of vibration obtained based on the machine stiffness. 800rpm:A(9) 700rpm:A(8) 600rpm:A(7) 500rpm:A(6) 400rpm:A(5) 300rpm:A(4) 200rpm:A(3) 100rpm:A(2) 0rpm:A(1)

[0040] Similarly, the control device 140 pre-stores machine-specific threshold values ​​B(i) based on actual measured values ​​of vibration amplitudes acceptable as rough machining conditions, in association with multiple rotational speeds, and determines the maximum command rotational speed based on the above calculation results so that the value of α×A does not exceed B(i). 800rpm:B(9) 700rpm:B(8) 600rpm:B(7) 500rpm:B(6) 400rpm:B(5) 300rpm:B(4) 200rpm:B(3) 100rpm:B(2) 0rpm:B(1)

[0041] In the above example, the control device 140 shows A(i) and B(i) at 0 rpm, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, and 800 rpm, but the above multiple rotational speeds may be selected to have more or fewer rotational speeds. Alternatively, the value of A(i) or B(i) for a rotational speed between the above multiple rotational speeds, for example, 750 rpm between 700 rpm and 800 rpm as shown in FIG. 6, may be interpolated from A(i) or B(i) for 700 rpm and 800 rpm. As an example, in FIG. 5, a maximum command rotational speed of 500 rpm as a precision machining condition is displayed in the first machining condition display area 202, and a maximum command rotational speed of 750 rpm as a rough machining condition is displayed in the second machining condition display area 204.

[0042] At the same time, the control device 140 displays 55° in the counterweight display area 208 as the direction for attaching the counterweight, and displays an icon 214 indicating the direction of imbalance and an icon 216 indicating the direction for attaching the counterweight in the graphic area 210. The direction for attaching the counterweight is the diagonal direction φ of the angular position θmax that gives the maximum unbalanced load Dmax, and is calculated as φ=θmax+180°.

[0043] Since the workpiece W is attached to the rotating table 120, the position where the counterweight is attached cannot be freely determined. Therefore, the counterweight display area 208 and the graphic area 210 show the direction in which the counterweight is attached. Based on the measurement result of the unbalanced load, the operator appropriately selects a position on the workpiece attachment surface 120a of the rotating table 120 where the counterweight can be attached along the φ direction, and inputs the distance r from the rotation center of the rotating table 120 of that position into the input dialog box 218 in the counterweight display area 208 (see FIG. 6). This input operation can be performed, for example, from a keyboard arranged on the operation panel. Alternatively, when the operator taps the input dialog box 218 on the touch panel constituting the display device 142, a numeric keypad (not shown) may be displayed on the touch panel, and the operator may tap the numeric keypad to input.

[0044] As an example, Fig. 6 shows that the operator has input 200 mm into the input dialog box 218. If the mass of the counterweight is M, then the mass M of the counterweight can be calculated from M = α / r. In Fig. 6, as a result of the operator inputting 200 mm (r = 0.2 m), the control device 140 displays 17.5 kg in the counterweight display area 208 as the mass M of the counterweight to be attached to the rotating table 120 based on M = α / r.

[0045] At this time, if the desired rotation speed of the rotary table 120 is lower than the maximum command rotation speed displayed in the first machining condition display area 202 or the maximum command rotation speed displayed in the second machining condition display area 204, the desired rotation speed can be input to the control device 140 to perform precision turning or rough turning. The precision turning or rough turning is performed according to the machining program. If the desired rotation speed of the rotary table 120 is higher than the maximum command rotation speed, the operator can attach a counterweight to the rotary table 120 and perform the process of measuring the unbalanced load and the process of calculating the maximum command rotation speed again.

[0046] When the operator attaches a counterweight with a mass M of 17.5 kg to the position of φ=55° and r=0.2 m on the workpiece mounting surface 120a of the rotary table 120 and taps the start button 212, the control device 140 executes the above-mentioned unbalanced load measurement process again according to the unbalanced load measurement program. Referring to FIG. 7, the unbalanced load measurement result with the counterweight attached is shown. In FIG. 7 shown as an example, the unbalanced load value α=0.2 kgm and the angular position θmax (unbalanced direction)=235° are displayed in the unbalance display area 206, the maximum command rotation speed of 800 rpm as the precision machining condition is displayed in the first machining condition display area 202, and the maximum command rotation speed of 800 rpm as the rough machining condition is displayed in the second machining condition display area 204.

