Numerical control device

Abstract

A numerical control device is provided that can suppress abrupt changes in the angle of a rotation axis near a singular point and can accommodate any mechanical structure. The numerical control device numerically controls the indicated direction of an axis of a movable axis member using two or more rotation axes. The device comprises: a singular point distance calculation unit that calculates a singular point distance based on the rotation axis directions and indicated directions of the two or more rotation axes according to an operation command; a rotation axis extraction unit that extracts a control rotation axis for controlling the indicated direction based on the singular point distance calculated by the singular point distance calculation unit; and a pulse generation unit that generates pulses for driving the control rotation axis based on the control rotation axis extracted by the rotation axis extraction unit. The rotation axis extraction unit compares the singular point distance with a preset threshold to extract a rotation axis exceeding the threshold as the control rotation axis, or compares the singular point distances with each other to extract a rotation axis having a larger singular point distance as the control rotation axis.

Description

Technical Field

[0001] The invention relates to a numerical control device. Background Art

[0002] Five-axis machining centers are known that utilize two or more rotary axes in addition to the three linear axes (X, Y, and Z) to machine a workpiece mounted on a table. Examples of such five-axis machining centers include those with two rotary axes (A and C) located on the workpiece side and those with two rotary axes (A and C) located on the tool side. Machines with two rotary axes located on the tool side sometimes also have an inclined rotary axis located on the workpiece side.

[0003] In numerical control systems for five-axis machining centers, posture control is required by rotating the tool orientation according to command values for workpiece machining instructions, or by correcting the tool orientation during workpiece setup error correction or three-dimensional rotation error correction. Tool orientation refers to the relative orientation of the tool with respect to the workpiece. Posture control involves calculating the rotation angles of each rotation axis to achieve the desired tool orientation vector based on the desired tool orientation vector, thereby controlling the tool orientation, which represents the tool posture.

[0004] Currently, the following technology is described in Patent Document 1: In a numerical control device that controls a 5-axis machining center, correction amounts corresponding to four errors, namely, a linear axis-dependent translation error depending on the linear axis position, a rotary axis-dependent translation error depending on the rotary axis position, a linear axis-dependent rotation error depending on the linear axis position, and a rotary axis-dependent rotation error depending on the rotary axis position, are set. Based on these correction amounts, a translation correction amount is calculated and added to the commanded linear axis position, and a rotation correction amount is calculated and added to the rotary axis position, thereby enabling machining to be performed with the commanded tool posture.

[0005] Patent document 2 describes the following technology: in a numerical control device that numerically controls a machine tool having a linear axis and a rotary axis, the tool tip position is moved to a position without error, and the tool posture in a direction that can be reasonably corrected is maintained in an error-free posture, thereby achieving high-precision machining.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Patent No. 4837115

[0009] Patent Document 2: Patent No. 5105024 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] In tool posture control for a five-axis machine tool, the angle of the rotation axis sometimes fluctuates extremely sharply near a singular point, causing the rotational speed or acceleration of the rotation axis to become extremely high. An example of a singular point is a point where the tool orientation coincides with the direction of the rotation axis. At this singular point, even if the rotation axis is changed, the tool orientation remains largely unchanged. In tool posture control for a five-axis machine tool, if the rotation axis rotates rapidly near a singular point while passing through it, this can degrade the surface quality of the workpiece.

[0012] However, the technique described in Patent Document 1 does not solve the aforementioned problem of a sudden change in the rotation axis angle near a singular point. Therefore, in the technique described in Patent Document 1, a sudden change in the rotation axis angle due to error correction may occur near a singular point.

[0013] In contrast, the technology described in Patent Document 2 can correct three-dimensional rotation errors in the tool orientation using only errors that do not cause the aforementioned singular point problem. However, the technology described in Patent Document 2 is limited in orientation by a mechanical structure that does not change in the machine coordinate system, resulting in an inability to correct errors around a specific rotation axis.

