JP2008090734A - Numerical control apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a numerical control apparatus capable of smoothly and stably operating a tool even at a singular point and before and after the singular point, suppressing the occurrence of unnecessary degradation in motion accuracy, maintaining high working accuracy, and performing stable working without causing tool damage or excess tool wear. <P>SOLUTION: The numerical control apparatus for controlling a driving shaft of a machine so that a cutting point where the bottom of the tool contacts with a workpiece is moved along a moving route commanded by a working program while changing tool attitude against the workpiece interpolates the center point of a tool tip or a machine position in a section including the singular point when a working surface passes the singular point vertical to the tool and driven. Further, working surface normal vectors on the start point and end point of the section including the singular point, a tool axis direction vector, or both of them are corrected so as to be approached to relative positional relation between working surface normal vectors of a section including no singular point and the tool axis direction vector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a numerical control device (hereinafter referred to as NC), and more particularly to a numerical control device for a machine tool having a three-dimensional tool radius correction function when machining at the edge of a tool while changing the posture of the tool with respect to a workpiece. .

  In a numerically controlled machine tool, machining may be performed while changing the posture of the tool with respect to the workpiece (direction of the tool axis). A typical example is simultaneous 5-axis machining with a 5-axis machine. The machining performed while changing the posture of the tool may be performed mainly on the side surface of the tool or mainly on the bottom surface of the tool.

  When machining at the edge of the bottom surface of the tool while changing the posture of the tool, if the movement path commanded to the machining program can be corrected by the NC based on the value obtained by accurately measuring the diameter of the tool used at the site, Efficient because there is no need to recreate the machining program each time. As a conventional three-dimensional tool radius correction method corresponding to bottom machining, the tool radius correction direction is calculated from the tool advance direction (motion vector) and the tool axis direction vector commanded to the machining program. Multiplying the tool radius by the tool radius has been proposed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 07-036514

  Hereinafter, problems in the conventional three-dimensional tool diameter correcting method will be described using examples. Consider an example in which a square end mill is used as a tool as shown in FIG. As shown in FIG. 1A or 1C, when the tool 101 is inclined with respect to the machining surface 100, one point where the tool 101 contacts the machining surface 100 (hereinafter referred to as a cutting point Pe). Is uniquely determined. However, in the state where the tool 101 is perpendicular to the machining surface 100 as shown in FIG. 4B, the entire bottom surface of the tool 101 is in contact with the tool 101 instead of one point, and therefore the cutting point Pe is not uniquely determined. . A state in which the tool axis direction vector W is perpendicular to the machining surface 100 as shown in FIG. 5B is called a singular point (or singular posture) in the three-dimensional tool radius correction.

  If such a singular point is passed during the movement, the position of the cutting point Pe viewed from the tool 101 will change abruptly before and after passing the singular point in the above-described conventional method, which adversely affects the machine and processing. Effect. For example, as shown in FIG. 2, the cutting point Pe follows a command path 102 instructed by the machining program while continuously changing the posture of the tool 101 with respect to the machining surface 100 from the start point (b1) to the end point (b10). And moving at a constant speed. It moves in the order of (b1), (b2), (b3),..., (B10) from the start point to the end point, but at a certain point S between (b5) and (b6), the tool axis direction The vector W becomes perpendicular to the machining surface 100 (that is, passes through a singular point). The period from (b1) to (b5) is a state in which the tool 101 advances while tilting forward with respect to the machining surface 100, and the cutting point Pe is a forward angle of the tool 101 in the traveling direction (the tool 101 in the figure). At the lower right corner).

  On the other hand, during the period from (b6) to (b10), the tool 101 is in a state of moving backward with respect to the machining surface 100, and the cutting point Pe is a rear angle in the traveling direction of the tool 101 (which can be said in the drawing). The lower left corner of the tool). Before and after passing through the singular point ((b5) and (b6)), the position of the cutting point Pe viewed from the tool 101 changes steeply from the front corner in the traveling direction to the rear corner in the traveling direction. Along with this, a tool radius correction vector ΔPcomp (a white arrow in the figure), which is a vector from the cutting point Pe to the tool tip center point Pc, also changes discontinuously in a substantially opposite direction before and after passing through the singular point. That is, the tool 101 moves steeply about the tool diameter before and after the singular point. In order to move the tool 101 abruptly in this way, the machine needs to move suddenly, which causes an overload of the motor, vibration of the machine, and an increase in servo following error, and failure of the control device or machine or an alarm. This causes problems such as a decrease in productivity due to the stop and a deterioration in machining accuracy due to an increase in motion error. In addition, the sharp movement of the tool 101 with respect to the processing surface 100 causes a sudden change in cutting resistance, which causes a problem of tool damage such as chipping and excessive tool wear.

  In the above-described example shown in FIGS. 1 and 2, the tool 101 is an example of a square end mill whose bottom edge is a square shape. However, as shown in FIG. 3, the edge is round like a radius end mill. In the tool 101 as well, if there is even a flat part on the bottom surface of the tool (that is, if the entire tool bottom surface is not a hemispherical ball end mill), the tool axis direction vector is perpendicular to the machining surface 100 (singular Since the tool 101 moves abruptly by the diameter of the flat portion on the bottom surface of the tool before and after the point), the same problem occurs.

  The present invention was made to solve such problems, and operates smoothly and stably at the singular point and before and after the singular point, without causing unnecessary deterioration in motion accuracy, and can maintain high processing accuracy. Another object of the present invention is to obtain a numerical control device that can perform stable machining without causing tool damage or excessive tool wear.

  The present invention uses a square end mill tool or a radius end mill tool so that the cutting point at which the bottom surface of the tool contacts the workpiece moves along the movement path commanded by the machining program while changing the tool posture with respect to the workpiece. A numerical control device for controlling a drive shaft of a machine, based on movement data instructed by the machining program and tool data of a tool to be used, with respect to a machining surface of the workpiece during movement of the tool. A singular point determination unit that determines whether or not there is a singular point whose tool axis direction is vertical, and when the singular point determination unit determines that there is a singular point during movement, the movement data is A movement data correction unit that divides a movement section that includes a movement section that does not include a singular point, and a movement that includes the singular point among movement sections divided by the movement data correction unit. If there is movement, the position of the tool tip center point is interpolated and obtained. On the other hand, in the movement section that does not include the singular point, the cutting point position is interpolated to obtain the machining surface normal vector and the tool axis. An interpolation unit that obtains a tool radius correction vector from the direction to the tool tip center point to obtain a tool tip center point and obtains the position of each machine axis from the obtained tool tip center point using an inverse kinematic function And a position control unit that controls the drive axis of the machine according to the position of each axis of the machine determined by the interpolation unit.

  The present invention uses a square end mill tool or a radius end mill tool so that the cutting point at which the bottom surface of the tool contacts the workpiece moves along the movement path commanded by the machining program while changing the tool posture with respect to the workpiece. A numerical control device for controlling a drive shaft of a machine, based on movement data instructed by the machining program and tool data of a tool to be used, with respect to a machining surface of the workpiece during movement of the tool. A singular point determination unit that determines whether or not there is a singular point whose tool axis direction is vertical, and when the singular point determination unit determines that there is a singular point during movement, the movement data is A movement data correction unit that divides a movement section that includes a movement section that does not include a singular point, and a movement that includes the singular point among movement sections divided by the movement data correction unit. If there is movement, the position of the tool tip center point is interpolated and obtained. On the other hand, in the movement section that does not include the singular point, the cutting point position is interpolated to obtain the machining surface normal vector and the tool axis. An interpolation unit that obtains a tool radius correction vector from the direction to the tool tip center point to obtain a tool tip center point and obtains the position of each machine axis from the obtained tool tip center point using an inverse kinematic function And a position control unit that controls the drive axis of the machine according to the position of each axis of the machine determined by the interpolation unit, and operates smoothly and stably at the singular point and before and after the singular point. In addition, unnecessary deterioration of the movement accuracy does not occur, high machining accuracy can be maintained, and stable machining can be performed without causing tool damage or excessive tool wear.

Embodiment 1 FIG.
[Correct surface normal vector]
FIG. 4 is a block diagram showing the configuration of the numerical control apparatus according to Embodiment 1 of the present invention. The numerical control apparatus according to the first embodiment uses a square end mill tool or a radius end mill tool to change a tool posture with respect to a workpiece while a cutting point at which the tool bottom surface comes into contact with the workpiece is a movement path commanded to the machining program ( The numerical control device controls the drive shaft of the machine so as to move along a path specified by movement data described later. In this embodiment, in the case of simultaneous 5-axis machining with a 5-axis machine, machining is performed while changing the posture of the tool, and a case where machining is performed mainly on the bottom surface of the tool will be described as an example. As shown in FIG. 4, the numerical control apparatus according to the first embodiment includes a machining program 1, tool data 3, a singular point determination unit 4, a movement data correction unit 6, an interpolation unit 8, and a display unit 10. And position control units 1 to 5 (reference numerals 12 to 16) for controlling the first to fifth axes. In FIG. 4, 2 is movement data instructed to the machining program 1, 5 is a singular point determination result output from the singular point determination unit 4, and 7 is corrected movement data output from the movement data correction unit 6. , 9 are current positions output from the interpolation unit 8, and 11 is a position command value output from the interpolation unit 8. These are described in detail below.