[0047] When the desired rotation speed of the rotary table 120 is lower than the maximum command rotation speed displayed in the first machining condition display area 202 or the maximum command rotation speed displayed in the second machining condition display area 204, the operator inputs the desired rotation speed into the control device 140 to perform precision turning or rough turning. The precision turning or rough turning is performed according to the machining program.

[0048] According to this embodiment, when the workpiece W is attached to the rotary table 120, the operator can know the direction in which the unbalanced load will occur and the magnitude of the unbalanced load torque, the maximum command rotational speed under the precision machining conditions and the rough machining conditions, and the direction in which the counterweight should be attached and the mass, and further, the direction in which the unbalanced load will occur and the magnitude of the unbalanced load torque when the counterweight is actually attached, the maximum command rotational speed under the precision machining conditions and the rough machining conditions, and the direction in which the counterweight should be attached and the mass. By knowing the maximum command rotational speed under the precision machining conditions and the rough machining conditions, the operator can easily determine whether to continue machining as is or to correct the unbalanced load.

[0049] In the above embodiment, the unbalanced load is measured with the rotary table 120 placed in the vertical position where the effect of the unbalanced load is greatest, but the position of the rotary table 120 during the unbalanced load measurement is not limited to this. The machine tool 100 can also perform turning by placing the rotary table 120 at any tilt position between the horizontal position and the vertical position and rotating the rotary table 120. Therefore, the unbalanced load measurement process and the calculation of the maximum command rotation speed may be executed with the second table stand 116 rotated and the rotary table 120 placed at a desired tilt position. In other words, the unbalanced load measurement process and the calculation of the maximum command rotation speed can be executed by positioning the rotary table 120 at the tilt angle when actually performing turning.

[0050] Furthermore, if the rotation speed of the rotary table 120 input by the operator to the control device 140 is higher than the maximum command rotation speed, an alarm may be sounded or a warning light (not shown) may be turned on. [Explanation of symbols]

[0051] 100 Machine tools 102 Beds 104 Column 106 Table 108 Y-axis slider 110 Spindle head 112 Main axis 114 First Table Base 114a Slope 116 Second Table Base 116a Turning surface 120 Rotating Table 120a Work mounting surface 122 Z-axis guide rail 124 Rotary Encoder 126 Rotary Encoder 128 bytes 132a Front block 132b Rear block 134a X-axis guide rail 134b X-axis guide rail 140 Control device 142 Display device 144 Servo Amplifier 200 Measurement screen 202 First processing condition display area 204 Second processing condition display area 206 Unbalanced display area 208 Counterweight display area 210 Graphics Area 212 Start button 214 Icons 216 Input Dialog Box Mb B-axis servo motor Mc C-axis servo motor Ms spindle servo motor Mx X-axis servo motor My Y-axis servo motor Mz Z-axis servo motor

Claims

1. In machine tools that rotate the workpiece to perform turning, A work rotation device having a work mounting portion for mounting a work and a rotation motor for rotating the work mounting portion; a control device that calculates an allowable rotation speed of the work rotation device based on a change in torque of the rotation motor when the work rotation device with a work attached thereto is rotated; A display device that displays the allowable rotation speed of the workpiece rotating device calculated by the control device; and A machine tool comprising:

2. 2. The machine tool according to claim 1, wherein the control device calculates an allowable rotational speed for precision machining and an allowable rotational speed for rough machining, and displays the allowable rotational speed for precision machining and the allowable rotational speed for rough machining on a display device.

3. 2. The machine tool according to claim 1, wherein the work mounting portion includes a rotating table having a work mounting surface for mounting the work, the rotating table being capable of being positioned in a plurality of postures between a horizontal position where the work mounting surface is horizontal and a vertical position where the work mounting surface is vertical, and the rotating table is positioned in an inclined position or a vertical position to measure changes in the torque of the rotary motor.

4. 4. A machine tool according to claim 3, wherein said rotary table is positioned at an inclination angle between said horizontal position and said vertical position when actually performing turning, and a change in torque of said rotary motor is measured.

5. 2. The machine tool according to claim 1, wherein the workpiece rotating device comprises a first table base attached to a bed of the machine tool and a second table base attached to the first table base, the workpiece mounting portion comprises a rotating table having a workpiece mounting surface for mounting the workpiece, the rotating table is rotatably mounted to the second table base, and the second table base is supported by the first table base so as to be rotatable about an inclination axis.

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