Machine tool

Abstract

To surely detect abnormality of a mounting state of a tool to a main spindle.SOLUTION: The machine tool includes a spindle 2 configured to rotate about a rotation axis O1, feed means 11, 12, 13 configured to position the spindle 2 in an X-direction, a Y-direction, and a Z-direction with respect to a workpiece W, a current detection unit 17 configured to detect current values of motors 14 of the feed means 11, 12, 13 as idling loads, and an abnormality determination unit 26 configured to determine presence or absence of an abnormality based on the current values (idling loads) detected by the current detection unit 17.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a machine tool. [Background technology]

[0002] In recent years, machining has become mainstream in machining centers equipped with automatic tool changers. Machining centers can automatically change tools attached to their spindles, but the tradeoff is that when changing tools, foreign matter (chips) can become caught in the attachment area between the spindle and the tool. If foreign matter becomes caught between the spindle and the tool, misaligning the spindle's rotation axis and the tool's axis can cause the tip of the tool to wobble during machining, resulting in problems such as an increased hole diameter in the workpiece. Therefore, in order to guarantee the machining quality of the workpieces, the current practice is to measure the dimensions of the machined parts of all workpieces during a post-machining inspection process, which requires particularly strict machining precision.

[0003] However, automatically measuring the dimensions of the processed part of the workpiece using a measuring device increases equipment costs, while manually measuring the dimensions of the processed part of the workpiece requires more man-hours, resulting in increased production costs.

[0004] For example, Patent Document 1 listed below discloses a method for detecting whether or not a foreign object is caught between a tool and a spindle. This method determines whether or not a foreign object is caught between the tool and the spindle by comparing the power consumption of the drive unit when the tool is driven to rotate with the reference power consumption when no foreign object is caught between the tool and the spindle. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-283461 Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the difference between the reference power consumption when no foreign object is caught between the tool and the spindle and the power consumption when a foreign object is caught between the tool and the spindle is extremely small, it cannot be said that the above method can reliably detect the presence of a foreign object.

[0007] Therefore, an object of the present invention is to reliably detect an abnormality in the attachment state of a tool to a spindle. [Means for solving the problem]

[0008] (1) The machine tool according to the present invention, which was invented to solve the above problems, comprises a spindle to which a tool for machining a workpiece is attached and which rotates around a rotation axis; a positioning means for positioning the spindle relative to the workpiece in a direction perpendicular to the rotation axis; a load detection means for detecting the idling load applied to the positioning means by causing the tool to rotate freely by the spindle without contacting the workpiece; and an abnormality determination means for determining whether or not there is an abnormality in the attachment state of the tool to the spindle based on the idling load detected by the load detection means.

[0009] When the tool is properly attached to the spindle, the tool's axis (center of gravity) coincides with the spindle's rotation axis. In this state, even if the tool is rotated idly without contact with the workpiece, the tool will not substantially vibrate due to centrifugal force. As a result, the tool's positional deviation is small, and the load applied to the positioning device during idling is small. On the other hand, if the tool is attached abnormally to the spindle, for example, due to a foreign object getting caught between the tool and the spindle, the tool's axis (center of gravity) will be misaligned with the spindle's rotation axis. In this state, if the tool is rotated idly without contact with the workpiece, the tool's runout due to centrifugal force will be very large. As a result, the tool's positional deviation will be large, and the load applied to the positioning device during idling will be large. Thus, the load during idling varies significantly depending on whether the tool is attached to the spindle abnormally. Therefore, by making a determination based on the load during idling as in the above configuration, it is possible to reliably detect an abnormality in the tool's attachment to the spindle.

[0010] (2) In the configuration of (1) above, the rotational speed of the main shaft when detecting the idling load may be the maximum rotational speed of the main shaft.

[0011] In this way, the tool rotates freely at high speed when detecting the idling load. Therefore, if the tool is attached to the spindle abnormally, the tool vibration caused by centrifugal force becomes very large. As a result, the difference in the idling load becomes significant depending on whether or not the tool is attached to the spindle abnormally. Therefore, it is possible to more reliably detect an abnormality in the tool attachment to the spindle.

[0012] (3) In the configuration of (1) or (2) above, the rotation speed of the spindle when detecting the idling load may be greater than the rotation speed of the spindle when machining the workpiece.