  The singular point determination unit 4 determines whether there is a singular point on the movement path in the movement of each block from the movement data 2 instructed to the machining program 1 and the tool data 3 of the tool to be used. Is output as the singularity determination result 5. Further, the movement data correction unit 6 corrects the movement data 2 from the movement data 2, the tool data 3, and the singular point determination result 5 and outputs corrected movement data 7. The interpolation unit 8 performs interpolation based on the corrected movement data 7 and the tool data 3, and outputs a position command value 11 for each axis. Here, the interpolation unit 8 performs not only interpolation but also coordinate conversion according to acceleration / deceleration and machine axis configuration. The interpolation unit 8 calculates the current position 9 and sends it to the display unit 10 for display. For the calculation of the current position 9, the movement data 2 before correction may be used. Position control units 1 to 5 (reference numerals 12 to 16) of each axis are, for example, position control sections 1 to 3 (reference numerals 12 to 14), three orthogonal axes for changing the position of the tool with respect to the workpiece, position control. Parts 4 to 5 (reference numerals 15 to 16) are two rotation axes (for example, an A axis and a C axis) for changing the posture of the tool with respect to the workpiece. These five position control units 1 to 5 (reference numerals 12 to 16) servo-control a drive system (not shown) based on the respective position command values 11, thereby moving a 5-axis processing machine (not shown) to the workpiece. Then move the tool and process it.

  Next, the operation will be described. The tool data 3 is data including a tool type (square end mill, radius end mill), a radius value d of the tool outer diameter, a round corner radius (corner radius) r, and a tool length h as shown in FIG. The present invention is a method for solving the problem of the singular point in the three-dimensional tool radius correction. The problem of the singular point in the three-dimensional tool radius correction is that the bottom surface of the rotary tool is flat (this is perpendicular to the tool axis direction). Therefore, these tools are subject to the correction of the movement data 2 and other tools (for example, ball end mills) are as in the present invention. The correction of the moving data 2 is not performed.

  The machining data 1 is commanded to the machining program 1 as the movement of the tool for each block. The movement data 2 includes a command related to the command tool T, a control mode, a tool command path (movement path), a tool axis direction vector (tool posture vector), and a command speed. Here, instead of the tool axis direction vector, the angle of the rotation axis of the machine for determining the tool axis direction vector, Euler angle, roll pitch pitch yaw angle, or the like may be used. More preferably, a normal vector N of the machining surface of the workpiece (workpiece) is commanded.

Here, the control mode is
1) Cutting point control mode 2) Tool tip center point control mode 3) One of the machine position control modes. The cutting point control mode is a mode for controlling the position of the cutting point Pe (the point at which the tool comes into contact with the workpiece) Pe and the feed speed according to the movement data 2. In this mode, the movement data 2 commanded to the machining program 1 is the position of the cutting point Pe and its feed speed, that is, the machining shape and the machining speed itself. The tool tip center point control mode is a mode for controlling the position and feed speed of the tool tip center point Pc according to the movement data 2. In this mode, the movement data 2 commanded to the machining program 1 is the position of the tool tip center point Pc and its feed speed, and the tool tip center point Pc is the tool diameter (d, r) relative to the cutting point Pe. This is the corrected position. Further, in the machine position control mode, the position of the machine position Pm, the position θ of the rotation axis (or the control axis for controlling the posture of the tool) and the feed speed (the combined speed of all axes including the rotation axis) are moved data 2 It is a mode to command according to. In this mode, the movement data 2 commanded to the machining program 1 is the machine position Pm, the rotational axis position θ, and the feed speed. The machine position Pm is in the tool axis direction w by the tool length h with respect to the tool tip center point Pc. The position is corrected in the direction.

  In the cutting point control mode, the shape of the machining to be originally performed can be commanded directly, so that it can be commanded with high accuracy, and the movement data 2 does not depend on the tool dimensions (tool diameter, tool length), so a machining program 1 is created for each tool. There is no need. However, conversely, in the cutting point control mode, the NC adjusts the tool diameter and tool length, so that the tool axial direction (tool axis direction vector w) is oriented perpendicular to the machining surface (tool In a state where the bottom surface is parallel to the machining surface, that is, a singular point (or singular posture), the tool radius correction amount changes discontinuously, leading to overload and deterioration of accuracy. Hereinafter, in the present invention, when the cutting point control mode is commanded to the machining program 1, it is determined whether or not there is a singular point on the movement path. If there is a singular point, the movement data 2 is corrected. A method for suppressing a sudden change in the tool radius correction amount by operating in a non-cutting point control mode (tool tip center point control mode or machine position control mode) in the section near the singular point in the block will be described.

In the cutting point control mode, the movement from the start point to the end point instructed by the machining program 1 is performed using an arbitrary parameter t, the cutting point Pe (t), the unit tool axis direction vector w (t), the machining surface. It is assumed that the unit normal vector N (t) The parameter t is a movement time from the start point or a movement distance from the start point, or a value obtained by normalizing them so that the start point is 0 and the end point is 1. For example, it is assumed that the parameter t is normalized by dividing the movement distance from the start point by the movement distance L from the start point to the end point so that the start point is 0 and the end point is 1. If the position of the cutting point is linearly interpolated between the start point P0 and the end point P1,
Pe (t) = P0 + (P1-P0) t (1.1)
And The tool axis direction vector is rotated at a constant angular velocity around an axis perpendicular to both vectors between the unit tool axis direction vector w0 at the start point and the unit tool axis direction vector w1 at the end point.

w (t) = Rot (nw, φw · t) w0 (1.2)
nw = (w0 × w1) / | w0 × w1 | (1.3)
φw = cos ⁻¹ (w0 · w1) (1.4)

  Here, nw is a unit vector in a direction perpendicular to w0 and w1, and “x” on the right side of the equation (1.3) indicates an outer product of the vectors. Φw is an angle formed by w0 and w1, and “·” on the right side of the equation (1.4) indicates an inner product of the vectors. Rot (k, φ) in equation (1.2) is a rotation matrix for rotating around the vector k by an angle φ. Similarly, the unit normal vector N (t) of the machining surface is rotated between the unit normal vector N0 at the start point and the unit normal vector N1 at the end point at a constant angular velocity around an axis perpendicular to both vectors. .

N (t) = Rot (nn, φn · t) N0 (1.5)
nn = (N0 × N1) / | N0 × N1 | (1.6)
φn = cos ⁻¹ (N0 · N1) (1.7)

  FIG. 6 is a flowchart showing the overall processing flow of the first embodiment of the present invention. In the figure, step ST100 is a process for determining whether or not there is a singular point on the moving route, and is performed by the singular point determination unit 4. If it is determined in step ST100 that there is a singular point, the movement data 2 is corrected in step ST200. Step ST200 is performed by the movement data correction unit 6. Step ST300 is a process of performing interpolation based on the movement data 2 (or the corrected movement data 7), and is performed by the interpolation unit 8. Details of each step will be described below.

Specifically, step ST100 performs processing according to the flowchart shown in FIG. In FIG. 7, in step ST110, it is determined whether or not the machining program 1 has a command for the normal vector N of the machining surface. If there is an N command, the process proceeds to step ST111. In step ST111, when the normal vector N of the machining surface and the tool axis direction vector w are parallel, it is determined that the point is a singular point. When the angle formed by N and w is 0 degree, that is, | N × w | = 0 (1.8)
In the case of, it is judged as a singular point. On the other hand, if there is no normal vector N command in step ST110, the moving direction vector v and the tool axis direction vector w are used using the moving direction vector of the tool (corresponding to the unit vector of the moving direction and the tangent vector of the moving path) v. A vector u perpendicular to the vector is obtained, and a vector perpendicular to u and the moving direction vector v is obtained as a normal vector N.

u = v × w / | v × w | (1.9)
N = u × v / | u × v | (1.10)

Here, the moving direction vector v is a unit vector in the direction in which the cutting point moves, and the tangent vector of the moving path is obtained by differentiating Pe (t) with t as a unit vector. For example, in the case of linear interpolation, from equation (1.1),
v = (P1-P0) / | P1-P0 | (1.11)
It is represented by Alternatively, when the normal vector N is not passed and v and w are vertical, it is determined as a singular point. That is,
v · w = 0 (1.12)
In this case, it may be determined that it is a singular point.

  The procedure of step ST100 is performed for each block with respect to the start point, end point, and halfway point of the block. In the middle of the block, the calculation is performed as follows.

It is assumed that the tool axis direction vector w (t) is given by equation (1.2) and the normal vector N (t) of the machining surface is given by equation (1.5). If there is an N command in step ST110,
| N (t) × w (t) | = 0 (1.13.1)
T corresponding to the singular point is obtained by solving t satisfying the condition analytically or numerically. Similarly, when there is no N command in step ST110,
N (t) · v (t) = 0 (1.13.2)
T corresponding to the singular point is obtained. When there is no solution, there is no singular point in the block, and when there is a solution, it is determined that there is a singular point at a position where the parametric variable corresponds to the solution t = ts. This position is S = Pe (ts).

