JP3511583B2 - Numerical control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a numerical control method for controlling the speed of a processing tool of a machine tool based on a command path and a command feed speed commanded by a machining program, and particularly when the command path includes an error. Also relates to a method of a numerical control device capable of performing processing in a short time without causing scratches on the processed surface.

[0002]

2. Description of the Related Art In a numerically controlled machine tool, machining processing is performed by designating a command path and a feed rate by a machining program that is input. FIG. 16 is an enlarged view of a part of the command path represented by the machining program. In FIG. 16, the solid line is the original route, and a to c are
It represents one section when the original route is defined by a minute straight line and a minute arc, respectively. Since the original route is often difficult to solve mathematically, it is defined as a set of minute straight lines, arcs, spline curves, and NURBS curves.

One section of the command path thus defined is described for each block in the machining program. In each block, in addition to the command path approximated for each section, information necessary for machining such as command feed speed is described, and tens of thousands of blocks are described in the machining program. The numerical control device interpolates the command path at a predetermined sampling cycle based on the block information described in the machining program, and performs acceleration / deceleration control of the machine tool.

Next, the operation of the numerical controller will be described. FIG. 17 is a block diagram showing the configuration of a general numerical controller. First, the program reading unit 1 interprets a machining program and reads it as internal data D _t . Next, the block information creation unit 2 calculates, based on the data for each block included in this internal data D _t , data necessary for coordinate system processing, interpolation of a command path such as block length and tangent vector, and shape. Preprocessing such as calculation of the permissible speed is performed to create block information B _D related to the route and command feed speed. The acceleration / deceleration / interpolation unit 3 performs acceleration / deceleration and interpolation based on the block information B _D , and sends a command position, a command speed, a command current, etc. to the servo control unit 4.

As described above, the machining program describes the data necessary for machining such as the command path and the feed rate. However, since the machine and the servo system have a follow-up delay, the machining tool deviates from this command path. As a result, a locus error or mechanical vibration may occur. Such locus errors are particularly noticeable at locations where the moving direction changes greatly, such as small-diameter circular arcs and corners, and the locus errors and mechanical vibrations increase as the feed speed moving along the path increases.

The numerical control device deals with these problems by decelerating at a portion where the moving direction changes abruptly such as an arc or a corner portion. Regarding the deceleration at the arc portion or the corner portion, there is a method of adjusting the feed rate according to the angle formed by the blocks forming the arc portion or the corner portion with the adjacent blocks. According to Japanese Patent Laid-Open No. 02-137006,
When the angle formed by the adjacent blocks is θ, the feed rate F is given by the following formula.

[0007]

[Equation 1]

In Equation 1, a _max is an allowable acceleration, k is an accuracy coefficient, and δt is a sampling cycle.

[0009]

Generally, in die machining, a machining shape is designed by a three-dimensional model (CAD process),
A machining program for machining this three-dimensional shape is created (CAM process). However, when the machining program is created from the three-dimensional model in the CAM process, an error occurs in the command path. The effect of this command path error on machining will be described below.

FIG. 18A shows a command path which is located adjacent to a certain smooth machined surface. In FIG. 18A, A is an ideal command path that does not include an error and is output as an original smooth curve. B is a case where an S-shaped command path error occurs in the command path, and C is a case where a stepped command path error occurs.

Generally, in a numerical controller, acceleration / deceleration is performed according to an angle θ formed by adjacent blocks. A ', B', and C'show loci of the work tools when acceleration and deceleration are performed by the angle θ formed between the blocks. Since the deceleration hardly occurs in the command path A having a small angle between blocks, a predetermined trajectory error ε _A corresponding to the command feed speed is generated. On the other hand, in the command path B, the angle θ becomes smaller in the S-shaped portion, so that the speed is decelerated more than in the command path A, and the trajectory error ε _B becomes slightly smaller than the path A. Also, command path C
Then, since the speed is reduced to almost 0 at the step, the trajectory error ε _C becomes almost 0.

In this way, the machine paths B and C approach the command path including the error due to the deceleration caused by the command path error. As a result, only the parts of the machine loci B and C look like scratches, which causes a problem in terms of the quality of the machined surface. In this case, since the original path is smooth, the command paths B and C must be machined at the same feed rate as A. In addition, since unnecessary deceleration occurs in the command paths B and C,
Processing time is unnecessarily extended.

When an error is included in the command path as shown in FIG. 18A, a method of removing the error included in the path (Japanese Patent Laid-Open Nos. 01-098001 and 10-240328) and more precise Fit an arc to (Japanese Patent Laid-Open No. 01-036308)
Therefore, a method of restoring the original route has been proposed. However, these methods are methods in which the original route is estimated from the route including the error, and it is impossible to completely restore the original route.
In the die machining, if the acceleration / deceleration control is incorrect even at one place, the machining surface will be damaged and the product quality will be poor.

