JP2001188605A - Method for interpolating curve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the processing speed by reducing the number of calculations for finding out a curvature and reducing the whole calculation throughput in order to solve such a conventional problem that much throughput is required, much processing time is required and necessary processing can not be completed within a fixed time because the whole curve is divided into plural fine curves and the curvatures of respective fine curves are found out. SOLUTION: In the curve interpolation method for a motion controller for controlling the moving loci of various machines, plural substitutive points (A, C, D, E, B) of one of plural partial curves constituting the whole curve are set up (step 403), and when a curve of all the substitutive points in the partial curve is included in a curvature change allowance range (YES in step 404), the partial curve is divided into plural straight lines corresponding to a curvature value (step 405) and interpolation processing similar to straight interpolation is executed (steps 407-409). When the curve of the substitutive points is not included in the curvature change allowance range (NO in the step 404), divided curves are newly generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing curve interpolation in a motion control device for controlling, for example, a machine tool or an industrial robot.

[0002]

2. Description of the Related Art Spline (s) is controlled using an NC (Numerical Control) device which is one of devices for controlling motion.
pline) Curves and non-uniform rationalized B-splines [Non-Uniform
Ratio-nal B Spline, hereinafter simply referred to as “NURBS”] When performing curve interpolation based on trajectory data of a free curve shape such as a curve, the following processing is usually performed at present. First, the read curve data is analyzed and divided into minute curves. The radius of curvature of each micro-curve and the limit speed of curvature determined by the radius of curvature (the maximum speed at which the movement on the locus of the curve drawn with the curvature can be faithfully reproduced) are calculated. At the same time, a minute curve having a maximum curvature (a minimum curvature radius) is searched for. With respect to the speed of moving on the trajectory, the speed is determined on the basis of the curvature limit speed so that acceleration / deceleration can be performed within a specified acceleration (usually the maximum acceleration / deceleration of the machine). That is, when the command speed described in the NC program is sufficiently higher than the curvature limit speed of each point, the curve maximum point is a point where the speed becomes minimum. Acceleration / deceleration control is performed in which the speed of each point is determined and decelerated using the linear distance from a certain position to this curvature maximum point as a guide within the range of the acceleration.

[0003]

However, in the conventional curve interpolation method, the entire curve is divided into minute curves, and the curvature is obtained for each minute curve. The calculation for this curvature is
Extremely high throughput. Therefore, if the curvature is calculated for all the minute curves, a huge amount of processing time is required. Particularly, when performing trajectory control online, the required processing cannot be completed within a certain time, thereby increasing the speed. In the worst case, the trajectory movement is interrupted (in the case of cutting work using a machine tool, the work is marked by stopping it).
There is also a possibility that the trajectory as instructed cannot be realized. Accordingly, an object of the present invention is to provide a curve interpolation method by a motion control device capable of realizing high-speed curve interpolation by reducing the number of curvature calculations, thereby reducing the overall processing amount and improving the processing speed. It is.

[0004]

In order to achieve the above object, a first aspect of the present invention relates to a curve interpolation method for a motion control device for controlling the movement trajectory of various machines, wherein a partial curve constituting the entire curve is provided. Then, a plurality of representative points of one partial curve are selected, the curvature of the representative point of the partial curve is obtained, and if the curves of all the representative points in the partial curve are within the allowable curvature change range, This is a curve interpolation method characterized by dividing the image into straight lines having a length corresponding to the curvature value and performing an interpolation process similar to the linear interpolation. According to the first aspect of the present invention, the processing speed of the curve interpolation shape analysis can be improved, and a curve whose curvature falls within a certain range is divided into straight lines and replaced, thereby achieving the same effect as linear interpolation. Processing can be performed, resulting in a special effect that can be reduced to conventional linear interpolation. The acceleration / deceleration calculation processing conventionally used in linear interpolation can be used as it is. Furthermore, the same connection processing as in the past can be used for the connection between the curve interpolation and the linear interpolation, and the conventional device can be used.