  As described above, the singular point is determined only when the tool is a square end mill (d> 0) and a radius end mill (dr> 0, where r is a corner radius).

  Next, referring to FIG. 8, the operation of the correction process (step ST200) of the movement data 2 when there is a singular point in FIG. 6 will be described.

  In step ST201, the tool tip center point Pc coincides with the singular point S from the movement data 2 and the tool data 3 commanded to the machining program 1, and the tool axis direction vector becomes the normal vector Ns of the machining surface at the singular point. The correction points Qa and Qb are calculated from the blade edge positions when they match. Qa is the position of the tool cutting point when it is assumed that the tool tip center point is at S, and the relative positional relationship of the tool cutting point with respect to the tool tip point at this position is the same as before reaching the singular point S. It corresponds to. In this figure, Qa is a point advanced from the singular point S by a distance d in the tool traveling direction. Specifically, it is obtained by subtracting only the tool radius correction vector ΔPcompa from the singular point S.

  Qa = S−ΔPcompa (1.14)

  Here, ΔPcompa is a tool radius correction vector at the point immediately before the singular point S or, approximately, the starting point, and when the parameter at that point is ta, the following equations (1.15) to (1.18) Can be obtained by substituting N = N (ta), w = w (ta), and v = v (ta).

ΔPcomp = d · e (1.15)
e = (N− (N · w) w) / | N− (N · w) w | (1.16)
e = ((N × w) × w) / | (N × w) × w | (1.17)
e = ((v × w) × w) / | (v × w) × w | (1.18)

  Here, e is a unit vector from the cutting point toward the tool tip center point, and is calculated by any one of the above formulas (1.16) to (1.18).

  Similarly, Qb is the tool cutting point when it is assumed that the tool tip center point is at S and the relative positional relationship of the tool cutting point with respect to the tool tip point at this position is the same as after the singular point S is exceeded. Corresponds to the position of. In this figure, Qb is a point returned from the singular point S by a distance d in the tool traveling direction. Specifically, it is obtained by subtracting only the tool radius correction vector ΔPcompb from the singular point S.

  Qb = S−ΔPcompb (1.19)

  Here, ΔPcompb is a tool radius correction vector at the point immediately after the singular point S or approximately at the end point, and when the parameter of the point is tb, the above-described equations (1.15) to (1.18) are used. Can be obtained by substituting N = N (tb), w = w (tb), and v = v (tb).

  Next, in step ST202, the tool axis direction vector w and the machining surface normal vector N at the correction points Qa and Qb are calculated from the movement data 2 and the tool data 3 commanded to the machining program 1. First, Qa is calculated.

  In Qa, if the parameter corresponding to the position is ta = ts + d / L, the tool axis direction vector commanded to the machining program 1 is w (ta). The direction vector wa is set as w (ts) = Ns = N (ts). That is, in Qa, the tool axis direction coincides with the singular point. The normal vector of the machining surface at the point Qa has a value instructed to the machining program 1 N (ta), but this is corrected so that the machining surface normal vector N (ts) at the position before passing through the singular point. −δ) (δ> 0) and the vector Na obtained by slightly rotating the machining surface normal vector Ns at the singular point so as to approach the relative positional relationship between the tool axis direction vector w (ts−δ). . For example, as the simplest example, δ = ts, that is, approach the relative positional relationship (rotation angle including the direction of the rotation axis) between the machining surface normal vector N0 and the tool axis direction vector w0 at the start point. , Rotate by a small angle in a plane including N0 and w0. That is, if the minute angle is set to Δφ, the calculation is performed by the following equation.

Na = Rot (na, Δφ) Ns (1.20)
na = (N0 × w0) / | N0 × w0 | (1.21)

  The minute angle Δφ may be obtained by setting the angle in advance as a parameter, or by multiplying the movement angle from the starting point to the singular point by a predetermined ratio. Δφ is a value equal to or smaller than the angle formed by N0 and w0.

  Similarly, also in Qb, the tool axis direction vector wb is made to coincide with the tool axis direction ws = Ns at the singular point S. Further, the normal vector Nb of the machining surface approaches the relative positional relationship between the machining surface normal vector N (ts + δ) (δ> 0) and the tool axis direction vector w (ts + δ) at the position after passing through the singular point. In this way, the machined surface normal vector Ns at the singular point is a vector Nb that is slightly rotated. For example, as the simplest example, δ = (1−ts), that is, a plane including N1 and w1 so as to approach the relative positional relationship between the machining surface normal vector N1 and the tool axis direction vector w1 at the end point. It is rotated by a small angle inside. That is, if the minute angle is set to Δφ, the calculation is performed by the following equation.

Nb = Rot (nb, Δφ) Ns (1.22)
nb = (N1 × w1) / | N1 × w1 | (1.23)

  The minute angle Δφ may be obtained by setting the angle in advance as a parameter, or by multiplying the movement angle from the starting point to the singular point by a predetermined ratio. Δφ is a value equal to or smaller than the angle formed by N1 and w1.

  In the first embodiment, since the tool is moved only by the cutting point command, it is not necessary to calculate the tool tip center point.

  Furthermore, in step ST203, it changes to the movement data 7 which moves in the following order.

Tool axis direction vector Machined surface normal vector Tool tip center point

Start point w0 N0 −
↓ Cutting point control mode correction point Qa Ns Na −
↓ No movement correction point Qb Ns Nb −
↓ Cutting point control mode end point w1 N1 −

("-" Indicates that setting is not required, that is, no reference is made in the interpolation unit)

  That is, the movement data 7 is from the start point to the end point via Qa and Qb, the tool axis direction vector at Qa is wa = Ns, the machining surface normal vector is Na, and the tool axis direction vector at Qb is wb = Ns and the processing surface normal vector are Nb.

  Next, referring to FIG. 6, the operation of the interpolation process (step ST300) will be described.

When the movement data 7 does not pass the singular point, normal interpolation is performed. That is, when the current parameter is tc, the movement distance from the start point to the end point of the block is L, the command speed is F, and the interpolation cycle is dT, the parameter tn at the next interpolation point is tn = tc + F × dt. / L (1.31)
It is represented by By substituting this tn into the equations (1.1), (1.2), and (1.5) respectively, the next cutting point Pe (tn), the unit tool axis direction vector w (tn), machining A normal vector N (tn) of the surface can be calculated. Using these, the tool radius correction vector ΔPcomp (tn) is obtained according to the equations (1.15) to (1.18), and the tool radius correction vector ΔPcomp (tn) is added to the cutting point Pe (tn). The tip center point Pc (tn) is obtained.

  Pc (tn) = Pe (tn) + ΔPcomp (tn) (1.32)

On the other hand, when the movement data 7 passes through the singular point, the correction point Qa is replaced with the end point and interpolation is performed in the same way in the section from the start point of the block to the correction point Qa. That is, in the formula (1.1) to the formula (1.7),
P1 → Qa
w1 → Ns
N1 → Na
To replace L in the formula (1.31) with | P1-P0 | → Qa-P0 |
Is substituted for Pe (tn), w (tn), and N (tn), and Pc (tn) is similarly obtained using these.

When the correction point Qa is reached, the cutting point is switched to the correction point Qb and the machining surface normal vector is changed to Nb. Further, in the section from the correction point Qb to the end point of the block, the correction point Qb is replaced with the start point, and interpolation calculation is performed in the same manner. That is, in the formula (1.1) to the formula (1.7),
P0 → Qb
w0 → Ns
N0 → Nb
To replace L in the expression (1.31) with | P1-P0 | → | P1-Qb |
Is substituted for Pe (tn), w (tn), and N (tn), and Pc (tn) is similarly obtained using these.

Further, an angle θ between the machine position Pm (three orthogonal axes) and the rotation two axes such that the tool center point coincides with Pc and the tool axis direction vector coincides with w is obtained. In general, in a 5-axis machine, depending on the axis configuration of the machine and the geometric positional relationship between the axes,
w = f (θ) (1.33)
Pc = g _θ (Pm) (1.34)
(Relationship of forward kinematics). Therefore, using this inverse function (relationship of inverse kinematics),
θ (tn) = f ⁻¹ (w (tn)) (1.35)
Pm (tn) = g _θ ⁻¹ (Pc (tn)) (1.36)
Thus, the machine position Pm (tn) and the angle θ (tn) of the two rotation axes are obtained and commanded to the position control units 1 to 5 (reference numerals 12 to 16) of the respective axes as position command values 11 for a total of five axes. .

  In addition, after performing acceleration / deceleration processing (acceleration / deceleration after interpolation) for each axis on the obtained interpolation points (Pm (tn) and θ (tn)), position control of each axis is performed as a position command value 11. You may instruct | indicate to parts 1-5 (code | symbol 12-16). Alternatively, pre-interpolation acceleration / deceleration is applied, and F in Equation (1.31) may be the speed after pre-interpolation acceleration / deceleration instead of the command speed. Alternatively, both pre-interpolation acceleration / deceleration and post-interpolation acceleration / deceleration may be used in combination.