Another conventional method is disclosed in Japanese Patent Laid-Open No. 58-3.
As shown in Japanese Patent No. 5607 and Japanese Patent Laid-Open No. 02-66604,
There is a method of estimating the trajectory of the processing tool from the path and the feed speed instructed by the machining program, and controlling so that the trajectory error between the command path and the expected trajectory is equal to or less than the allowable value. However, also in the conventional methods based on these trajectory errors, when the command path includes an error, the corrected command path is directly affected by the error included in the command path.

FIG. 18B shows an example of command paths containing an error and a predicted trajectory predicted from these command paths. In the figure, A ″, B ″, C ″ are command paths A, respectively.
It is a prediction trajectory corresponding to B and C. On the smooth path A, the trajectory error is almost constant at any place, but on the other hand, for the paths B and C containing the error, the trajectory error (ε _A ', ε _B ', ε _C ') is local. Depends on In this way, when the command path includes an error, the trajectory error is directly influenced by the error included in the path. Therefore, when acceleration / deceleration is performed based on the trajectory error, the feed speed varies for each path.

When an error is included in the commanded path as described above, in order to prevent the machining surface from being scratched by the conventional method, the feed rate is lowered to perform the entire machining slowly, or the allowable acceleration or Since the accuracy coefficient was lowered and the speed was changed so that the speed was reduced, the processing speed was unnecessarily reduced. The present invention has been made to solve the above problems, and a numerical controller capable of performing machining in a short time without causing scratches on the machining surface even if the command path includes an error. The purpose is to get.

[0017]

In order to achieve the above-mentioned object, a numerical control device according to the present invention is a machining tool when a speed control of a machine tool is performed by a command path and a command feed speed commanded by a machining program. look at the trajectory from the command position
Prediction based on the transfer characteristics up to the processing position, which is the position of the processing tool at the time, and acceleration of the processing tool on the predicted trajectory
Degree, normal component of acceleration, jerk, or position / velocity / jerk
Calculated Mel the allowable feed rate based feature value representing the vibration component of the velocity or jerk and its tolerance. The transfer characteristic used to predict the locus is obtained by considering at least one of the mechanical characteristic of the machine tool, the characteristic of the servo system, and the acceleration / deceleration characteristic.

Further, it can be obtained by calculating a predicted machining shape of the three-dimensional model from the predicted trajectory and comparing the predicted machining shape with a target machining shape which is set in advance or calculated based on the block information. Calculate the allowable feed rate from the machining error and its allowable value.

Furthermore, by predicting the locus of the processing tool when the speed control of the machine tool is performed by the permissible feed rate obtained according to the above means, and calculating the permissible feed rate from the predicted locus according to the above procedure. , The permissible feed rate at which the characteristic amount is equal to or close to the permissible value is obtained.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. Incidentally, the same or corresponding parts as those of the above-mentioned conventional example are designated by the same reference numerals and the description thereof will be omitted.

Embodiment 1. 1 is a block diagram showing a configuration of a numerical control device according to a first embodiment of the present invention, and FIG. 2 is a flowchart showing the operation thereof. Figure 1
In FIG. 5, reference numeral 5 is a temporary command position creation unit, which has a prefetch buffer 5a for storing block information. Reference numeral 6 denotes a locus predicting unit, which calculates a predicted locus based on the transfer characteristic from the command position to the machining position in consideration of delay of the servo system.

The operation of the numerical controller according to the present embodiment will be described with reference to FIGS. First, the program reading unit 1 interprets a machining program and reads it as internal data D _t . Next, the block information creation unit 2 determines, based on the data for each block included in the internal data, coordinate system processing, calculation of block length and tangent vector, data processing necessary for interpolation of the command path, and shape. Preprocessing such as calculation of the permissible speed is performed to create block information B _D related to the route and command feed speed. Block information B _D created is stored in the look-ahead buffer 5a (ST _{1 1).}

Next, in the temporary command position creating section 5, ST ₁
The block information B _D created in 1 is preread, the command path is read based on the preread block information, and the tentative command position P _o (i) (i is obtained by interpolating the command path at predetermined intervals. = 1,2, ... n) is created (ST ₁ 2). Here, the predetermined distance step is a preset value or a value F _o δt obtained by multiplying the command feed speed F _o by the sampling period δt.
And

After that, the trajectory predicting section 6 uses the temporary command position P _o (i) created in ST ₁₂ to transmit from the command position to the machining position in consideration of the delay of the servo system, the characteristics of the motor and the like. Simulation is performed based on the function, and the predicted trajectory P
(i) calculating a (ST ₁ 3). FIG. 3 shows the temporary command position P _o (i) created by interpolating the command path represented by the solid line and the predicted trajectory P (i) calculated by simulation from the created temporary command position P _o (i).