[0013] In this way, the tool rotates freely at high speed when detecting the idling load. Therefore, if the tool is attached to the spindle abnormally, the tool vibration caused by centrifugal force becomes very large. As a result, the difference in the idling load becomes significant depending on whether or not the tool is attached to the spindle abnormally. Therefore, it is possible to more reliably detect an abnormality in the tool attachment to the spindle.

[0014] (4) In any of the configurations (1) to (3) above, it is preferable that the positioning means is a servo motor incorporating a current detection unit that detects the value of a current flowing inside and a control unit that controls the output based on the detected current value, and that the load detection means is the current detection unit.

[0015] By using the current detector of the servo motor as the load detector in this way, it is not necessary to provide a separate load detector, which allows for cost reduction. [Effects of the Invention]

[0016] According to the present invention, an abnormality in the attachment state of a tool to a spindle can be reliably detected. [Brief explanation of the drawings]

[0017] [Figure 1]1 is a perspective view showing a machine tool according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram of a feeding means of the machine tool. [Figure 3] FIG. 1 is a schematic side view of a spindle and a tool that are properly attached. [Figure 4] FIG. 10 is a schematic side view of a spindle and a tool mounted with a foreign object caught therein. [Figure 5] 10 is a graph showing an example of a change in the current value of a motor of an X-direction feed means. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] A machine tool according to one embodiment of the present invention automatically performs cutting operations such as milling, drilling, and boring on a workpiece W. As shown in FIG. 1 , the machine tool includes a spindle 2 to which a tool 1 is attached, a spindle motor 3 that rotates the spindle 2 about a rotation axis O1, a workpiece setting unit 4 on which the workpiece W is set, and a housing (not shown) that accommodates these components. The machine tool of this embodiment is a so-called machining center that includes an automatic tool changer 5 that automatically replaces the tool 1 attached to the spindle 2 with another tool. The tool 1 may be one with multiple cutting edges arranged at equal intervals around the circumferential direction, or one with a cutting edge arranged at a single location around the circumferential direction. In this embodiment, the direction parallel to the rotation axis O1 of the spindle 2 is referred to as the Z direction, and two directions that are perpendicular to the Z direction and perpendicular to each other are referred to as the X direction and the Y direction, respectively.

[0020] The machine tool has positioning means for positioning the spindle 2 in the X, Y, and Z directions relative to the workpiece W set in the workpiece setting unit 4. In the illustrated example, the positioning means in the X, Y, and Z directions include an X-direction feed means 11, a Y-direction feed means 12, and a Z-direction feed means 13 for linearly reciprocating the spindle 2 in each direction.

[0021] As shown in FIG. 2 , each of the feed means 11, 12, and 13 includes a motor 14 and a motion conversion mechanism 15 (e.g., a rack-and-pinion mechanism) that converts the rotational motion of the motor 14 into linear motion. The motor 14 may be, for example, a servo motor whose position, rotation speed, torque, and other parameters can be controlled as instructed. Specifically, the motor 14 incorporates a detector that detects its own state and a controller 16 that controls the output (current) of the motor 14 based on the value detected by the detector. The detector may include, for example, a current detector 17 that detects the value of the current flowing inside the motor 14. In this embodiment, the motor 14 may further include a voltage detector 18 that detects the voltage inside the motor 14 and a rotation speed detector 19 that detects the rotation speed (rotation phase) of the motor 14. Alternatively, a general-purpose motor without a built-in detector and controller may be used as the motor 14, with the detector and controller being provided externally to the motor 14.

[0022] In this embodiment, the workpiece setting unit 4 is fixed to the housing, and the spindle 2 is movable in the X, Y, and Z directions relative to the housing. The tool 1 can be placed at any three-dimensional position by positioning the spindle 2, to which the tool 1 is attached, in the X, Y, and Z directions using feed means 11, 12, and 13. Alternatively, the spindle 2 may be fixed to the housing, while the workpiece setting unit 4 is movable relative to the housing in one or more of the X, Y, and Z directions.

[0023] The spindle motor 3, the automatic tool changer 5, the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13 are connected to a control device 20 (see FIG. 1). The control device 20 is, for example, a computer, and has an input unit 21, an output unit 22, a memory unit 23, a calculation unit 24, a command unit 25, and an abnormality determination means 26. The calculation unit 24 performs calculations based on information input from the input unit 21 and information stored in the memory unit 23, and the command unit 25 issues commands based on the results of the calculations to the spindle motor 3, the feed means 11, 12, 13, and the automatic tool changer 5 via the output unit 22, thereby automatically performing machining with the tool 1 and changing the tool 1.

