Machine tools

Abstract

To surely detect abnormality of a mounting state of a tool to a spindle by a low-cost method.SOLUTION: A machine tool includes: a spindle 2 that is attached with a tool 1 and rotates about a rotation axis O1; feeding means 11 and 12 for positioning the spindle 2 in an X direction and a Y direction with respect to a work W; a current detection unit 17 for detecting a current value of a motor 14 of the feeding means 11 and 12; and abnormality determination means 26 for determining presence or absence of abnormality based on the current value detected by the current detection unit 17.SELECTED DRAWING: Figure 3

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] SUMMARY OF THE INVENTION It is therefore an object of the present invention to reliably detect an abnormality in the attachment state of a tool to a spindle using a low-cost method. [Means for solving the problem]

[0008] FIG. 4 is a view of the spindle 101 and the tool 102 attached thereto, viewed from the axial direction, conceptually illustrating the loads applied to the tool 102 during machining. The tool 102 has two blades 103 and 104 that are 180° out of phase with each other. Note that in FIGS. 4 to 6, the phase of the blade 103 of the tool 102 is set to 0°, and the phase of the blade 104 is set to 180°. When the tool 102 is rotated while machining a workpiece, loads F1 and F2 are applied to the blades 103 and 104 in the rotational direction. In FIG. 4, the tool 102 is attached to the spindle 101 in a normal state, i.e., with the rotation axis O1 of the spindle 101 and the axis O2 of the tool 102 aligned. In this case, only a load in the rotational direction around the rotation axis O1 (a load that tends to prevent rotation) is applied to the tool 102 during machining, and no load that moves the tool 102 parallel to the rotation axis O1 is generated.

[0009] 5 shows a state in which a foreign object 105 is caught between the outer peripheral surface of the tool 102 and the inner peripheral surface of the spindle 101 at a position where the phase is 180°, causing the axis O2 of the tool 102 to be misaligned in the direction of 0° (to the left in the figure) with respect to the rotation axis O1 of the spindle 101. Note that in FIG. 5, the amount of misalignment between the spindle 101 and the tool 102 is exaggerated (the same applies to FIG. 6, which will be described later). When machining is performed while the tool 102 in this state is rotated around the rotation axis O1 of the spindle 101, the load F1 applied to one blade 103 becomes larger than the load F2 applied to the other blade 104. Therefore, the resultant force of these loads F1 and F2 applies a load F3 that tends to translate the tool 102 in a direction perpendicular to the rotation axis O1 (downward in the figure).

[0010] 6 shows a state in which a foreign object 105 is caught between the outer peripheral surface of the tool 102 and the inner peripheral surface of the spindle 101 at a position where the phase is 270°, causing the axis O2 of the tool 102 to be shifted in the direction of 90° (upward in the figure) relative to the rotation axis O1 of the spindle 101. When machining is performed while rotating the tool 102 in this state around the rotation axis O1 of the spindle 101, the direction of the load F1 applied to one blade 103 and the direction of the load F2 applied to the other blade 104 are not parallel but are slightly inclined relative to each other, and therefore, the resultant force of these loads F1 and F2 applies a load F4 that tries to translate the tool 102 in a direction perpendicular to the rotation axis O1 (toward the left in the figure).

[0011] Incidentally, a machine tool typically has a positioning device (e.g., a servo motor) that positions the spindle 101 in three orthogonal directions (X, Y, and Z directions). As shown in FIG. 4, when machining is performed with the tool 102 properly attached to the spindle 101, no load is applied to the tool 102 in directions perpendicular to the rotation axis O1 (X and Y directions), and therefore no load is applied to the positioning device that positions the spindle 101 in these directions. On the other hand, as shown in FIGS. 5 and 6, when machining is performed with the tool 102 not properly attached to the spindle 101, loads F3 and F4 are applied to the tool 102 in directions perpendicular to the rotation axis O1, and these loads F3 and F4 are applied to the positioning device that positions the spindle 101 in the directions perpendicular to the rotation axis O1. Therefore, conversely, it is possible to determine whether the rotation axis O1 of the spindle 101 and the axis O2 of the tool 102 are aligned, i.e., whether the tool 102 is properly attached to the spindle 101, from the load applied to the positioning means that positions the spindle 101 in a direction perpendicular to the rotation axis O1.