The transfer function used for trajectory prediction is represented by a continuous-time system or a discrete-time system. However, when performing a simulation on a computer, it is more convenient to use the transfer function of the discrete-time system for performing arithmetic processing. good. An example of the transfer function H (z) of the discrete time system is shown below.

[0026]

[Equation 2]

Here, z is a Z transformer, m is the order of the transfer function, a _j and b _j (j = 0 to m) are coefficients of the numerator polynomial N (z) and the denominator polynomial D (z) of the transfer function, respectively. And is determined by the transfer characteristic from the command position to the machining position that the actual system has.

Next, in ST ₁₃ , the predicted trajectory P (i) calculated
From the above, the feature amount representing the temporal change of the position on the predicted trajectory P (i) of the processing tool is calculated. Here, a normal component An (i) (hereinafter referred to as normal acceleration) of acceleration of the work tool moving on the predicted trajectory P (i) is calculated as this feature amount (ST.
₁₄ ). Let P (k) be the predicted trajectory at i = k, and P (k)
The normal acceleration An (k) at is expressed by the following equation.

[0029]

[Equation 3]

In the above equation, A (k), V (k) and u (k) are the acceleration vector, the direction vector and the unit direction vector at the position P (k), respectively. The acceleration A is shown in FIG.
4 (b) is a vector diagram showing a method of calculating the normal acceleration An (k). Finally, the allowable feed speed Fd is calculated from the normal acceleration An (k) calculated in ST ₁₄ and the preset allowable normal acceleration A _max . The allowable feed speed Fd is given by the following formula.

[0031]

[Equation 4]

Here, Fr is an allowable feed speed when the path can be regarded as a circular arc, Fc is an allowable feed speed when the path can be regarded as a corner, and F _o is a command feed corresponding to the distance step used in ST ₁₂ It's speed. ρ is a value indicating the degree to which the route is close to an arc, and for example, the normal acceleration An (k +) at a position that is forward or backward by a predetermined time h with respect to the magnitude An (k) of the normal acceleration at the position P (k). Calculate using the ratio of h) and An (kh).

[0033]

[Equation 5]

Here, max (An (k + h), An (kh)) is max (An (k + h), An (k) when An (k + h)> An (kh).
-h)) = An (k + h). When A (k) is the acceleration at the corner, the acceleration at the corner is sufficiently larger than the acceleration at the periphery, so max (An (k +
h), An (kh)) / An (k) approaches 0. When A (k) is the acceleration in the arc portion, the acceleration in the arc portion is uniform in the periphery, so An (k + h), An (kh), An (k)
Are almost equal in size, and max (An (k + h), An (k
-h)) / An (k) approaches 1. Also, g (x) is g (0) = 0, g
It is a function that satisfies (1) = 1, and the following equation is used, for example.

[0035]

[Equation 6]

However, when x> 1 in the above equation, g (x) = 1.

The feed rate Fd thus obtained is sent to the acceleration / deceleration / interpolation unit 3 together with the block data. The acceleration / deceleration / interpolation unit 3 performs acceleration / deceleration and interpolation based on the allowable feed speed Fd to create a command position P _o (i) ′ and sends it to the servo control unit. As described in the description of the prior art, there are cases where a command speed, a command current, etc. are sent to the servo control unit in addition to the command position. Can also be used for

FIGS. 5 (a) and 5 (b) show a processing tool obtained by performing acceleration / deceleration based on a trajectory error (hereinafter, conventional method A) and acceleration / deceleration based on an angle (hereinafter, conventional method B) in this method. The loci are obtained by simulation. 5A shows the result when the command path does not include an error, and FIG. 5B shows the result when the command path includes the error. In FIGS. 5A and 5B, a solid line indicates a command path, + indicates a predicted tool trajectory obtained in this method and conventional method A, and ◯, Δ, and X indicate this method and conventional method A, respectively.
It is an actual trajectory when the conventional method B is used. In the conventional method A, the trajectory error was controlled to be 0.006 mm or less.

According to the simulation result shown in FIG. 5A, when the command path does not include an error, the conventional method B is used.
The actual trajectory x due to is equal to the predicted trajectory ◇ according to the present method and the conventional method B, and is largely deviated from the command route. On the other hand, the actual trajectories ◯ and Δ according to this method and the conventional method B are almost the same.

In the simulation result shown in FIG. 5B, the command path includes a stepped error in the S portion.
When processing such a stepped portion, the actual trajectory becomes dull due to a delay in tracking the servo or the like. Since the tracking delay of the servo system is taken into consideration in the transfer function used in the simulation when the predicted trajectory is calculated, no step appears on the predicted trajectory (⋄). Therefore, the shape of the predicted trajectory approaches the original command path that does not include an error. In this case, when the conventional method B is used (x), deceleration occurs at the step portion, so that the trajectory becomes more faithful to the command path. Further, the trajectory (Δ) according to the conventional method A also approaches the command path including the error because the error with the command path is controlled so as to be within the allowable value.