[0014] Therefore, a numerical control device that can suppress a sudden change in the angle of the rotation axis near a singular point and can also cope with any mechanical structure is desired.

[0015] Means for solving problems

[0016] One embodiment of the present disclosure is a numerical control device for numerically controlling the indicated direction of an axis of a movable axis member using two or more rotation axes, the device comprising: a singular point distance calculation unit for calculating a singular point distance, which is a distance to a singular point, based on the rotation axis directions of each of the two or more rotation axes and the indicated direction according to an operation command; a rotation axis extraction unit for extracting a control rotation axis that controls the indicated direction from the two or more rotation axes based on the singular point distance calculated by the singular point distance calculation unit; and a pulse generation unit for generating a pulse for driving the control rotation axis based on the control rotation axis extracted by the rotation axis extraction unit. The rotation axis extraction unit compares the singular point distance with a preset threshold value to extract, as the control rotation axis, the rotation axis exceeding the threshold value from the two or more rotation axes, or compares the singular point distances to extract, as the control rotation axis, the rotation axis having a larger singular point distance from the two or more rotation axes.

[0017] Effects of the Invention

[0018] According to one embodiment of the present disclosure, it is possible to provide a numerical control device that can suppress a sudden change in the angle of a rotation axis near a singular point and can also cope with any mechanical structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a perspective view showing one embodiment of a five-axis machining center numerically controlled by a numerical controller.

[0020] Figure 2 This is a perspective view showing one embodiment of a six-axis machining center numerically controlled by a numerical controller.

[0021] Figure 3 This is a functional block diagram illustrating one embodiment of a numerical control device.

[0022] Figure 4A This is an explanatory diagram illustrating the singularity distance.

[0023] Figure 4B This is an explanatory diagram illustrating the singularity distance.

[0024] Figure 5 This is a functional block diagram illustrating another embodiment of a numerical controller.

[0025] Figure 6A The trajectory of the tool direction due to the rotation of the singular point rotation axis not controlled by the third pulse generating unit will be described.

[0026] Figure 6B The trajectory of the tool direction based on the rotation of the singular point rotation axis controlled by the third pulse generating unit will be described. DETAILED DESCRIPTION

[0027] Hereinafter, a numerical control device according to one embodiment of the present disclosure will be described with reference to the accompanying drawings. Figure 1 and Figure 2 The specific structure of a processing machine numerically controlled by a numerical controller will be described.

[0028] Figure 1The 5-axis processing machine 1 is shown. The 5-axis processing machine 1 has a bed 11, a pair of column parts 12, 12 vertically arranged on the bed 11, and a guide rail part 13 connecting the upper ends of the column parts 12, 12 to each other and extending laterally. A tool head 14 is installed on the guide rail part 13. The 5-axis processing machine 1 sets the X axis in the surface direction of the bed 11 and along the longitudinal direction of the guide rail part 13, the Y axis in the surface direction of the bed 11 and orthogonal to the longitudinal direction of the guide rail part 13, and the Z axis in the direction perpendicular to the surface direction of the bed 11 as linear axes. The tool head 14 is provided so as to be able to move linearly along these three axes, namely, the X axis, the Y axis, and the Z axis. At the lower end of the tool head 14, a tool 15 as a movable axis component protrudes downward along the Z axis direction. Figure 1 In FIG. 1 , St represents a tool direction that is an indication direction of an axis of the tool 15 .

[0029] The bed 11 of the 5-axis machining center 1 is provided with a loading portion 16 for loading the workpiece W to be machined and rotating the workpiece W around the C-axis, and a rotating table 17 for rotating the loading portion 16 around the A-axis along the X-axis direction. When the loading portion 16 is configured to be perpendicular to the Z-axis (when the rotation angle of the rotating table 17 is 0°), the C-axis is configured to be parallel to the Z-axis direction. These two axes, the A-axis and the C-axis in the 5-axis machining center 1, are configured on the side of the workpiece W and are the rotation axes that determine the relative orientation of the tool 15 relative to the workpiece W, that is, the tool direction, by rotating. Figure 1 In the figure, S1 represents the rotation axis of the A-axis. S2 represents the rotation axis of the C-axis.