[0012] It should be noted that this is not limited to the case where cutting is performed with tool 102 having two blades 103, 104 that are 180° out of phase with each other as described above, but also when cutting with a tool having a blade at one location in the circumferential direction or a tool having three or more blades evenly spaced in the circumferential direction, the load applied to the positioning means that positions the tool in a direction perpendicular to the rotation axis O1 differs depending on whether the attachment state of the tool to spindle 102 is good or bad. Therefore, even when using these tools, it is possible to determine whether the tool is properly attached to spindle 101 from the load applied to the positioning means that positions the tool in a direction perpendicular to the rotation axis O1, as described above.

[0013] Based on the above findings, the present invention provides a machine tool including a spindle to which a tool is attached and which rotates about a rotation axis, positioning means for positioning the spindle relative to a workpiece in a direction perpendicular to the rotation axis, load detection means for detecting a load applied to the positioning means, and abnormality determination means for determining the presence or absence of an abnormality based on a detection value detected by the load detection means.

[0014] The positioning means can be, for example, a servo motor. The servo motor has a built-in current detection unit that detects the value of the current flowing inside and a control unit that controls the motor output based on the detected current value. If the current detection unit of this servo motor is used as the load detection means, there is no need to provide a separate load detection means, which reduces costs. [Effects of the Invention]

[0015] As described above, according to the present invention, an abnormality in the attachment state of a tool to a spindle can be reliably detected using a low-cost method. [Brief explanation of the drawings]

[0016] [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] 10 is a graph showing the change over time in the current value of the motor of the X-direction feed means. [Figure 4] FIG. 1 is a schematic view of a spindle and a tool that are properly attached, as viewed from the axial direction. [Figure 5] FIG. 10 is a schematic view of a spindle and a tool mounted with a foreign object caught therein, as viewed from the axial direction. [Figure 6] FIG. 10 is a schematic view of a spindle and a tool mounted with a foreign object caught therein, as viewed from the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0018] 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 periphery (e.g., tool 102 shown in FIG. 4) or one with a cutting edge arranged at a single location around the periphery. 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 perpendicular to the Z direction and perpendicular to each other are referred to as the X direction and the Y direction, respectively.

[0019] 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.

[0020] 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 current flowing through the motor 14. In this embodiment, the motor 14 may further include a voltage detector 18 that detects the voltage within 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 external to the motor 14.

[0021] 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.

[0022] 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.

[0023] For example, if the tool 1 during machining deviates from its predetermined position in the X direction, 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.

[0024] For example, when machining a workpiece W with the tool 1 attached to the spindle 2 in a normal state, i.e., with the axis of the tool 1 aligned with the rotation axis of the spindle 2, only a load around the rotation axis is applied to the tool 1, and no load is applied that tries to translate the tool 1 in the XY plane (see FIG. 4). In this case, the tool 1 during machining is positioned at a predetermined position in the X and Y directions, so there is no need to correct the position of the tool 1 by the X-direction feed means 11 and the Y-direction feed means 12. Therefore, the current values ​​of the motors 14 of the X-direction feed means 11 and the Y-direction feed means 12 are relatively small.

[0025] On the other hand, when machining the workpiece W in a state where the axis of the tool and the rotation axis of the spindle 2 do not coincide, a load that tries to translate the tool 1 in the XY plane is generated (see load F3 in FIG. 5 and load F4 in FIG. 6). In this case, the tool 1 during machining deviates from its predetermined position in the X and Y directions, so current is supplied to the motor 14 of the X-direction feed means 11 and the motor 14 of the Y-direction feed means 12 to return the tool 1 to its predetermined position. Therefore, the current values ​​of the motors 14 of the X-direction feed means 11 and the Y-direction feed means 12 become relatively large.

[0026] Therefore, in this embodiment, while the tool 1 is machining the workpiece W (i.e., while the tool 1 is in contact with the workpiece W), one or both of the current values ​​of the motors 14 of the X-direction feed means 11 and the Y-direction feed means 12 are detected continuously or at predetermined intervals (for example, every 1 / 1000 seconds) by a current detection unit 17 serving as load detection means, and the detected current values ​​are transmitted to the control device 20. Based on the current values ​​of the motors 14 of the X-direction feed means 11 and / or Y-direction feed means 12 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.