On the other hand, since the present method calculates the allowable feed rate based on the normal acceleration obtained from the predicted locus (⋄), it is hardly affected by the stepped error included in the command path as a result. Further, comparing FIGS. 5A and 5B,
The actual trajectories x and Δ according to the conventional methods A and B are largely different when the command path includes an error and when the command path does not include an error, but are substantially the same in the present method.

As described above, according to the present embodiment, the allowable feed rate is calculated based on the predicted value of the normal acceleration of the processing tool obtained from the predicted trajectory, which affects the error included in the command path. Without being performed, the allowable feeding speed required for the processing tool to move along the original path can be accurately obtained, and unnecessary deceleration at the time of processing can be avoided, so that the processing time can be shortened. Further, even when the command path includes an error, the error is uniform between the adjacent paths, so that a faithful machined surface as designed can be obtained.

In the above description, the permissible feed rate is obtained by using the normal acceleration as the feature amount representing the temporal change of the processing tool position obtained from the predicted trajectory, but the permissible feed rate is also obtained by another feature amount. You can For example, even if the acceleration A (k) instead of the normal acceleration An (k) and the jerk that is a change with time of the acceleration are used as the above-mentioned characteristic amount, it is possible to obtain an allowable feed speed that is not affected by the command path error.

When it is desired to reduce striped scratches generated on a machined surface by a machine that is susceptible to vibration, the vibration component of the machining tool position, velocity, acceleration, or jerk is used as a characteristic amount, and each allowable value is set. The allowable feed rate may be calculated based on

Alternatively, each point P (i) (i = 1,2,
The same effect can be obtained by calculating the feed rate by the equation 1 using the angle θ formed by the line segment connecting the ... N) and the adjacent line segment. By properly using the above feature amounts, it is possible to calculate the allowable feed rate corresponding to the characteristics of the machine tool and the required accuracy of the machined surface.

Further, in the equation 4-1, the feed speed is obtained by internally dividing Fr and Fc according to the value of ρ, but if it is an equation that becomes Fr at the arc portion and Fc at the corner portion, another formula is obtained. It can be a formula. Similarly, in Equation 6, another function (for example, g (x) =-(x-1) ² +1) may be used as long as g (0) = 0 and g (1) = 1 are satisfied. As for the method of obtaining ρ in 5, another function may be used as long as it is 1 at the arc portion and 0 at the corner portion.

Embodiment 2. In the first embodiment, the transfer function shown in Expression 2 is stored in the trajectory prediction unit,
The coefficient was given in advance so as to match the transfer characteristic from the command position to the machining position. The coefficient of the transfer function is determined in consideration of the characteristics of the acceleration / deceleration, the servo system and the machine, but this work is laborious. The present embodiment provides means for automatically setting the coefficient of the transfer function used for calculating the predicted trajectory.

FIG. 6 is a block diagram showing the configuration of a numerical controller according to the second embodiment of the present invention. In FIG.
Reference numeral 8 denotes a transfer function automatic setting unit, and the other components are the same as those in FIG. The operation of the transfer function automatic setting unit 8 will be described with reference to FIG.

The transfer function automatic setting unit 8 includes an acceleration / deceleration parameter Kt such as an acceleration / deceleration time constant T from the acceleration / deceleration / interpolation unit 3,
The servo control unit 4 also inputs servo parameters Ks such as a position loop gain Kp, and mechanical characteristic parameters Km such as a resonance angular frequency ω and a damping ratio ζ by manual operation of an external measuring device or an operator (not shown).

With each of these parameters, the transfer function G ₁ (s) relating to acceleration / deceleration and the transfer function G relating to servo control are given.
₂ (s), a transfer characteristic G ₃ (s) relating to mechanical characteristics is generated.
These transfer functions are expressed by the following equations. Here, s is a parameter in the Laplace transform.

[0051]

[Equation 7]

By taking the product of these, the transfer function G
(s) is expressed by the following equation.

[0053]

[Equation 8]

Next, the continuous-time system function G (s) is converted into the discrete-time system function H (z). Generally, H (z) is given in the form of Equation 2 above. in this case. The coefficients a _j and b _j in Equations 2-1 and 2-2 can be obtained by a known method such as bilinear transformation. Each coefficient a _j calculated by the above method,
b _j is input to the trajectory prediction unit 6 and the transfer function is set.

As described above, according to the second embodiment,
Since the transfer function can be automatically set by inputting the acceleration / deceleration parameter Kt, the servo parameter Ks, and the mechanical characteristic parameter Km to the transfer function automatic setting unit, even if these parameters are changed, it is not necessary to set them again. It is also possible to avoid input mistakes and calculation mistakes when inputting by work.