[0024] For example, if the tool 1 deviates from its predetermined position in the X direction before or during machining, the value detected by the detector of the motor 14 of the X-direction feed means 11 (for example, the number of rotations detected by the rotation number detector 19) will deviate from a predetermined value that has been set in advance. When this signal is transmitted to the control unit 16 of the motor 14, the control unit 16 calculates the current value required to return the tool 1 to the predetermined position and supplies this current value to the motor 14 of the X-direction feed means 11. By performing the above-mentioned feedback control, the tool 1 can always be placed in the predetermined position. The same positioning control as above is also performed by the Y-direction feed means 12 and the Z-direction feed means 13.

[0025] For example, when the tool 1 is normally attached to the spindle 2, i.e., when the axis (center of gravity) O2 of the tool 1 and the rotation axis O1 of the spindle 2 are aligned, and the tool 1, which is not in contact with the workpiece W, is idly rotated by the spindle 2, as shown in FIG. 3, the tool 1 does not substantially vibrate due to centrifugal force. Therefore, the tool 1 does not substantially apply a load that tends to move the tool 1 in the X, Y, or Z directions due to the vibrating tool 1. In this case, the tool 1 is positioned at a predetermined position in the X, Y, and Z directions, so there is no need to correct the position of the tool 1 using the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13. Therefore, the current values ​​(output values ​​of the control unit 16) of the motors 14 of the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13 are relatively small. Furthermore, even when the Z-direction feed means 13 moves the spindle 2 in the Z direction at a predetermined speed while the tool 1 is rotating idly, if the tool 1 is attached to the spindle 2 in a normal state, the current value of the motor 14 of the Z-direction feed means 13 will be relatively small.

[0026] On the other hand, if the tool 1 is attached to the spindle 2 in an abnormal state, i.e., if the axis of the tool does not coincide with the rotation axis of the spindle 2, and the tool 1, which is not in contact with the workpiece W, is rotated by the spindle 2, the runout (vibration) of the tool 1 due to centrifugal force will be large, as shown in FIG. 4. As a result, a load will be generated that tries to move the tool 1 in any of the X, Y, and Z directions. In this case, the tool 1 will deviate from its predetermined position in any of the X, Y, and Z directions, so that current is supplied to the motor 14 of the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13 to return the tool 1 to its predetermined position. Therefore, the current value (output value of the control unit 16) of at least one of the motors 14 of the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13 will be relatively large. Furthermore, even when the Z-direction feed means 13 is used to move the spindle 2 in the Z direction at a predetermined speed while the tool 1 is rotating idly, if the tool 1 is attached to the spindle 2 in an abnormal state, the current value of the motor 14 of the Z-direction feed means 13 may become relatively large.

[0027] Therefore, in this embodiment, before machining, while the tool 1, which does not contact the workpiece W, is idling by the spindle 2, at least one of the current value of the motor 14 of the X-direction feed means 11, the current value of the motor 14 of the Y-direction feed means 12, and the current value of the motor 14 of the Z-direction feed means 13 is detected continuously or at predetermined intervals (e.g., every 1 / 1000 seconds) by a current detection unit 17 serving as a load detection means, and the detected current value is transmitted to the control device 20 as the idling load. Based on the current value of the motor 14 (idling load) transmitted to the control device 20 in this manner, an abnormality determination means 26 determines whether or not there is an abnormality in the attachment state of the tool 1 and the spindle 2. Note that depending on the type of machine tool, when the attachment state of the tool 1 to the spindle 2 is abnormal, the tendency of the change in the current value may vary, such as the current value of the motor 14 of the X-direction feed means 11, the current value of the motor 14 of the Y-direction feed means 12, or the current value of the motor 14 of the Z-direction feed means 13 changing significantly. Therefore, from the viewpoint of suppressing variations in detection accuracy among machine tools, it is preferable to detect the current value (idle load) of the motor 14 of the X-direction feed means 11, the current value (idle load) of the motor 14 of the Y-direction feed means 12, and the current value (idle load) of the motor 14 of the Z-direction feed means 13, and determine whether or not there is an abnormality in the attachment state between the tool 1 and the spindle 2 based on all of these current values. Of course, for example, if there is an abnormality in the attachment state of the tool 1 to the spindle 2 and the current value of the motor 14 of the X-direction feed means 11 and / or the current value of the motor 14 of the Y-direction feed means 12 is likely to change, then it is also possible to determine whether or not there is an abnormality in the attachment state between the tool 1 and the spindle 2 based on the current value (idle load) of the motor 14 of the X-direction feed means 11 and the current value (idle load) of the motor 14 of the Y-direction feed means 12.