[0030] Figure 2 The figure shows a six-axis machining center 2. The six-axis machining center 2 includes a bed 21, a pair of columns 22, 22 erected on the bed 21, and a guide rail 23 connecting the upper ends of the columns 22, 22 and extending laterally. A tool head 24 is mounted on the guide rail 23. The six-axis machining center 2 has an X-axis extending along the surface of the bed 21 and along the longitudinal direction of the guide rail 23, a Y-axis extending along the surface of the bed 21 and perpendicular to the longitudinal direction of the guide rail 23, and a Z-axis perpendicular to the surface of the bed 21 as linear axes. The tool head 24 is configured to be linearly movable along each of these three axes: the X-axis, the Y-axis, and the Z-axis.

[0031] A tool 25 serving as a movable axis component is provided at the lower end of the tool head 24. Specifically, a first rotating portion 26 is provided at the lower end of the tool head 24, which rotates the tool 25 in a manner of swinging around the A axis along the X-axis direction; and a second rotating axis 27 is provided, which rotates the first rotating portion 26 around the C axis along the Z-axis direction. These two axes, the A axis and the C axis in the 5-axis processing machine 2, are arranged on the tool 25 side, and are rotating axes that determine the relative orientation of the tool 25 relative to the workpiece W, that is, the tool direction, by rotation. A workbench 28 for carrying the workpiece W, which is the object to be processed, is provided on the bed 21. The workbench 28 is configured to be rotatable by a third rotating portion 29 that is tilted relative to the surface direction of the bed 21. Figure 2 , S1 represents the rotation axis of the A-axis, S2 represents the rotation axis of the C-axis, and S3 represents the rotation axis of the third rotating portion 29 serving as an inclined rotation axis.

[0032] Figure 3 It is a functional block diagram illustrating an embodiment of a numerical control device. In the numerical control device 100, the instruction analysis unit 101 analyzes the machining program for machining the workpiece W and converts it into an execution form. The instruction analysis unit 101 outputs the analysis result converted into the execution form to the interpolation unit 102. The interpolation unit 102 performs interpolation processing on the analysis result of the execution form sent from the instruction analysis unit 101, and generates a movement instruction including error correction for each axis of the 5-axis machining center 1 and the 6-axis machining center 2. The interpolation unit 102 outputs the generated movement instruction of each axis to the pulse generation unit 103. The pulse generation unit 103 generates a drive pulse for driving each axis based on the movement instruction of each axis sent from the interpolation unit 102. The pulse generation unit 103 outputs the generated drive pulse to the servo control unit of each axis. In Figure 3 103, only the A-axis servo control unit 14a and the C-axis servo control unit 14b are shown. The servo control units for the other X-axis, Y-axis, Z-axis, and tilt-rotation axes are not shown. The servo control units for each axis rotate the motor (not shown) for each axis in response to drive pulses sent from the pulse generator 103.

[0033] The numerical controller 100 also includes a singular point distance calculation unit 105 and a rotation axis extraction unit 106. The singular point distance calculation unit 105 calculates the singular point distance, which is the distance to the singular point, based on the rotation axis direction and the tool orientation. Specifically, the singular point distance calculation unit 105 receives the rotation angles of each rotation axis (i.e., the rotation axis direction) and the tool orientation after interpolation processing from the interpolation unit 102, and calculates the singular point distance based on these rotation axis directions and the tool orientation.