In the above description, all the transmission characteristics related to acceleration / deceleration, servo control and mechanical characteristics are taken into consideration, but any one which can be ignored may be omitted. For example, when pre-interpolation acceleration / deceleration is performed, the deviation of the path due to acceleration / deceleration does not occur, so the transfer characteristic G ₁ (s) relating to acceleration / deceleration can be omitted. Further, when the delay in the servo system can be almost ignored by the feedforward control, the transfer characteristic G ₂ (s) related to the servo control may be omitted. Further, when the rigidity of the machine is high, the transfer characteristic G ₃ (s) related to the mechanical characteristics may be omitted. As described above, the processing can be simplified by considering only the required transfer characteristic.

Third Embodiment In the first embodiment,
Temporary command position P obtained by interpolating the command path in increments of a predetermined distance _o(i)
The normal acceleration An (i) is calculated from the predicted trajectory P (i) calculated from
The normal acceleration An (i) obtained in this way
Is the allowable normal acceleration A_maxOver, or less than necessary
Allowable normal acceleration A_maxMay have a smaller value
It To maintain accuracy and process in a short time, add normal
Speed A (i) is the allowable normal acceleration A_maxIs almost equal to
It is desirable to process at the feed rate.

In the present embodiment, the provisional command position is created with a step width of a value obtained by multiplying the allowable feed rate Fd calculated by the method described in the first embodiment by the sampling cycle δt, and the trajectory normal acceleration and the allowable value are set. By providing the calculation of the feed speed, a means is provided for obtaining the allowable feed speed at which the normal acceleration An (i) becomes a value closer to the allowable normal acceleration A _max .

FIG. 7 is a block diagram showing the configuration of a numerical control device according to the third embodiment of the present invention, and FIG. 8 is a flowchart showing the operation of this numerical control system. First, S
ST ₁ 1 shown in Embodiment 1 in T ₃ 1 to ST ₃ 4
According ~ST ₁ 4 and the same procedure, the provisional command position P _o1 (i), the estimated track P ₁ (i), the normal acceleration An ₁ (i) and the permissible feed speed Fd ₁ is obtained. Next, the absolute value of the difference between the allowable normal acceleration A _max The normal acceleration An ₁ (i) In ST ₃ 5 | A
_max -An ₁ (i) | is determined whether it is within a predetermined value alpha, the case is within a predetermined value alpha allowable feedrate Fd ₁ obtained in ST ₃ 4 is input to the deceleration-interpolation section 3 It

If the above conditions are not satisfied (| A _max
-An ₁ (i) |> α), the allowable feed speed Fd ₁ obtained in ST ₃ 4 is input to the temporary command position creation unit 5, and the value Fd ₁ δt obtained by multiplying this by the sampling cycle δt is used as the distance. The temporary command position is created again as a step. In this way, the predicted trajectory P ₂ (i) is calculated from the newly created temporary command position, and the normal acceleration An ₂ (i) is obtained again. ST ₃ 2~ST ₃ 5
The process termination condition _{| A ma x -An m (i} ) | ≦ α (m = 1,2, ...
Iterate until n) is satisfied.

[0061] As described above, according to this embodiment, the normal acceleration An _m (i) and the allowable normal acceleration A until the difference _max is equal to or less than a predetermined value created provisional command position ST ₃ 2, predicted trajectory calculated ST ₃ 3, the calculation of the normal acceleration and allowable feedrate ST ₃ 4
Is repeated. As a result, the calculated normal acceleration A
Since n _m (i) has a value very close to the allowable normal acceleration A _max , a highly accurate machined surface can be obtained in a short time.

In the above description, the condition that the absolute value of the difference between the feature value obtained from the predicted locus and the permissible value thereof is equal to or less than the predetermined set value is the end condition for the normal acceleration calculation. Exceeds a predetermined number of times, the absolute value of the difference between the previously obtained permissible feed speed and the two-previously obtained permissible feed speed is less than or equal to a predetermined set value, or these AN
A combination of D and OR may be used as the end condition. Further, by providing the automatic transfer characteristic setting unit described in the second embodiment inside the numerical controller, the automatic transfer characteristic can be set.

Fourth Embodiment In the description of the prior art,
C that converts the machining shape of the 3D model into a machining program
It has been described that an error occurs in the command path in the AM process. In the present embodiment, the predicted machining shape of the three-dimensional model is calculated from the predicted trajectory P (i), and the predicted machining shape is compared with the target machining shape of the three-dimensional model that does not include the error generated in the CAM process. A method for obtaining an allowable feed rate based on the machining error and its allowable value is provided.

FIG. 9 is a block diagram showing the configuration of the numerical controller according to the present embodiment. In FIG. 9, 9 is a machining shape prediction unit, and 10 is a machining error calculation unit. The machining shape predicting unit 9 stores the material shape and the tool shape. Here, the material shape and the tool shape are represented as a three-dimensional model. Further, the processing error calculation unit 10 stores the target processing shape. Other components are the same as those in FIG.