  The interpolation unit 8 sends the position of the cutting point as the current position 9 to the display unit 10 during the cutting point control. When passing through a singular point, for example, as shown in (1) and (2) of FIG. 10, the cutting point moves from the starting point P0 to the point Qa, the point Qb, and the end point P1 in terms of control. However, the cutting point that moves in this way returns on the command path on the way, and changes from point Qa to point Qb in an instant, which is difficult for the NC operator to understand. Therefore, in the corrected portion (section where the cutting point exceeds point S to Qa, section where the cutting point extends from Qb to point S), the current position 9 is sent to the display unit 10 as being at the singular point S and displayed. .

Alternatively, instead of the actual cutting point, the movement data 2 before correction may be used to interpolate on the movement path before correction (command path commanded to the machining program 1). At this time, the interpolation speed is adjusted in conjunction with the actual movement of the tool so that P0 at the start point, S when the tool center point is at S, and P1 at the end point. For example, assuming that the travel distance before correction is L, the travel distance after correction is L ′, and the feed speed before correction is F, the travel speed F ′ after correction is
F ′ = F × L ′ / L (1.37)
As shown, the feed rate is adjusted so as to be proportional to the moving distance. The obtained interpolation point on the movement path before correction is set as the current position 9 and is sent to the display unit 10 for display.

  As a result, position display that is natural and easy for the operator to understand is possible.

  An example of operation in the case of following the above procedure will be described with reference to FIGS.

  As an example in FIG. 9 (1), along the command path commanded to the machining program 1, while the cutting point moves from P 0 to P 1, the point S where the tool axis direction vector and the machining surface normal vector coincide with each other. Consider the case of passing through (hereinafter referred to as singular point S). In the figure, ◯ indicates the tool tip center point, and Δ indicates the cutting point. In this example, until reaching the singular point S, the tool 20 is machined with the blade in the traveling direction of the tool 20 while tilting forward with respect to the machining surface 22, and conversely, after passing through the singular point S, the tool 20 is machined. Machining is performed with a blade in the rear direction of the tool 20 while tilting backward with respect to the surface 22.

  At this time, first, as shown in FIG. 9 (2), the tool tip center point coincides with the singular point S, and the tool axis direction vector at that position is parallel to the machining surface normal vector Ns at the singular point S. The correction points Qa and Qb are obtained according to the procedure of step ST201. Further, the machined surface normal vectors Na and Nb at the correction points Qa and Qb are obtained according to the procedure of step ST202. Na and Nb are obtained from the machined surface normal vector Ns at the singular point S so that Na approaches N0 (more precisely, close to the positional relationship between w0 and N0 (forward tilt state)), and Nb The point is slightly shifted so as to be closer to N1 (more precisely, closer to the positional relationship between w1 and N1 (backward tilted state)).

  As shown in FIG. 10 (1), in the first half of the movement (between the starting point P0 and the correction point Qa), the machining surface normal vector at Qa is the relationship between the tool axis direction vector at the starting point and the machining surface normal vector. Therefore, the machining surface normal vector and the tool axis direction vector do not become parallel, and the calculated value of the tool radius correction vector ΔPcomp does not become indefinite. In the vicinity of the singular point S, the tool cutting point (the blade in the direction of travel of the tool) at the position before passing through the singular point S is operated while being roughly held, and the tool tip center point moves to a point that coincides with the point S.

  When this position is reached, as shown in FIG. 10 (2), the cutting point is switched to the correction point Qb and the machining surface normal vector is changed to Nb. In this part, the tool tip center point and the tool direction vector do not change simply by switching the cutting point of interest, so there is no actual tool or machine movement.

  After that, it moves toward the end point P1. This second half (between the correction point Qb and the end point P1) is also corrected so that the machining surface normal vector at Qb approaches the relationship between the tool axis direction vector at the end point and the machining surface normal vector. The normal vector and the tool axis direction vector do not become parallel, and the calculated value of the tool radius correction vector ΔPcomp does not become indefinite. In the vicinity of the singular point S, the tool moves at a position after passing through the singular point S while roughly holding the tool cutting point (blade in the rear direction of the tool), and moves to a point where the cutting point coincides with the end point P1.

  As described above, in the first embodiment, the correction point is obtained with reference to the edge position at the point where the tool tip center point coincides with the singular point, and the tool axis direction vector and the machining surface normal vector become parallel during movement. Since the machined surface normal vector at the correction point was calculated so that the tool radius would not be changed, the tool radius compensation amount would change continuously, so the tool radius compensation vector would not change abruptly. Since there is no stop, the operation is smoothly and stably, and since a rapid correction operation is not performed, there is an effect that high machining accuracy can be maintained without causing unnecessary deterioration of motion accuracy. Further, since the tool does not move steeply with respect to the processing surface, tool damage and excessive tool wear are not caused, and there is an effect that stable processing is possible.

  In the present embodiment, the movement data correction unit is configured such that the rotation angle formed by the tool axis direction vector with respect to the machining surface normal vector at the start point of the section including the singular point is immediately before the start point of the section including the singular point. Correct the machining surface normal vector and / or the tool axis direction vector at the start point of the section including the singular point so that the rotation angle formed by the tool axis direction vector with respect to the machining surface normal vector at So that the rotation angle formed by the tool axis direction vector relative to the machining surface normal vector at the end point of the tool approaches the rotation angle formed by the tool axis direction vector relative to the machining surface normal vector at the point immediately after the end point of the section including the singular point. Since the machining surface normal vector and / or the tool axis direction vector at the end point of the section including the singular point are corrected, Since the rotation angle of the tool axis direction vector with respect to the normal vector of the work surface is corrected so as to continuously change before and after the section near the singular point, the cutting point itself does not change by the correction, and high-precision machining can be realized. .

  In the present embodiment, the movement data correction unit subtracts the tool radius correction vector at the position immediately before the start point of the section including the singular point from the position of the singular point as the start point of the section including the singular point. Since the end point of the section including the singular point is the position obtained by subtracting the tool radius correction vector at the position immediately after the section including the singular point from the position of the singular point, the tool tip in the section near the singular point Since the amount of movement of the center point is 0, useless movement does not occur and processing can be performed in a short time. In particular, since the correction amount does not reverse the movement direction, smooth movement can be performed in a short time, and the movement is easy to understand, so that the operator can easily operate.

  Further, in the present embodiment, the movement data correction unit uses the start point and end point of the section including the singular point as the singular point, and corrects the machining surface normal vector at the start point and end point of the section including the singular point. Therefore, in the section that does not include the singular point, the command path remains as it is, it is not necessary to remake it, and it is simply a form of inserting the movement by the non-cutting point command of the intermediate part, so the processing becomes relatively simple, There is an effect that calculation time is short. In particular, when the tool radius correction vector is not parallel or opposite when entering or exiting a singular point, machining can be performed with high accuracy.

  The invention according to the present embodiment is characterized in that the position of the cutting edge, which is the most important in machining, is moved along the command path, and the problem of singularities is avoided by correcting the machining surface normal vector. Of course, changing the machined surface normal vector also generally changes the position of the cutting point as viewed from the tool, so it does not mean that the machining error is not affected. In the square end mill, the tool edge is sharp when viewed from the side of the tool. Therefore, as in the present invention, the machining surface normal vector is rotated in the plane including the tool center axis (singular point direction) and the machining surface normal vector. In this case, the cutting point itself does not change, so the influence on machining errors can be completely eliminated. Further, in the case of a radius end mill having a small corner radius, the influence on the machining error is limited by correcting the machining surface normal vector. That is, according to the present invention, it is possible to smoothly operate at a singular point while maintaining machining accuracy.

  In the embodiment described above, when the movement amount of the block is short or when the tool diameter is large, the correction point obtained by calculation may not be in the block. In this case, it is possible to cope with the problem by referring to the preceding and following blocks by pre-reading and correcting the tool data across a plurality of blocks.

  In the present embodiment, it is important to correct the relative geometric relationship between the machining surface normal vector and the tool axis direction vector at the singular point so as to approach the state before and after passing through the singular point, It does not depend on the movement path, tool axis direction vector, or machining surface normal vector interpolation method. For example, even if the movement path is circular interpolation, interpolation may be performed based on the circular arc theoretical formula.

  In the determination of the presence / absence of a singular point in formula (1.8) or formula (1.12), it is practically possible to determine with an appropriate determination tolerance in consideration of the calculation error of the computer. Nor.

Embodiment 2. FIG.
[When switching from a backward leaning posture to a forward leaning posture]
9 and 10 of the first embodiment described above, the case where the tool is switched from the forward tilt posture to the rear tilt posture has been described. In the second embodiment, as shown in FIG. 11 (1), a case will be described in which the tool is switched from the backward leaning posture to the forward leaning posture.

  The configuration and operation of the invention are the same as those of the first embodiment. However, there are some differences between the resulting operation and the effects of the invention. Differences will be described below.