[0034] Here, the singular point distance is explained. The singular point distance is obtained by taking the outer product of the rotation axis direction and the tool direction. Figure 4A and Figure 4B Further specific explanation. Figure 4A and Figure 4B The two rotation axes are represented by the A-axis (rotation axis S1) and the C-axis (rotation axis S2). St represents the tool direction. The singular point distance of rotation axis S1 is represented by d1, and the singular point distance of rotation axis S2 is represented by d2. In this case, the singular point distances d1 and d2 are calculated as follows. The system singular point distance d3 is the singular point distance of the entire processing machine, which is the sum of the rotation axes S1 and S2.

[0035] [Formula 1]

[0036] Singular point distance of rotation axis S1:

[0037] Singular point distance of rotation axis S2:

[0038] The singularity distance of the system:

[0039] The singular point distance d1 of the rotation axis S1 is the amount of change in the tool direction St when the rotation axis S1 rotates around the A axis. The singular point distance d2 of the rotation axis S2 is the amount of change in the tool direction St when the rotation axis S2 rotates around the C axis. Figure 4A In the example, the singular point distance d1 of the rotation axis S1 is almost the same as the singular point distance d2 of the rotation axis S2. Figure 4B In the figure, the singular point distance d2 of the rotation axis S2 is smaller than the singular point distance d1 of the rotation axis S1. When the singular point distance is small, the tool direction hardly changes even if the rotation axis rotates. The singular point is a point where the tool direction is not affected even if the rotation axis changes. Therefore, a small singular point distance value can be judged as a close distance to the singular point. In other words, it can be judged that Figure 4B The rotation axis S2 is shown to be closer to the singular point than the rotation axis S1.

[0040] The singular point distance calculation unit 105 calculates the singular point distances based on the rotation axis directions and tool directions of the respective rotation axes sent from the interpolation unit 102 , and then outputs the singular point distances to the rotation axis extraction unit 106 .

[0041] The rotation axis extraction unit 106 extracts a control rotation axis from two or more rotation axes by comparing the singular point distances of the rotation axes sent from the singular point distance calculation unit 105. The control rotation axis is a rotation axis that is rotationally controlled to control the tool direction.

[0042] Specifically, the rotation axis extraction unit 106 compares the singular point distances of each rotation axis sent from the singular point distance calculation unit 105 with a pre-set threshold and extracts the rotation axis that exceeds the threshold from among two or more rotation axes as the control rotation axis. For example, in a five-axis machine tool 1 having two rotation axes, rotation axis S1 and rotation axis S2, if the singular point distance d1 of rotation axis S1 is below the threshold and the singular point distance d2 of rotation axis S2 exceeds the threshold, the rotation axis extraction unit 106 does not extract rotation axis S1 as the control rotation axis and extracts only rotation axis S2 as the control rotation axis. Furthermore, if the singular point distance d3 is below the threshold, it is assumed that the rotational directions of rotation axes S1 and S2 are substantially the same. In this case, to uniquely determine the angle solution for each rotation axis S1 and S2, if the singular point distance d2 of rotation axis S2 and the singular point distance d1 of rotation axis S1 exceed the threshold, rotation axis S1, the rotation axis closest to the tool, is extracted as the control rotation axis. The rotation axis extraction unit 106 outputs information on the extracted controlled rotation axis to the pulse generation unit 103 .

[0043] The pulse generating unit 103 generates a driving pulse for driving the control rotating axis based on the control rotating axis extracted by the rotating axis extracting unit 106. Specifically, Figure 3 As shown, the pulse generation unit 103 includes a first pulse generation unit 103a. When the rotation axis extraction unit 106 extracts only one controlled rotation axis, the first pulse generation unit 103a outputs correction pulses based on error correction only for the one controlled rotation axis extracted by the rotation axis extraction unit 106. For rotation axes not extracted by the rotation axis extraction unit 106, the first pulse generation unit 103a temporarily stops outputting correction pulses based on error correction. Thus, when passing through a singular point, only the one controlled rotation axis extracted by the rotation axis extraction unit 106 is driven to closely match the tool orientation specified by the machining command.