The operation of the numerical controller according to the present embodiment will be described with reference to the flowchart shown in FIG. ST ₁ is first shown in ST ₄ 1~ST ₄ 3 to the first embodiment
The predicted trajectory P (i) is calculated in the same procedure as in _{1 to} ST ₁₃
It is input to the machining shape prediction unit 9. Processing shape prediction unit 9 based on the predicted trajectory P (i), and calculates the three-dimensional prediction machining shape Sld from the material shape and the tool shape is previously set (ST ₄ 4). A known method such as the Z buffer method is used for the simulation for obtaining the three-dimensional predicted machining shape Sld from the predicted trajectory P (i).

Next, in the processing error calculation unit 10, ST ₄
The machining error ε (i) is calculated from the difference between the predicted machining shape Sld obtained in 4 and the target machining shape given in advance.
Here, since the predicted machining shape Sld and the target machining shape are represented by a three-dimensional shape, the machining error ε (i) is calculated as the difference between the surfaces. Further, since the target machining shape does not include an error, it is not affected by the error included in the command path, which is a problem when performing acceleration / deceleration based on the trajectory error.

Next, the permissible feed rate calculation unit 7 calculates the permissible feed rate Fd 'using the machining shape error ε (i). The allowable feed rate Fd 'at the position P (k) is the position P
It can be calculated by the following equation using the processing error ε (k) in (k).

[0068]

[Equation 9]

[0069] Here, Fr 'is permissible feed speed when regarded path an arc, also Fc' is permissible feed speed when regarded as corner path, F _o corresponds to increment distance used in ST ₄ 1 The feed rate. Further, ε _max is an allowable processing error, which is a preset value. Further, ρ'is a value indicating the degree to which the path is close to an arc, and for example, the machining errors ε (k + h) and ε (kh) at positions that are moved back and forth by a predetermined time h with respect to the machining error ε (k). Calculate using the ratio of.

[0070]

[Equation 10]

Here, max (ε (k + h), ε (kh)) is ε (k
+ h)> εn (kh) max (ε (k + h), ε (kh)) = ε (k +
h) is the function. If ε (k) is the machining error at the corner, ε (k) is sufficiently larger than the errors ε (k + h) and ε (kh) in the peripheral area, so max (ε (k + h) , Ε (kh)) /
ε (k) approaches 0. On the other hand, when ε (k) is the machining error of the arc portion, ε (k) is almost equal to the peripheral errors ε (k + h) and (kh), so ε (k + h) = ε (kh )) / Ε (k) approaches 1. Here, g (x) is a function that satisfies g (0) = 0 and g (1) = 1, and for example, the above-mentioned equation 6 is used.

As described above, according to the present embodiment, the permissible feed rate F is determined based on the surface-to-surface error between the target machining shape Sld ′ and the predicted machining shape Sld and the machining shape error ε (i).
Since d'is calculated, the allowable feed speed required for moving on the original route can be accurately obtained without being affected by the error included in the command route.

In the equation 9 , Fr 'and Fc' according to ρ '.
However, another equation may be used as long as it is Fr ′ at the arc portion and Fc ′ at the corner portion. Similarly, the function g (x) used in Equation 6 is also g (0) = 0, g
(1) Another function may be used as long as = 1 is satisfied.
Further, the method of obtaining ρ ′ in Expression 10 may be another function as long as it is 1 at the ideal arc portion and 0 at the ideal corner portion.

Embodiment 5. The present embodiment relates to a numerical control device for automatically setting a transfer function in consideration of acceleration / deceleration, servo system, and machine characteristics in the same manner as the second embodiment in the fourth embodiment. FIG. 11 is a block diagram showing the configuration of the numerical control device according to the present embodiment. Figure 11
In the figure, 8 is a transfer function automatic setting unit. The other components are the same as those in FIG. Since the operation of the transfer function automatic setting unit 8 in this embodiment is the same as that in the second embodiment, its explanation is omitted.

Sixth Embodiment Although the target machining shape is set in advance in the fourth embodiment, the target machining shape is data created at the stage of shape design, and only the program is used in the actual machining site, and the target machining shape data is Often not available. Further, when the machining program is not created by the three-dimensional CAM or when the machining program is created by measuring the position of the surface of the wooden pattern by digitizing, the target machining shape data is not created. The present embodiment provides a method for easily calculating a target machining shape from a machining program in such a case.

In the present embodiment, the processed shape is calculated using the block information B _D. FIG. 12 is a block diagram of the numerical control device according to the present embodiment, and FIG. 13 is a flow until the target machining shape is calculated from the machining program. In the figure, reference numeral 11 denotes a target machining shape calculation unit, in which a material shape and a tool shape are stored. All of these are the same as the shape stored in the processed shape prediction unit 9.