  In step ST201 of FIG. 8, correction points Qa and Qb are obtained based on equations (1.14) to (1.19). There is no difference in how to ask. However, looking at the obtained results, as shown in FIG. 11 (2), Qa is a point returned from the singular point S by the distance d in the tool advancing direction, and Qb is advanced from the singular point S by the distance d in the tool advancing direction. It becomes a point. That is, Qa and Qb are reversed compared to FIG. This is because, in the example of FIG. 9 and the example of FIG. 11, the direction of the tool axis direction with respect to the machining surface normal vector is opposite (forward tilt → back tilt in FIG. 9, rear tilt → forward tilt in FIG. 11). It is.

  The machining surface normal vectors Na and Nb are corrected with respect to the correction points Qa and Qb in the same manner as in the first embodiment, and based on this, the movement from the start point to the end point via Qa and Qb is performed. Data 7 is assumed. That is, as shown in FIG. 12 (1), in the first half of the movement (between the start point P0 and the correction point Qa), cutting is performed with the blade in the rear direction of the tool, and the tool tip center point coincides with the point S. Then, the normal vector of the cutting point and the processing surface is switched (does not move), and the first half of the movement (between the correction point Qb and the end point P1) is cut with the blade in the direction of travel of the tool.

The cutting point for displaying the current position is not an actual cutting point, but is interpolated on the movement path before correction (command path commanded to the machining program 1) using the movement data 2 before correction. Ask. At this time, the interpolation speed is adjusted in conjunction with the actual movement of the tool so that P0 at the start point, S when the tool center point is at S, and P1 at the end point. For example, assuming that the travel distance before correction is L, the travel distance after correction is L ′, and the feed speed before correction is F, the travel speed F ′ after correction is
F ′ = F × L ′ / L (1.37)
As shown, the feed rate is adjusted so as to be proportional to the moving distance. The obtained interpolation point on the movement path before correction is set as the current position 9 and is sent to the display unit 10 for display.

  As described above, even when the tool is switched from the backward tilting posture to the forward tilting posture, the same effect can be obtained by the same processing as that of the first embodiment.

  In addition, especially when the tool is switched from the backward tilting posture to the forward tilting posture, the tool radius correction vector ΔPcomp changes from positive to negative before and after passing through the singular point. When moving by linear interpolation, for example, when the angle between the tool axis direction vector and the machined surface normal vector is selected to move by a non-cutting command, the tool goes backward (machining) (In some cases, the movement proceeds in the direction opposite to the direction of movement commanded to program 1). For example, when the length of the section to be linearly interpolated in the non-cutting point control mode is shorter than the tool outer diameter (2d), the amount (2d) by which the tool radius correction vector changes in the negative direction rather than the moving amount of the cutting point to advance. ), The tool advances in the direction opposite to the direction from the start point to the end point. Such movement in the opposite direction causes accuracy degradation and tool chipping due to shocks when reversing the direction, and there is a wasteful movement of re-cutting the part that has been cut once. However, it is difficult to understand the movement, causing a problem such as a collision caused by an operation error.

  On the other hand, in the present invention, since the correction point is obtained based on the position of the cutting edge at the singular point in the first place, it is possible to make a smooth movement in a short time without going backwards, and the movement is easy to understand. The operation of the operator is easy.

Embodiment 3 FIG.
[When making correction points coincide with singular points]
In the first embodiment, the tool tip center point coincides with the singular point S, and the cutting edge position in the state where the posture of the tool is perpendicular to the machining surface is set as the correction point. However, as another method, the correction point is only the singular point S, the machining surface normal vector at the correction point is corrected as in the first embodiment, and linear interpolation is performed between the correction points by a non-cutting point command. Good. This method will be described below.

  The configuration of the invention is the same as that of the first embodiment shown in FIG. The operation follows the flowcharts of FIGS. 6 and 8, but differs from the first embodiment in the specific processing at each step. The differences will be described below.

  In the present embodiment, the correction points Qa and Qb are made to coincide with the singular point S in step ST201 in FIG.

  Next, in step ST202, the tool axis direction vector w, the machining surface normal vector N, and the tool tip center point at the correction points Qa and Qb are calculated. The tool axis direction vector is made to coincide with the tool axis direction vector ws = Ns at the singular point for both the points Qa and Qb. As in the first embodiment, the machining surface normal vector is the machining surface normal vector N (ts−δ) (δ> 0) and the tool axis direction vector w (ts−δ) at the position before passing through the singular point. The machined surface normal vector Ns at the singular point is a vector slightly rotated so as to approach the relative positional relationship with (). The normal vector Nb of the machining surface is close to the relative positional relationship between the machining surface normal vector N (ts + δ) (δ> 0) and the tool axis direction vector w (ts + δ) at the position after passing through the singular point. The processed surface normal vector Ns at the singular point is a vector Nb slightly rotated. Further, the tool tip center points Pca and Pcb at Qa and Qb are obtained by adding the tool radius correction vector ΔPcomp at each position and posture to the positions (Pca and Pcb) of the cutting points. That is, the tool radius correction vector at the point Qa is obtained by substituting N = Na, w = Ns, and v = v (ts) into the equations (1.15) to (1.18). The tool radius correction vector at the point Qb is obtained by substituting N = Nb, w = Ns, and v = v (ts) into the equations (1.15) to (1.18).

  Furthermore, in step ST203, it changes to the movement data 7 which moves in the following order.

Tool axis direction vector Machined surface normal vector Tool tip center point

Start point w0 N0 −
↓ Cutting point control mode correction point Qa Ns Na Pca
↓ Tool tip center control mode correction point Qb Ns Nb Pcb
↓ Cutting point control mode end point w1 N1 −

  That is, the movement data 7 from the start point to the end point via Qa and Qb is set, the tool axis direction vector in Qa is Ns, the machining surface normal vector is Na, and the tool tip center point is Pca. The tool axis direction vector in Qb is Ns, the machining surface normal vector is Nb, and the tool tip center point is Pcb. Of these, the cutting point control mode moves from the start point to Qa and from Qb to the end point. On the other hand, the movement from Qa to Qb is performed in a non-cutting point control mode (for example, a tool tip center point control mode). Since the tool tip center point is interpolated in this section, it is necessary to obtain the tool tip center points Pca and Pcb. In other sections (cutting point control section), the calculation of the tool tip center points Pca and Pcb is not essential.

  In step ST300, when the movement data 7 does not pass through the singular point, the description is omitted because it is the same as that in the first embodiment. Even when the movement data 7 passes through the singular point, the section in which the cutting point control is performed (the section from the start point to the correction point Qa and the section from the correction point Qb to the end point) is the same as in the first embodiment, and thus the description is omitted. To do. Control from the correction point Qa to the correction point Qb is performed not in the cutting point control mode but in the non-cutting point control mode (here, an example of the tool tip center point control mode is shown).

When the cutting point reaches the correction point Qa, the tool tip center point control mode is switched. In the tool tip center point control mode, interpolation control is performed on the tool tip center point. That is, first, assuming that the current parameter is tc, the movement distance from Pca to Pcb is L, the command speed is F, and the interpolation cycle is dT, the parameter tn at the next interpolation point is tn = tc + F × dt / L. (3.1)
It is represented by Using this tn, the interpolation point Pc (tn) of the next tool tip center point is, in the case of linear interpolation,
Pc (tn) = Pca + (Pcb−Pca) tn (3.2)
It is represented by The tool axis direction vector w (tn) is constant in this section (w (tn) = Ns). From the obtained interpolation point Pc (tn) of the tool center point and the tool axis direction vector w (tn), in the same way as in the first embodiment, Pm is used using Equations (1.33) to (1.36). (Tn) and θ (tn) are obtained and set as a position command value 11 and commanded to the position control units 1 to 5 (reference numerals 12 to 16).

  An example of the operation in the case of following the above procedure will be described with reference to FIGS.

  FIG. 13A is the same example as FIG. At this time, first, as shown in FIG. 13 (2), Na is slightly rotated from Ns so as to approach the relationship between N0 and w0 at the starting point. Nb is slightly rotated from Ns so as to approach the relationship between N1 and w1 at the end point. Further, tool tip center points Pca and Pcb are obtained when the cutting point is a singular point S, the tool axis direction vector is Ns, and the normal vector of the machining surface is Na or Nb. Here, the angles at which Na and Nb are rotated from Ns are the same as those in the first embodiment.

  As shown in FIGS. 14 (1) and (3), the first half of the movement (between the start point P0 and the correction point Qa) and the second half (between the correction point Qb and the end point P1) are processed surface normal vectors. The tool axis direction vector does not become parallel and moves in the cutting point control mode. On the other hand, as shown in FIG. 14 (2), the intermediate portion (between the correction point Qa and the correction point Qb) moves in the tool tip center point control mode. In the tool tip center point control mode, tool radius compensation is not performed, the normal vector of the machining surface is not referred to, and the tool tip center point is interpolated within this interval. There is no problem even if it becomes parallel to the vector.