[0044] For example, if the singular point distance d1 of rotation axis S1 is below a threshold value, and the singular point distance d2 of rotation axis S2 exceeds the threshold value, the first pulse generator 103a temporarily stops outputting correction pulses for error correction of rotation axis S1 and performs error correction by rotating only rotation axis S2, which serves as the control rotation axis. In this case, the first pulse generator 103a calculates the correction amount that best eliminates the remaining error using only rotation axis S2, which is capable of error correction, and generates a corresponding drive pulse.

[0045] Specifically, the first pulse generating unit 103 a first calculates the tool direction error based on the rotation errors a, b, and c shown below, for example.

[0046] [Formula 2]

[0047]

[0048] Next, as shown below, the correction amount α1 of the rotation axis S1 at the time when the updating is temporarily stopped is added.

[0049] [Formula 3]

[0050]

[0051] Next, as shown below, the correction amount α2 of the rotation axis S2 , which is the controlled rotation axis for which error correction is effective, is calculated.

[0052] [Formula 4]

[0053]

[0054] When passing through a singular point, the first pulse generator 103a generates a drive pulse corresponding to the calculated correction amount α2 for the rotation axis S2, which serves as the controlled rotation axis. Thus, when machining a workpiece W using the rotation axes S1 and S2 in addition to the three axes X, Y, and Z, error correction is performed only on the rotation axis S2, whose distance from the singular point is greater than a threshold, to control the tool direction when passing through the singular point.

[0055] Therefore, according to the numerical controller 100, when there are two rotation axes, error correction is performed only using the control rotation axis extracted by the rotation axis extraction unit 106. This prevents abrupt changes in the rotation axis angle near the singular point and allows for compatibility with any mechanical structure. Rotational errors in all directions outside the singular point can be corrected, eliminating the problem of errors around a specific axis being unable to be corrected. Furthermore, since no restrictions are placed on the drive pulses, processing speed is not reduced.

[0056] In the numerical control device 100, as Figure 2 As shown, when the processing machine is a six-axis processing machine 2 having three rotation axes S1, S2, and S3, the singular point distance calculation unit 105 can also calculate the singular point distances d12, d23, and d31 by combining the three rotation axes S1, S2, and S3 as shown below.

[0057] [Formula 5]

[0058] Singular point distance of combination 1 (rotation axis S1, rotation axis S2):

[0059]

[0060] Singular point distance of combination 2 (rotation axis S2, rotation axis S3):

[0061]

[0062] Singular point distance of combination 3 (rotation axis S3, rotation axis S1):

[0063]

[0064] In this case, the rotation axis extraction unit 106 compares the multiple singular point distances sent from the singular point distance calculation unit 105 and extracts the rotation axis with the largest singular point distance from the two or more rotation axes as the control rotation axis. In the case of the singular point distances d12, d23, and d31 described above, the rotation axis extraction unit 106 selects the singular point distance with the largest value among these singular point distances d12, d23, and d31 and extracts the combination of rotation axes corresponding to this singular point distance as the control rotation axis. For example, if the singular point distance d12 has the largest value among the singular point distances d12, d23, and d31, the rotation axis extraction unit 106 extracts the two rotation axes S1 and S2 corresponding to this singular point distance d12 as the control rotation axes.

[0065] like Figure 3 As shown, the pulse generator 103 includes a second pulse generator 103b. When the rotation axis extraction unit 106 extracts two controlled rotation axes, the second pulse generator 103b generates drive pulses for each of the two controlled rotation axes, thereby maximizing the tool orientation indicated by the machining command. In this case, since two of the three rotation axes are extracted as controlled rotation axes, the rotation axes do not become singular points. This further improves machining accuracy and reduces machining time.

[0066] Figure 5 This is a functional block diagram illustrating another embodiment of a numerical control device. In this numerical control device 100A, a third pulse generating unit 103c is added to the pulse generating unit 103. In addition, the rotation axis extracting unit 106 is configured to extract the singular point rotation axis in addition to the control rotation axis. Other structures are similar to Figure 3 The structures of the numerical control devices 100 shown are the same, so their detailed descriptions are omitted.