[0077] Then the method for calculating the target machining shape data in this embodiment will be described with reference to the flowchart shown in FIG. 13. Prior to machining, the block information _BD created by the block information creating unit 2 is used as the target machining shape calculating unit 1
Every 1 block is read (ST ₆ 1). Then target machining shape calculating unit 11 calculates the target machining shape Sld 'by the block information _{B D} and material shape and the tool shape read in _{ST 6 1 (ST 6 2)} . The known method described in the fifth embodiment may be used as the method for calculating the target machining shape Sld ′.

[0078] to check whether it has reached the end of the next ST ₆ 3 in the machining program, to resume the reading of NO If the block to continue the calculation of the machining shape. If YES, the process advances to ST ₆ 4, the calculated target machining shape Sl
Input d ′ to the processing error calculation unit 10.

As described above, according to this embodiment, the target machining shape can be calculated from the machining program when the target machining shape data cannot be obtained in advance. Target machining shape Sl obtained using the method according to the present embodiment
Although d'is affected by the command path error, in the process of calculating the three-dimensional machining shape, not only a single path but a plurality of adjacent paths affect each other as a whole, so the local error is It becomes smooth and inconspicuous. Therefore, as a result, it is possible to obtain a smooth target machining shape that is hardly affected by the error. Further, by providing the transfer function automatic setting unit 8 described in the second embodiment inside the numerical controller,
It is also possible to automatically set the transfer function G (s).

Embodiment 7. In the fourth embodiment,
The predicted machining shape Sld was calculated from the predicted trajectory, and the machining error ε (i) was calculated by taking the difference from the target machining shape. The processing error ε (i) thus obtained is the allowable processing error ε _max.
The value may exceed the allowable value or may be smaller than the allowable processing error than necessary. In the die machining, it is prioritized that the trajectory errors are the same for each path, but when not only the precision of the machined surface but also the dimensional accuracy is required, it is desirable that the machining error be below the allowable value. . Further, if the processing error becomes smaller than the allowable value than necessary, unnecessary deceleration occurs and the processing cannot be performed in a short time. The present embodiment provides means for obtaining an allowable feed rate at which the processing error ε (i) is closer to the allowable processing error ε _max .

FIG. 14 is a numerical controller according to this embodiment.
FIG. 15 is a block diagram showing the configuration of FIG.
It is a flow chart showing operation of the device. First ST₇1 ~
ST ₇5, the ST shown in the fourth embodiment_Four1-ST_Four
Temporary command position P in the same procedure as 5_o1(i), prediction trajectory P₁(i)
Calculated and predicted machining shape Sld₁, Processing error ε₁(i) and
And allowable feed speed Fd₁'Is required. Next, ST₇To 6
This processing error ε ₁(i) and allowable machining error ε_maxOf the difference
Absolute value | ε_max−ε₁(i) | It is determined whether or not |
If it is cut off and it is within the predetermined value β, ST₇Permission obtained in 5
Feeding speed Fd₁'Is input to the acceleration / deceleration / interpolation unit 3.

When the above condition is not satisfied (| ε _{max
-Ε 1 (i) |> β} ) is permissible feed rate Fd ₁ obtained in ST ₇ 5
Is input to the temporary command position creation unit 5, and the temporary command position P
_o2 (i) is created. Here, when creating a provisional command position again, the value obtained by multiplying the sampling period δt to the allowable feedrate Fd ₁ 'calculated in ST ₇ 5 is used as the distance increments. In this way, the predicted trajectory P ₂ (i) is calculated from the newly obtained temporary command position P _o2 (i), and the predicted machining shape Sdl ₂ is created. As a result, the predicted machining error ε ₂ (i) and the allowable feed speed Fd ₂ ′ are again obtained. ST ₇ 2~ST ₇ 6 steps termination condition _{| ε max -ε m (i)} | ≦ β (m = 1,2, ... n) is repeated until satisfied.

As described above, according to this embodiment,
Measurement error ε₁(i) and allowable machining error ε _maxThe absolute value of the difference between
Create a temporary command position ST until it falls below a specified value₇2. Predicted gauge
Trace calculation ST₇3 and calculation of allowable feed rate ST₇4 rolls
returned. As a result, the predicted machining error ε calculated_m(i)
Is the allowable processing error ε_maxSince the value is very close to
Highly processed surface can be obtained in a short time.

In the above description, the condition that the absolute value of the difference between the machining error and the permissible machining error is less than or equal to the predetermined set value is the end condition for the prediction machining error calculation. If the absolute value of the difference between the previously obtained allowable feed speed and the previously obtained allowable feed speed and the value is equal to or less than a predetermined set value, or a combination of these AND and OR may be used as the end condition. In addition, the second embodiment
The transfer function can be automatically set by providing the transfer function automatic setting unit described in 1 above inside the numerical controller.