  During the cutting point control mode, in order to avoid the problem of the singular point, while operating within the NC temporarily switching to the tool tip center point control mode near the singular point (intermediate portion) The current position 9 is the position of the singular point S. Alternatively, instead of the actual cutting point, the movement data 2 before correction may be used to interpolate on the movement path before correction (command path commanded to the machining program 1). At this time, P0 at the start point, S when the tool tip center point is at the midpoint of the section where the non-cutting point command is issued (the tool tip center point is the midpoint between Pca and Pcb), and P1 at the end point. As in the first embodiment, the interpolation speed is adjusted in conjunction with the actual movement of the tool. As a result, position display that is natural and easy for the operator to understand is possible.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and further, the command path remains as it is in the cutting point control section, and it is not necessary to remake it. It becomes the form which only inserts the movement by non-cutting point command. In particular, since the command path does not change (the movement distance does not change) in the cutting point control section, there is no need to correct the command speed. Therefore, when implemented in the NC, the processing becomes relatively simple and the calculation time can be shortened.

  In this embodiment, linear interpolation is performed between the tool tip center points in the respective postures before and after the singular point with reference to the point where the cutting point coincides with the singular point. The points just before and the points that exceed the singularity by the tolerance may be used as the correction points Qa and Qb, respectively.

  In the section between correction points, linear interpolation is performed between the tool tip center points Pca and Pcb. However, other interpolation methods may be used, and in particular, Pca so that the tool tip center point matches S at the center of the section. It is also possible to use the first linear interpolation between point S and point S and the second linear interpolation between point S and point Pca. Alternatively, it is preferable to interpolate with a curve (arc or spline curve) that smoothly connects the points Pca, S, and Pcb because the movement becomes smoother.

  Further, although the tool tip center point control mode is set in the section between the correction points, in order to avoid the singular point, the cutting point control mode is not necessary, and the machine position control mode may be particularly used. Particularly in the present embodiment, since the tool posture does not change in the section between the correction points, the movement of the machine position and the movement of the tool tip center point are simply parallel, and even if the tool tip center point is interpolated, Interpolating between the machine positions Pm is equivalent.

  In the present embodiment, the interpolation unit calculates a position interpolated on the movement path commanded to the machining program separately from the actual position of the cutting point, and displays this as the current position on the screen. For example, the corresponding position on the movement path commanded to the machining program is displayed instead of the point on the corrected movement path. It is hard to invite.

  In the present embodiment, in the section including the singular point in the interpolation unit, the position of the singular point on the movement route instructed to the machining program is calculated and displayed on the screen as the current position. Since the corresponding position on the movement path commanded to the machining program is displayed instead of the point on the corrected movement path, it is easy to correspond to the machining program, and it is natural and easy for the operator to understand. Hard to invite. In particular, it can be clearly understood that it is a section passing through a singular point, which is natural and easy for the operator to understand.

Embodiment 4 FIG.
[Correct tool orientation]
In the first to third embodiments, the moving method is such that the tool tip center point coincides with the singular point S, and the tool posture is perpendicular to the machining surface at this point. However, at this time, not one point of the tool blade edge but two points of the blade edge or the entire tool bottom surface may be in contact with the machining surface, which may cause problems such as an increase in cutting load. In this embodiment, a method for solving this problem will be described.

  The configuration of the invention is the same as that of the first embodiment. The operation follows the flowcharts of FIGS. 6 and 8, but differs from the first embodiment in the specific processing at each step. The differences will be described below.

  In step ST201, the correction points Qa and Qb are made to coincide with the singular point S.

  Next, in step ST202, in addition to the tool axis direction vector w and the machining surface normal vector N at the correction points Qa and Qb, the tool tip center points Pca and Pcb at this time are also calculated. First, Qa is calculated.

  In the embodiment of the present invention, the normal vector itself of the machining surface is not corrected. Therefore, the machining surface normal vector at Qa is made to coincide with the machining surface normal vector Ns at the singular point. On the other hand, the tool axis direction vector is corrected in order to avoid that the entire tool bottom surface contacts the machining surface at a singular point. That is, at the singular point S, the value commanded to the machining program 1 is ws = w (ts), but it is corrected and the machining surface normal vector ws at the singular point is slightly changed before passing the singular point. A vector wa rotated so as to approach the tool axis direction vector w (ts−δ) (δ> 0) at the position. For example, the tool axis direction vector w0 at the starting point is rotated from ws by a minute angle Δφ.

wa = Rot (nwa, Δφ) ws (4.1)
nwa = (ws × w0) / | ws × w0 | (4.2)
Here, Δφ is selected as in the first embodiment.

  Further, the tool tip center point Pca at this time is obtained by adding the tool radius correction vector ΔPcomp to the cutting point Qa. Here, ΔPcomp is obtained by substituting N = Ns, w = wa, and v = v (ts) into equations (1.15) to (1.18).

  Similarly, in Qb, the machining surface normal vector at Qb is made to coincide with the machining surface normal vector Ns at the singular point. The tool axis direction vector wb is a vector rotated from the machined surface normal vector ws at the singular point so as to approach the tool axis direction vector w (ts + δ) (δ> 0) at the position after passing through the singular point. And For example, the tool axis direction vector w1 at the end point is rotated from ws by a minute angle Δφ. Here, Δφ is selected as in the first embodiment. Further, the tool tip center point Pcb at this time is obtained by adding the tool radius correction vector ΔPcomp to the cutting point Qb. Here, ΔPcomp is obtained by substituting N = Ns, w = wb, and v = v (ts) into equations (1.16) to (1.19).

  Furthermore, in step ST203, it changes to the movement data 7 which moves in the following order.

Tool axis direction vector Machined surface normal vector Tool tip center point

Start point w0 N0 −
↓ Cutting point control mode correction point Qwa Ns Pca
↓ Tool tip center control mode correction point Qb wb Ns Pcb
↓ Cutting point control mode end point w1 N1 −

  That is, the movement data 7 is from the start point to the end point via Qa and Qb, the tool axis direction vector in Qa is wa, the machining surface normal vector is Ns, and the tool tip center point is Pca. The tool axis direction vector in Qb is wb, the machining surface normal vector is Ns, and the tool tip center point is Pcb. Of these, the cutting point control mode moves from the start point to Qa and from Qb to the end point. On the other hand, the movement from Qa to Qb is performed in a non-cutting point control mode (for example, a tool tip center point control mode). Since the tool tip center point is interpolated in this section, it is necessary to obtain the tool tip center points Pca and Pcb. In other sections (cutting point control section), the calculation of the tool tip center points Pca and Pcb is not essential.

  In step ST300, when the movement data 7 does not pass through the singular point, the description is omitted because it is the same as that in the first embodiment. Even when the movement data 7 passes through the singular point, the section in which the cutting point control is performed (the section from the start point to the correction point Qa and the section from the correction point Qb to the end point) is the same as in the first embodiment, and thus the description is omitted. To do. Control from the correction point Qa to the correction point Qb is performed not in the cutting point control mode but in the non-cutting point control mode (here, an example of the tool tip center point control mode is shown).

When the cutting point reaches the correction point Qa, the tool tip center point control mode is switched. In the tool tip center point control mode, interpolation control is performed on the tool tip center point. The interpolation of the interpolation point Pc (tn) at the tool tip center point is the same as in equations (3.1) and (3.2). Further, for the tool axis direction vector w (tn), in equations (1.2) to (1.4),
w0 → wa
w1 → wb
t → tn
Replace with From the obtained interpolation point Pc (tn) of the tool center point and the tool axis direction vector w (tn), in the same way as in the first embodiment, Pm is used using Equations (1.33) to (1.36). (Tn) and θ (tn) are obtained and set as a position command value 11 and commanded to the position control units 1 to 5 (reference numerals 12 to 16).

  An example of the operation in the case of following the above procedure will be described with reference to FIGS.

  FIG. 15A is the same example as FIG. At this time, first, as shown in FIG. 15 (2), the tool axis direction vector wa is slightly shifted from the normal vector Ns of the machining surface at the singular point so as to approach the tool axis direction vector w0 at the starting point. Further, the tool axis direction vector wb is slightly shifted from the normal vector Ns of the machining surface at the singular point so as to approach the tool axis direction vector w1 at the end point. Further, the tool tip center points Pca and Pcb are obtained when the cutting point is the singular point S and the normal vector of the machining surface is Ns and the tool axis direction vectors are wa and wb, respectively.

  As shown in FIG. 16 (1), in the first half of the movement (between the starting point P0 and the correction point Qa), the tool axis direction vector wa when the cutting point coincides with Qa is from Ns to the starting tool axis direction. Since the correction is made so as to approach, the machining surface normal vector and the tool axis direction vector do not become parallel, and the calculated value of the tool radius correction vector ΔPcomp does not become indefinite.

  When the cutting point reaches Qa, that is, when the tool tip center point reaches Pca, the cutting point control mode is switched to the tool tip center point control mode. In this tool tip center point control mode, the tool radius is not corrected, the normal vector of the machining surface is not referred to, and the tool tip center point is interpolated (FIG. 16 (2)). There is no problem if the direction vector is parallel to the normal vector of the machining surface. When the tool center point reaches the point Pcb, the cutting point control is switched again.