[0027] FIG. 3 shows the time variation of the current value (black line indicated by "No Abnormal") of the motor 14 of the X-direction feed means 11 when machining is performed with the axis center of the tool 1 and the rotation axis center of the spindle 2 aligned, and the current value (gray line indicated by "Abnormal") detected by the current detection unit 17 of the motor 14 of the X-direction feed means 11 when machining is performed with the axis center of the tool 1 and the rotation axis center of the spindle 2 not aligned. As can be seen from this figure, the current value (in the illustrated example, the magnitude of the amplitude) of the motor 14 of the X-direction feed means 11 is significantly different between when there is no abnormality in the attachment state between the tool 1 and the spindle 2 and when there is. 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 either or both of the motor 14 of the X-direction feed means 11 and the motor 14 of the Y-direction feed means 12.

[0028] 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 average value of the current value of the motor 14 from the start to the end of machining is defined as A and the absolute value of the difference between the measured current value at each time and the average 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. 3, the amplitude of the current value indicated by the black line is always below threshold B from the start to the end of machining, so it is determined that there is no abnormality, whereas the amplitude of the current value indicated by the gray line exceeds threshold B, so it is determined that there is an abnormality.

[0029] Incidentally, even if the attachment state of the tool 1 and the spindle 2 is normal, a load in the X or Y direction may be momentarily applied to the tool 1 at the beginning or end of machining depending on the shape of the workpiece W, machining conditions, etc., causing the current value of the motor 14 of the X-direction feed means 11 or the Y-direction feed means 12 to momentarily jump up (see chain lines C and D in FIG. 3). In this case, if the determination is based on the threshold value B as described above, there is a risk that the abnormality determination means 26 will erroneously determine that "an abnormality has occurred" when detecting a current value such as that shown by chain lines C and D.

[0030] Therefore, 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 of at least one of the X-direction feed means 11 and the Y-direction feed means 12 over a period from the start of machining to the end of machining. Specifically, a threshold is set for the integrated value (i.e., the area of ​​the black or gray line in FIG. 3 ) of the amplitude of the current value of the motor 14 measured at predetermined intervals (e.g., every 1 / 1000 seconds) from the start of machining to the end of machining. Then, if the integrated value of the amplitude of the current value of the motor 14 exceeds the preset threshold, the abnormality determination means 26 determines that "an abnormality exists." As a result, even if the amplitude B of the current value momentarily increases as shown by the chain lines C and D in FIG. 3 , it is determined that "no abnormality exists" as long as the integrated value of the amplitude over the entire machining period is equal to or less than the threshold, thereby avoiding erroneous determination.

[0031] When integrating the amplitude of the current value of the motor 14 as described above, the amplitude may be simply integrated, or a value obtained by integrating a power (for example, the square) of the amplitude may be integrated. This makes it easier for the influence of a large amplitude to appear in the integrated value, thereby improving the reliability of the determination.

[0032] 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.

[0033] For example, the voltage detection unit 18 of the motor 14 of one or both of the X-direction feed means 11 and the Y-direction feed means 12 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 the motor 14 of one or both of the X-direction feed means 11 and the Y-direction feed means 12 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.

[0034] 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]

[0035] 1 tool 2 spindle 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 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

[Claim 1] a spindle to which a tool is attached and which rotates around a rotation axis; an X-direction positioning means for positioning the spindle relative to the workpiece in an X-direction perpendicular to the rotation axis; a Y-direction positioning means for positioning the spindle relative to the workpiece in a Y direction perpendicular to the rotation axis and the X direction; a load detection means for detecting a load applied to the X-direction positioning means and the Y-direction positioning means while machining is being performed by the tool; an abnormality determination means for determining whether or not there is an abnormality in the attachment state between the tool and the spindle based on the detection value detected by the load detection means, the X-direction positioning means and the Y-direction positioning means are servo motors each incorporating a current detection unit that detects a current value flowing therein and a control unit that controls an output based on the detected current value, the load detection means is the current detection unit built into the servo motor, the current detection unit detects a value of a current flowing inside the servo motor at predetermined intervals during a period from the start of machining by the tool to the end of machining, The abnormality determination means determines whether or not there is an abnormality in the attachment state of the tool and the spindle based on the integrated value of the squares of the current values ​​detected by the current detection units of the X-direction positioning means and the Y-direction positioning means during the period from the start of machining to the end of machining by the tool.

Images