[0067] When the rotation axis extraction unit 106 compares the singular point distance with a threshold, it extracts the rotation axis whose singular point distance is within the threshold as the singular point rotation axis. For example, if there are two rotation axes, rotation axis S1 and rotation axis S2, and the singular point distance d1 of rotation axis S1 exceeds the threshold, the rotation axis extraction unit 106 extracts only the rotation axis S1, whose singular point distance d1 exceeds the threshold, as the control rotation axis. In this case, the rotation axis extraction unit 106 extracts the other rotation axis S2, which was not extracted as the control rotation axis, as the singular point rotation axis whose singular point distance d2 is within the threshold. When passing through a singular point, the third pulse generation unit 103c of the pulse generation unit 103 generates a drive pulse for the singular point rotation axis extracted by the rotation axis extraction unit 106, different from the drive pulse for the control rotation axis, to rotate the axis to a predetermined angle.

[0068] use Figure 6A as well as Figure 6B The driving of the singular point rotation axis will be described. Figure 6A and Figure 6B The tool directions Sy and Sx when controlling a singular point rotation axis are shown. The center point is the singular point. The circle centered on the singular point represents the threshold used by the rotation axis extraction unit 106 to compare the distance to the singular point when extracting a control rotation axis. A singular point rotation axis not extracted as a control rotation axis causes the tool direction to move from a commanded start point to a commanded end point, where the commanded start point and the commanded end point are located outside the threshold range across the singular point.

[0069] Figure 6A This indicates that the third pulse generator 103c is not controlling the singular point rotation axis. In this case, the tool direction passes through the singular point while moving from the control starting point to the end point within the threshold range. In this case, there is a case where the rotation axis changes suddenly. In contrast, Figure 6B As shown, when the singular point distance d2 of the rotation axis S2 falls within a threshold value, thus becoming the singular point rotation axis, the third pulse generator 103c controls the rotation of the singular point rotation axis so that it rotates by a pre-specified angle. The pre-specified angle is smaller than the maximum allowable angle of the rotation axis extracted as the singular point rotation axis (here, the rotation axis S2). The third pulse generator 103c rotates the singular point rotation axis by the pre-specified angle. As a result, the singular point rotation axis slowly begins to rotate when it falls within the threshold value, allowing the tool to move to the end point, avoiding the singular point.

[0070] Specifically, the third pulse generator 103c obtains the commanded endpoint tool direction from the command analyzer 101. Based on the obtained tool direction, the third pulse generator 103c calculates the commanded endpoint angle Ce of the singular point rotation axis. Furthermore, the third pulse generator 103c obtains the current angle Cn of the singular point rotation axis from the interpolator 102. Based on the parameter settings, the third pulse generator 103c calculates the maximum rotation pulse δCmax, which is the maximum allowable value of the drive pulses required to rotate the singular point rotation axis.

[0071] The singular point distance calculation unit 105 calculates the singular point distance at the command endpoint for the singular point rotation axis. The rotation axis extraction unit 106 confirms whether the singular point distance at the command endpoint of the singular point rotation axis exceeds a threshold. If the rotation axis extraction unit 106 confirms that the singular point distance at the command endpoint of the singular point rotation axis exceeds the threshold, it then confirms that the singular point distance of the current singular point rotation axis is within the threshold.

[0072] When the current singular point distance of the singular point rotation axis is within the threshold, the third pulse generator 103 c generates a drive pulse for rotating the singular point rotation axis as follows, regardless of the interpolated command value obtained by interpolating between the command values.

[0073] Ce-Cn>0

[0074] a. When Ce-Cn>δCmax, rotate the singular point rotation axis by δCmax.

[0075] b. When Ce-Cn<δCmax, the singular point rotation axis is rotated by Ce-Cn.