  As shown in FIG. 16 (3), the cutting point control is performed in the latter half of the movement (between the correction point Qb and the end point P1), but the machining surface normal vector and the tool axis direction are the same as in the first half of the movement. The vectors do not become parallel, and the calculated value of the tool radius correction vector ΔPcomp does not become indefinite.

  During the cutting point control mode, in order to avoid the problem of singular points, the current position 9 remains during operation while switching to the tool tip center point control mode temporarily in the vicinity of the singular points inside the NC. The position of the singular point S. Alternatively, instead of the actual cutting point, the movement data 2 before correction may be used to interpolate on the movement path before correction (command path commanded to the machining program 1). At this time, P0 at the start point, S when the tool tip center point is at the midpoint of the section where the non-cutting point command is issued (the tool tip center point is the midpoint between Pca and Pcb), and P1 at the end point. As in the first embodiment, the interpolation speed is adjusted in conjunction with the actual movement of the tool. As a result, position display that is natural and easy for the operator to understand is possible.

  As described above, according to the present embodiment, when focusing on the locus of the moving blade tip, cutting is performed at one place on the bottom surface of the tool in the first half and second half of the movement, and the blade is replaced in the middle portion. Both blades do not touch the machining surface, and a wide area of the tool bottom does not contact the machining surface at the same time. If a wide range of the bottom surface of the tool comes into contact with the machining surface, the cutting resistance increases rapidly and may cause tool damage. However, according to this embodiment, the problem is solved and the cutting edge is always 1 Since the cutting edge does not touch the machined surface at the point where it touches the machined surface or includes a singular point, the wide area of the tool bottom does not contact the machined surface at the same time. Without causing this, stable machining with less risk of tool damage can be realized. In addition, when pick-feed machining is performed, the fact that a wide area on the bottom of the tool is in contact with the machining surface means that the machining is carried out to the adjacent path and interferes with the next machining shape. However, according to the present embodiment, the problem is solved and high-precision machining can be realized.

  In the present embodiment, linear interpolation is performed between the tool center points in the respective postures before and after the singular point with reference to the point where the cutting point coincides with the singular point. An appropriate tolerance is provided in consideration of a CAM calculation error included in the transferred data, and correction points Qa and Qb are points that are just before the tolerance of the singular point and points that exceed the tolerance of the singular point, respectively. preferable.

  Further, as described in the third embodiment, the section between the correction points may be interpolated with a broken line or a curve passing through the singular point S. In addition, the position of the machine position Pm and the position θ of the rotation axis (or the control axis for controlling the posture of the tool) may be interpolated by a straight line or a curve instead of the center point of the tool tip.

  In the present embodiment, the tool axis direction vector is corrected at the correction point. However, in combination with the third embodiment, both the tool axis direction vector and the machining surface normal vector may be corrected at the correction point. . That is, the tool axis direction vector and the machining surface normal vector are not parallel at the correction point, and the tool axis direction vector and the machining surface normal vector are relative to the start point at the correction point Qa and the end point at the correction point Qb. As long as the geometrical relationship is close. Thereby, an intermediate effect between the third embodiment and the fourth embodiment is obtained.

Embodiment 5. FIG.
[When the angle is different]
In the above-described embodiment, an example has been given of the case where the tool is tilted forward to backward, or vice versa. However, there are cases where the singular point is reached in the forward leaning posture, and after exiting from the singular point, the posture is backward leaning, but also in the left-right direction with respect to the traveling direction. In general, depending on the tool axis direction vector before and after the singular point and the machining surface normal vector, the angle formed by the tool radius correction vector before passing the singular point and the tool radius correction vector after passing the singular point may be 0 degrees or 180 degrees. There can be any angle. Since the above-described embodiment constitutes a calculation formula that can be solved for an arbitrary tool radius correction vector and a machined surface normal vector, such a case can be dealt with.

  As an example, FIG. 17 (1) shows a case where the third embodiment is applied, and FIG. 17 (2) shows a case where the fourth embodiment is applied. The figure shows an operation example when the tool is inclined to the right side with respect to the traveling direction after passing through the singular point. In the figure, a circle or an ellipse indicates a tool bottom contour. The point where the horizontal axis and the vertical axis intersect is a singular point. In this figure, the tool bottom contour is projected onto a plane perpendicular to the machining surface normal vector (= tool axis direction vector) at the singular point, and the horizontal axis direction is adjusted to the moving direction. Further, Δ and black triangle indicate cutting points, and ○ indicates the center point of the tool tip. The tool moves in the order of the starting point (i) → (ii) → (iii) → (iV).

  In the case of (1) in the figure, the tool axis direction coincides with the singular point in (ii) (the tool bottom contour is a perfect circle), and the tool tip center point is interpolated from Pca to Pcb in that posture, Go to iii). When (iii) is reached, the cutting point is set to S, and the cutting point is interpolated from S to P1.

  In the case of (2) in the figure, the tool axis direction is slightly shifted from the singular point in (ii) (the tool bottom contour is elliptical), and the tool tip center point is changed from Pca to Pcb while changing the tool posture to the posture of (iii). And interpolate until (iii). When (iii) is reached, the cutting point is set to S, and the cutting point is interpolated from S to P1.

  As described above, according to the present invention, the angle formed by the tool radius correction vector before passing through the singular point and the tool radius correction vector after passing through the singular point is neither 0 degrees nor 180 degrees, and the singular point with respect to an arbitrary angle. Passage is possible. In addition, when the direction of the tool radius correction vector is not parallel to the direction of travel of the tool, it is generally applicable, for example, from the tilt of the tool toward the right to the tilt of the tool relative to the direction of travel of the tool. It can also be applied to passing through singular points.

Embodiment 6 FIG.
[For concave shape]
In particular, when the processing surface is concave, interference (cutting) with the peripheral processing shape becomes a problem.

  As shown in FIG. 18 (1), when the correction points Qa and Qb are obtained in step ST201 in accordance with the above first to third embodiments, the tool tip center point matches the singular point S. If the tool interferes with the surrounding movement path, the tool tip center point should be at a position away from the workpiece in the tool axis direction and away from the workpiece so that the bottom surface of the tool touches the surrounding shape at least at one point. Place. At this position, Qa and Qb are obtained as in step ST201.

  Alternatively, as shown in FIG. 18 (2), when the tool axis direction vectors wa and wb corrected in step ST201 are obtained in accordance with the fourth embodiment, the tool is matched with the singular point S. Is interfered with the surrounding movement path, Δφ, which is normally a very small angle, is set to be larger so that the bottom surface of the tool is in contact with the surrounding shape only at the cutting point so as not to interfere. In this posture, Pca and Pcb are obtained as in step ST202.

  As a result, when passing through a singular point, interference (cutting) with the surrounding machining shape does not occur, and machining accuracy is improved. In particular, when the processed surface is concave, interference is likely to occur.

  As described above, in the present embodiment, in the movement data correction unit, the start point and the end point of the section including the singular point interfere with the movement path of the predetermined distance or the predetermined number of blocks outside the section including the singular point. The tool position is corrected in the direction away from the machining surface in the direction of the tool axis so that it does not cause interference (cutting) with the surrounding machining shape when passing through the singular point. Machining accuracy is improved.

  Furthermore, it is more effective to calculate not only the block having the singular point but also the preceding and following blocks by prefetching and calculating the interference in a wider range.

Embodiment 7 FIG.
[To return]
As shown in FIG. 19A, the tool may temporarily become a singular point from the forward leaning posture and then return to the forward leaning posture again. As described above, the tool radius correction vector ΔPcomp may not change significantly before and after the singular point temporarily. In such a case, when the first, second, and third embodiments are applied, if the relative positional relationship between w0 with respect to N0 and w1 with respect to N1 is substantially the same, as shown in FIG. And Nb are close to each other, and an operation for holding the tool radius correction vector ΔPcomp is performed even at a singular point.

  Similarly, when Embodiment 4 is applied, wa and wb are close to each other, and an operation is performed to hold the tool radius correction vector ΔPcomp even at a singular point.

  In machining, there is a case where the tool is basically desired to be cut only by tilting forward or backward. Even in such a case, depending on the machining shape, the tool may be temporarily perpendicular to the machining surface. In such a case, if the tool radius correction vector is greatly changed at a singular point, especially if the tool radius correction vector is set to 0 at a singular point, the machining shape may be scraped. . For example, in the example of this figure, if the center point of the tool tip coincides with the singular point S, it will be understood that the lower right of the tool interferes with the command path. In this way, in the case of an application where machining is basically performed with a blade in a certain direction as viewed from the tool, it becomes a singular point temporarily as in this embodiment, and the original tool axis direction as viewed from the workpiece. In the case of returning to (without passing through the singular point), it is effective to prevent unnecessary interference by performing an operation of holding the tool radius correction vector ΔPcomp.

  As described above, in this embodiment, when the tool radius correction vector immediately before reaching the singular point and the tool radius correction vector immediately after starting from the singular point are in the same direction in the movement data correction unit, Since the tool radius correction vector is held in the vicinity of the point, unintentional cutting is prevented in the case of machining where the tool is basically tilted with respect to the machining surface in a certain direction.