[0028] The rotation speed of the spindle 2 when detecting the idling load is preferably, for example, 80% or more of the maximum rotation speed of the spindle 2 (the maximum rotation speed determined by the machine tool specifications), and more preferably the maximum rotation speed of the spindle 2. Alternatively, the rotation speed of the spindle 2 when detecting the idling load is preferably greater than the rotation speed of the spindle 2 when machining the workpiece W. Specifically, the rotation speed of the spindle 2 when detecting the idling load is preferably, for example, 8000 rpm or more. In this way, the tool 1 is idling at high speed by the spindle 2, and the difference in the current values ​​(idling loads) of the motors 14 of the feed means 11, 12, and 13 is likely to increase depending on whether there is an abnormality in the attachment state of the tool to the spindle. In other words, the abnormality determination means 26 can easily determine whether there is an abnormality in the attachment state of the tool 1 and the spindle 2.

[0029] In this embodiment, when detecting the idling load, the tool 1, which is not in contact with the workpiece W, is idled while the spindle 2 is moved along the rotation axis O1 so that the tool 1 approaches the workpiece W, i.e., while the spindle 2 is moved in the Z direction (e.g., downward) by the Z direction means 13. In this manner, if it is determined that the attachment state of the tool 1 and the spindle 2 is normal, the tool 1, which is moving along the rotation axis O1 together with the spindle 2, can be brought into contact with the workpiece W as is. Therefore, after determining whether or not there is an abnormality in the attachment state of the tool 1 relative to the spindle 2, machining of the workpiece W can be smoothly started. Note that when detecting the idling load, the tool 1, which is not in contact with the workpiece W, may be idled without moving the spindle 2 along the rotation axis O1.

[0030] FIG. 5 shows the change in the current value (black area indicated by "No Abnormality") of the motor 14 of the X-direction feed means 11 when the tool 1 is idled without contacting the workpiece W with the axis O2 of the tool 1 and the rotation axis O1 of the spindle 2 aligned, and the current value (gray area indicated by "Abnormality") detected by the current detection unit 17 of the motor 14 of the X-direction feed means 11 when the tool 1 is idled with the axis O2 of the tool 1 and the rotation axis O1 of the spindle 2 not aligned. In the figure, the vertical axis represents the current value detected by the current detection unit 17 of the motor 14 of the X-direction feed means 11, and the horizontal axis represents the Z-axis coordinate of the tool 1 (the right side of the figure represents the direction of approach to the workpiece W). Each current value in the figure is the value detected when the spindle 2 is moved at a constant speed in the Z direction by the Z-direction means 13 so that the tool 1 approaches the workpiece W. Period T1 in the figure is the period before machining when the tool 1 is rotating without contacting the workpiece W, and period T2 in the figure is the period during machining when the tool 1 is rotating while in contact with the workpiece W. The set rotation speed of the spindle 2 is the same in periods T1 and T2. Noise components contained in the current waveform in the figure have been removed in advance.

[0031] As can be seen from Figure 5, the current value (in the illustrated example, the magnitude of the amplitude) of the motor 14 of the X-direction feed means 11 when the tool 1 is idling (period T1) differs greatly between when there is an abnormality in the attachment state between the tool 1 and the spindle 2 and when there is. A similar tendency may also appear in the current value of the motor 14 of the Y-direction feed means 12 and the current value of the motor 14 of the Z-direction feed means 13. Therefore, it is possible to determine whether there is an abnormality in the attachment state between the tool 1 and the spindle 2 based on the current value of at least one of the motor 14 of the X-direction feed means 11, the motor 14 of the Y-direction feed means 12, and the motor 14 of the Z-direction feed means 13.