[0076] When Ce-Cn<0

[0077] a. When -(Ce-Cn)>δCmax, the singular point rotation axis is rotated by -δCmax.

[0078] b. When -(Ce-Cn)<δCmax, the singular point rotation axis is rotated by Ce-Cn.

[0079] Therefore, in Figure 6B As shown by the dotted line, the singular point rotation axis slowly starts rotating when it enters the threshold, so that the tool direction avoids the singular point and moves to the end point. This can avoid sudden angular changes in the rotation axis that would reduce the surface quality of the workpiece W.

[0080] In the above embodiments, the tools 15 and 25 used to machine the workpiece W in the five-axis machine tool 1 and the six-axis machine tool 2 are exemplified as movable axis members. However, the movable axis member is not limited to the tools 15 and 25, as long as it is an axis member that is movable in a direction indicated by the longitudinal direction of the axis, i.e., an indicated direction, controlled by a numerical controller. The movable axis member may be, for example, a probe (not shown) provided in the machine tool.

[0081] In the above embodiment, the singular point distance calculation unit 105 is configured to calculate the singular point distances based on the rotational axis directions of the two or more rotational axes and the tool direction in accordance with the machining command for the workpiece W. However, the singular point distance calculation unit 105 may also be configured to calculate the singular point distances based on the rotational axis directions of the two or more rotational axes and the indicated direction of the axis of the moving axis component in accordance with an operation command other than the machining command, such as an operation command based on a machine movement command.

[0082] Description of Reference Signs

[0083] 100, 100A numerical control device

[0084] 105 Singularity Distance Calculation Unit

[0085] 106 Rotation axis extraction unit

[0086] 103 Pulse Generation Unit

[0087] 103a First pulse generating unit

[0088] 103b Second pulse generating unit

[0089] 103c Third pulse generating unit

[0090] S1, S2, S3 rotation axes

[0091] St tool direction

[0092] W workpiece.

Claims

1. A numerical control device that numerically controls the indicated direction of an axis of a movable axis member through two or more rotating axes, characterized in that: The numerical control device comprises: a singular point distance calculation unit for calculating a singular point distance, which is a distance to each singular point, based on the rotation axis directions of each of the two or more rotation axes based on the motion command and the indicated direction; a rotation axis extraction unit that extracts a control rotation axis for controlling the indicated direction from the two or more rotation axes based on the singular point distance calculated by the singular point distance calculation unit; as well as a pulse generating unit that generates a pulse for driving the controlled rotating axis based on the controlled rotating axis extracted by the rotating axis extracting unit, The singular point is a point near which the angle of the rotation axis changes significantly and the rotation speed or acceleration of the rotation axis increases. The singular point distance is the change in the tool direction when the rotation axis rotates around its axis. The rotation axis extraction unit compares the singular point distance with a preset threshold value and extracts the rotation axis exceeding the threshold value from among the two or more rotation axes as the control rotation axis, or compares the singular point distances with each other and extracts the rotation axis having the larger singular point distance from among the two or more rotation axes as the control rotation axis.

2. The numerical control device according to claim 1, wherein The pulse generating unit includes: a first pulse generating unit for generating, when only one of the control rotation axes is extracted by the rotation axis extracting unit, a driving pulse for driving the one control rotation axis so as to approach the indicated direction indicated by the motion instruction most closely via only the one control rotation axis; as well as A second pulse generating unit generates drive pulses for driving each of the two controlled rotary axes so as to approach the indicated direction indicated by the operation command when the two controlled rotary axes are extracted by the rotary axis extracting unit.

3. The numerical control device according to claim 1 or 2, characterized in that: When comparing the singular point distance with the threshold, the rotation axis extraction unit extracts the rotation axis whose singular point distance is within the threshold as the singular point rotation axis. The pulse generating unit includes a third pulse generating unit that generates a drive pulse for driving the singular point rotation axis so as to rotate the singular point rotation axis to a predetermined angle.

Images