Embodiment 8 FIG.
[In case of radius end mill]
In the present embodiment, a correction method when a radius end mill is used will be described.

As shown in FIG. 20, the tool radius correction vector ΔPcomp in the radius end mill is ΔPcomp = (dr−e) e + r (N−w) (8.1)
It is represented by Here, the first term on the right side indicates a tool radius correction vector corresponding to the radius of the plane of the bottom surface of the radius end mill, as in the formula (1.15), and when the entire bottom surface is in contact with the machining surface, like the square end mill. The tool radius correction vector is indefinite. On the other hand, the second item on the right side indicates the tool radius correction vector for the corner radius, which is uniquely calculated by the normal vector of the machining surface and the tool axis direction vector, and may be indefinite at the singular point. There is no discontinuity before and after.

  Therefore, in the radius end mill, when the normal vector of the machining surface is corrected as in the first to third embodiments, only the first term on the right side is calculated using the corrected movement data 7. The second term on the right side is calculated using the movement data 2 before correction.

  In the figure, the interpolation unit 8 obtains Pe (tn), w (tn), and N (tn) at the next interpolation point using the corrected movement data 7, and these are obtained from the equation (1.15). By applying the equation (1.18), the first term on the right side of the equation (8.1) is obtained. Further, the interpolation unit 8 uses the uncorrected movement data 2 commanded to the machining program 1 to obtain the machining surface normal vector N ′ (tn) as commanded at the next interpolation point, and this and w Using (tn), the second term on the right side of Equation (8.1) is obtained.

  This makes it possible to calculate the radius correction vector for the corner radius, which can be always accurately calculated without being influenced by the singular point, using the machined surface normal vector as commanded, and at the bottom of the radius end mill. Similar to the square end mill, the tool radius correction vector corresponding to the radius of the plane can be calculated while avoiding the problem of singular points by operating while correcting the movement data. That is, according to the present embodiment, it is possible to obtain an accurate machining result even when passing through a singular point using a radius end mill.

  Even in this case, the current position 9 is obtained by interpolation on the movement path before correction (command path commanded to the machining program 1) using the movement data 2 before correction instead of the actual cutting point. May be. As a result, position display that is natural and easy for the operator to understand is possible.

  In the present embodiment, when machining is performed using a radius end mill tool, a tool radius correction vector corresponding to the radius of the flat portion of the tool bottom surface is obtained when obtaining the tool radius correction amount in the movement path correction unit and the interpolation unit. Is calculated using the corrected tool axis direction vector and the machined surface normal vector, while the tool radius correction vector corresponding to the tool corner radius is calculated using the uncorrected tool axis direction vector and the machined surface normal vector. Since the tool radius correction vector is obtained by calculating and adding both, machining can be performed with high accuracy in machining using a radius end mill tool.

It is a figure which shows the example which processes by the edge of a tool bottom face using a square end mill. It is a figure which shows the example which moves, changing the attitude | position of the tool with respect to a process surface continuously. It is a figure which shows the example which processes using a radius end mill. It is the block diagram which showed the structure of the numerical control apparatus in Embodiment 1 of this invention. It is a figure for demonstrating the tool data in Embodiment 1 of this invention. It is a flowchart which shows the flow of the whole process in Embodiment 1 of this invention. It is a flowchart which shows the singularity determination process in Embodiment 1 of this invention. It is a flowchart which shows the correction process of the movement data in Embodiment 1 of this invention. It is a figure which shows the movement data before and behind correction | amendment in Embodiment 1 of this invention. It is a figure which shows the example of operation | movement in Embodiment 1 of this invention. It is a figure which shows the movement data before and behind correction | amendment in Embodiment 2 of this invention. It is a figure which shows the example of operation | movement in Embodiment 2 of this invention. It is a figure which shows the movement data before and behind correction | amendment in Embodiment 3 of this invention. It is a figure which shows the example of operation | movement in Embodiment 3 of this invention. It is a figure which shows the movement data before and behind correction | amendment in Embodiment 4 of this invention. It is a figure which shows the example of operation | movement in Embodiment 4 of this invention. It is a figure which shows the example of operation | movement in Embodiment 5 of this invention. It is a figure which shows the movement data after correction | amendment in Embodiment 6 of this invention. It is a figure which shows the movement data before and behind correction | amendment in Embodiment 7 of this invention. It is a figure explaining the tool diameter correction vector in Embodiment 8 of this invention.

Explanation of symbols

  1 machining program, 2 movement data commanded to machining program, 3 tool data, 4 singularity determination unit, 5 singularity determination result, 6 movement data correction unit, 7 corrected movement data, 8 interpolation unit, 9 current position DESCRIPTION OF SYMBOLS 10 Display part, 11 Position command value, 12 Position control part 1, 13 Position control part 2, 14 Position control part 3, 15 Position control part 4, 16 Position control part 5, Pe cutting point, Pc Tool tip center point, w Tool axis direction vector, N Machining surface normal vector, Q correction point, S singular point, ΔPcomp Tool radius correction vector.

Claims (10)

Use a square end mill tool or a radius end mill tool to drive the machine so that the cutting point where the bottom of the tool touches the workpiece moves along the movement path specified in the machining program while changing the tool posture with respect to the workpiece. A numerical control device for controlling an axis,
Based on the movement data commanded to the machining program and the tool data of the tool to be used, it is determined whether there is a singular point where the tool axis direction is perpendicular to the machining surface of the workpiece during the movement of the tool A singularity determination unit,
When the singular point determination unit determines that there is a singular point during movement, the movement data correction unit that divides the movement data into a movement section including a singular point and a movement section not including a singular point;
Of the movement sections divided by the movement data correction unit, in the movement section including the singular point, if there is movement, the position of the tool tip center point is obtained by interpolation, while the singular point is not included. In the movement section, the tool tip center point is obtained by interpolating the position of the cutting point, obtaining the tool surface normal vector and the tool radius correction vector from the tool axis direction to the tool tip center point, and adding them. An interpolation unit that obtains the position of each axis of the machine using an inverse kinematics function from the tip center point;
And a position control unit that controls a drive shaft of the machine according to the position of each axis of the machine determined by the interpolation unit. The movement data correction unit
The rotation angle made by the tool axis direction vector with respect to the machining surface normal vector at the start point of the section including the singular point is
To approach the rotation angle formed by the tool axis direction vector with respect to the machining surface normal vector at the point immediately before the start point of the section including the singular point,
Correct the machining surface normal vector and / or the tool axis direction vector at the start point of the section including the singular point,
The rotation angle formed by the tool axis direction vector with respect to the machining surface normal vector at the end point of the section including the singular point,
To approach the rotation angle formed by the tool axis direction vector with respect to the machining surface normal vector at the point immediately after the end point of the section including the singular point,
The numerical controller according to claim 1, wherein a machining surface normal vector and / or a tool axis direction vector at an end point of a section including the singular point is corrected. The movement data correction unit
The starting point of the section including the singular point is a position obtained by subtracting the tool radius correction vector at the position immediately before the starting point of the section including the singular point from the position of the singular point,
3. The numerical value according to claim 1, wherein the end point of the section including the singular point is a position obtained by subtracting a tool radius correction vector at a position immediately after the section including the singular point from the position of the singular point. Control device. The movement data correction unit
The starting point and ending point of the section including the singular point are singular points,
The numerical control apparatus according to claim 1, wherein a machining surface normal vector at a start point and an end point of a section including the singular point is corrected. The movement data correction unit
The starting point and ending point of the section including the singular point are singular points,
The numerical control device according to claim 1, wherein a tool axis direction vector at a start point and an end point of a section including the singular point is corrected. The movement data correction unit
The starting point and the ending point of the section including the singular point are positioned in the direction away from the machining surface in the tool axis direction so as not to interfere with a predetermined distance or a predetermined number of blocks outside the section including the singular point. It correct | amends. The numerical control apparatus of any one of Claim 1 thru | or 5 characterized by the above-mentioned. The movement data correction unit
When the tool radius correction vector immediately before reaching the singular point and the tool radius correction vector immediately after starting from the singular point are in the same direction, the tool radius correction vector is held in the vicinity of the singular point. The numerical control apparatus according to any one of claims 1 to 6. The interpolation unit
Apart from the actual cutting point position,
The numerical control apparatus according to claim 1, wherein a position interpolated on a movement route commanded by the machining program is calculated and displayed on the screen as a current position. The interpolation unit
In the section including a singular point, the position of a singular point on the movement route commanded by the machining program is calculated, and this is displayed on the screen as the current position. The numerical controller described. When processing using a radius end mill tool as the tool,
When the movement path correction unit and the interpolation unit obtain the tool radius correction amount,
The tool radius correction vector corresponding to the radius of the flat part on the bottom of the tool is calculated using the corrected tool axis direction vector and the machined surface normal vector,
On the other hand, the tool radius correction vector corresponding to the tool corner radius is calculated using the tool axis direction vector and the machining surface normal vector before correction,
The numerical controller according to any one of claims 1 to 9, wherein the tool radius correction vector is obtained by adding both.

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