[0085]

According to the numerical controller of the present invention, the locus of the machining tool when the speed control of the machine tool is performed by the command path and the command feed speed commanded by the machining program is performed from the command position to the actual machining tool. Predicted based on the transfer characteristics up to the machining position, which is the position, the acceleration of the processing tool , the normal component of the acceleration, the jerk, or the position on the predicted trajectory
・ Since the allowable feed rate is calculated based on the characteristic amount that represents the vibration component of speed / acceleration or jerk and its allowable value, it is possible to obtain a highly accurate machined surface in a short time even if the command path contains an error. Can be done.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a numerical control device according to a first embodiment.

FIG. 2 is a flowchart showing the operation of the numerical control device according to the first embodiment.

FIG. 3 is an explanatory diagram showing a method of calculating a predicted trajectory.

FIG. 4 is a vector diagram showing a method of calculating acceleration and normal acceleration based on a predicted trajectory.

FIG. 5 is a trajectory of the processing tool obtained by simulation.

FIG. 6 is a block diagram showing a configuration of a numerical control device according to a second embodiment.

FIG. 7 is a block diagram showing a configuration of a numerical control device according to a third embodiment.

FIG. 8 is a flowchart showing the operation of the numerical control device according to the third embodiment.

FIG. 9 is a block diagram showing a configuration of a numerical control device according to a fourth embodiment.

FIG. 10 is a flowchart showing the operation of the numerical control device according to the fourth embodiment.

FIG. 11 is a block diagram showing a configuration of a numerical control device according to a fifth embodiment.

FIG. 12 is a block diagram showing a configuration of a numerical control device according to a sixth embodiment.

FIG. 13 is a flowchart showing the operation of the numerical control device according to the sixth embodiment.

FIG. 14 is a block diagram showing the configuration of a numerical control device according to the seventh embodiment.

FIG. 15 is a flowchart showing the operation of the numerical control device according to the seventh embodiment.

FIG. 16 is an explanatory diagram of a command path described in a machining program.

FIG. 17 is a block diagram showing the configuration of a conventional numerical control device.

FIG. 18 is an explanatory diagram for explaining the influence of an error included in a command path on machining.

[Explanation of symbols]

1 program reading part, 2 block information creating part,
3 acceleration / deceleration / interpolation unit, 4 servo control unit, 5 temporary command position creation unit, 5a look-ahead buffer, 6 trajectory prediction unit, 7
Allowable feed rate calculation unit, 8 Transfer function automatic setting unit, 9
Machining shape predicting unit, 10 machining error calculating unit, 11 target machining shape calculating unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G05B 19/416

Claims (7)

(57) [Claims] 1. A numerical control method for controlling the speed of a processing tool of a machine tool based on a command path and a command feed speed commanded by a machining program, wherein the speed control of the work tool is performed by the command path and the command feed speed. actual ago command position predicted trajectory of the working tool in the case of performing
Acceleration on the predicted trajectory of the processing tool calculated based on the transfer characteristic up to the processing position, which is the position of the processing tool.
Degree, normal component of acceleration, jerk, or position / velocity / jerk
A numerical value characterized in that an allowable feed speed is calculated based on a characteristic amount representing a vibration component of speed or jerk and an allowable value of the characteristic amount, and the speed of the processing tool is controlled to be equal to or lower than the allowable feed speed. Control method. 2. A numerical control method for controlling the speed of a machining tool of a machine tool based on a command path and a command feed speed commanded by a machining program, the speed control of the work tool according to the command path and the command feed speed. the actual from said command position predicted trajectory of the working tool in the case of performing
Calculated based on the transfer characteristic up to the processing position, which is the position of the processing tool, for a plurality of line segments that make up the predicted trajectory ,
A numerical control method, wherein an allowable feed rate is calculated based on an angle formed by each line segment and an adjacent line segment, and the speed of the processing tool is controlled to be equal to or lower than the allowable feed rate. 3. The numerical control method according to claim 1 or 2 , wherein an allowable feed speed calculated from a characteristic amount and an allowable value of the characteristic amount is used as a command feed speed. 4. A numerical control method for controlling the speed of a machining tool of a machine tool based on a command path and a command feed speed commanded by a machining program, wherein the speed control of the machining tool is performed by the command path and the command feed speed. actual ago command position predicted trajectory of the working tool in the case of performing
Calculated based on the transfer characteristic up to the machining position, which is the position of the processing tool, and based on the error between the predicted machining shape and the target machining shape of the workpiece calculated based on the predicted trajectory and the allowable value of the error. And a permissible feed speed is calculated by the above, and the speed of the processing tool is controlled to be equal to or less than the permissible feed speed. 5. The numerical control method according to claim 4, wherein the target machining shape is calculated using a command path commanded by a machining program. 6. The numerical control method according to claim 4, wherein an allowable feed speed calculated based on an error and an allowable value of the error is used as a command feed speed. 7. The method of claim 1 or 4, the transfer characteristic is numerically characterized mechanical properties of the machine tool, servo characteristics, to be calculated using at least any one of a transfer function representing the acceleration characteristic Control method.