[0032] For example, by setting a threshold value for the current value of the motor 14 of the X-direction feed means 11, it is possible to determine whether or not there is an abnormality in the attachment state of the tool 1 and the spindle 2. Specifically, when the zero value of the current value of the motor 14 during a period T1 in which the tool 1 is idling before machining is defined as A, and the absolute value of the difference between the measured current value at each time (each Z-axis coordinate) and the zero value A is defined as the amplitude, a threshold value B for the amplitude is set. If the amplitude of the current value of the motor 14 exceeds threshold B, the abnormality determination means 26 determines that there is an abnormality in the attachment state of the tool 1 and the spindle 2. For example, in the example shown in FIG. 5, during period T1 in which the tool 1 is idling before machining, the amplitude of the current value in the black portion is always below threshold B, and therefore is determined to be "no abnormality," while the amplitude of the current value in the gray portion exceeds threshold B, and therefore is determined to be "abnormal."

[0033] When the difference between the amplitude of the current value of the motor 14 when the attachment state of the tool 1 and the spindle 2 is normal and the amplitude of the current value of the motor 14 when the attachment state of the tool 1 and the spindle 2 is abnormal is small, the presence or absence of an abnormality in the attachment state of the tool 1 and the spindle 2 may be determined based on the integrated value of the current value of the motor 14 during the period T1 when the tool 1 is idling before machining. Alternatively, the presence or absence of an abnormality in the attachment state of the tool 1 and the spindle 2 may be determined based on the value of the power (for example, the square) of the amplitude of the current value of the motor 14 during the period T1 when the tool 1 is idling before machining. This makes the effect of a large amplitude more apparent, improving the reliability of the determination.

[0034] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but redundant description of points similar to those of the above-described embodiment will be omitted.

[0035] For example, the voltage detection unit 18 of at least one of the motors 14 of the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13 may function as the load detection unit, and the abnormality determination unit 26 may determine whether or not there is an abnormality in the attachment state between the tool 1 and the spindle 2 based on the voltage of the motor 14 detected by the voltage detection unit 18. Alternatively, the rotation speed detection unit 19 of at least one of the motors 14 of the X-direction feed means 11, the Y-direction feed means 12, and the Z-direction feed means 13 may function as the load detection unit, and the abnormality determination unit 26 may determine whether or not there is an abnormality in the attachment state between the tool 1 and the spindle 2 based on the rotation speed of the motor 14 detected by the rotation speed detection unit 19.

[0036] In the above embodiment, the load detection means has been described as having a function to detect the load during idling while the tool 1 is rotating without contacting the workpiece W, and a function to detect the load during machining while the tool 1 is rotating while in contact with the workpiece W, but the load detection means for detecting the load during idling and the load detection means for detecting the load during machining may be provided separately. However, from the viewpoint of making the machine tool more compact and reducing costs, it is preferable that one load detection means has a function to detect the load during idling and a function to detect the load during machining.

[0037] The present invention is not limited to machining centers, but can also be applied to machine tools that do not have an automatic tool changer. [Explanation of symbols]

[0038] 1 tool 2 main shaft 3 spindle motor 4 Work Set Section 5 Automatic tool changer 11 X-direction feed means (positioning means) 12 Y-direction feed means (positioning means) 13 Z-direction feed means (positioning means) 14 Motor 15 Motion conversion mechanism 16 Control Unit 17 Current detection unit (load detection means) 18 Voltage detection section 19 Rotation speed detector 20 Control device 26 Abnormality determination means O1 Spindle rotation axis O2 Tool axis double work

Claims

1. a spindle to which a tool for machining a workpiece is attached and which rotates around a rotation axis; a positioning means for positioning the spindle relative to the workpiece in a direction perpendicular to the rotation axis; a load detection means for detecting a load applied to the positioning means during idle rotation by causing the tool to idle with the spindle in a state of non-contact with the workpiece; an abnormality determination means for determining whether or not there is an abnormality in the attachment state of the tool to the spindle based on the idling load detected by the load detection means.

2. 2. The machine tool according to claim 1, wherein the rotational speed of the spindle when detecting the idling load is the maximum rotational speed of the spindle.

3. 3. The machine tool according to claim 1, wherein the rotation speed of the spindle when the idling load is detected is greater than the rotation speed of the spindle when the workpiece is machined.

4. the positioning means is a servo motor incorporating a current detection unit that detects a current value flowing inside and a control unit that controls an output based on the detected current value, 3. The machine tool according to claim 1, wherein the load detecting means is the current detecting section.

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