According to a second aspect of the present invention, there is provided the curve interpolation method according to the first aspect, wherein the curvature of at least one of the representative points of the partial curve is not within the curvature change allowable range. 2. The method according to claim 1, wherein the partial curve is divided at the representative point, and the divided curve is newly defined as a partial curve to perform an interpolation process. In this way, according to the second aspect of the present invention, a remarkable effect that interpolation processing is performed on a representative point that deviates from the allowable range can be freely defined as a new partial curve.

According to a third aspect of the present invention, in the curve interpolation method according to the second aspect, a partial curve division process is performed until all of the partial curves fall within the curvature change allowable range. A curve interpolation method according to claim 2.

According to a fourth aspect of the present invention, in the curve interpolation method according to the third aspect, the number of the representative points of the partial curve can be changed. This is an interpolation method. According to the invention of claim 4,
Because the number of the representative points of the partial curve can be changed,
It is possible to perform interpolation according to the shape of the curve, such as reducing the number when the shape is smooth overall and increasing it when the shape is complex, and also to respond to the processing performance and required accuracy of the control device. it can.

According to a fifth aspect of the present invention, there is provided the curve interpolation method according to the third aspect, wherein the curvature change allowable range can be changed. .

According to a sixth aspect of the present invention, in the curve interpolation method according to the third aspect, it is possible to change a correspondence relationship between the curvature and the length of a straight line to be divided. 3 is a curve interpolation method. Therefore, according to the fifth and sixth aspects of the present invention, it is possible to change the allowable range of curvature change and the correspondence between the curvature and the dividing straight line and the length. Curve interpolation according to the accuracy can be executed.

According to a seventh aspect of the present invention, in the curve interpolation method according to any one of the first to sixth aspects, a computer-readable recording medium for recording a program to be executed by a computer. The curve interpolation method according to any one of claims 1 to 6, wherein the curve interpolation processing is performed in accordance with the operation procedure stored in the method. Thus, according to the invention of claim 7, it is possible to apply the conventional circuit device, and it is possible to improve the performance of the curve interpolation as well as to keep an excellent effect on economy.

[0011]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a circuit configuration for performing processing when performing curve interpolation, taking an NC control device as an embodiment of the present invention. In FIG. 1, 1 is an NC data reading unit, 2 is a curvature calculating unit, 3
Is a curvature determining unit, 4 is a partial curve generating unit, 5 is a straight line dividing unit,
6 is an acceleration / deceleration calculation unit, 7 is a control data output unit, 8 is input data as a control command, 9 is control output data for controlling the next-stage servo device, 10 is an NC control device according to the present invention, 11
Is a servo device controlled by control output data. An outline of processing for a command trajectory input in a NURBS curve format using this NC control device will be described.

The curve interpolation operation of the NC control device is as follows. First, the NC data reading unit 1 reads an NC program stored in the internal memory of the NC device. NURB
In addition to the command indicating S-curve interpolation,
NURB expressed by knot data, control points, and weights
The NC data in the S-curve format and the moving target speed are read in this part. FIG. 2 is a diagram illustrating an example of a curve for explaining the curvature determination in the partial curve. Next, the curvature calculation unit 2
Then, the curvature (radius of curvature) of the representative point is calculated for each partial curve. FIG. 2 divides the partial curve AB into four equal parts, and calculates the curvature using three division points (C, D, and E), and five points of the start point (A) and the end point (B) as representative points. An example is shown. Here, since the start point is the same point as the end point of the previous partial curve, it is not necessary to calculate the curvature except for the first partial curve.

After calculating the curvature of each point, the curvature determining section 3 determines whether the curvature of each point falls within a specified range. Here, assuming that the allowable range of curvature is 3 mm, the difference between the maximum value and the minimum value of the curvature of the partial curve representative point is 2.1 mm, so that the curvatures of all five representative points are within the range. , And this partial curve is divided into lengths according to the curvature. The curvature value used at this time is considered to be an error range because the curvature values are close to each other, and the curvature radius produced from the representative point is the smallest, the curvature of the starting point, the average of the curvature of the representative point, and the like. Can be considered.

FIGS. 3A and 3B are illustrations showing how a curve is divided into straight lines. As can be seen from FIG. 3A, an error (tolerance) occurs because the curve is divided and approximated to a plurality of straight lines. This error can be adjusted by the relationship between the curve and the length of the straight line to be divided. This error can be adjusted by the relationship between the curvature and the length of the straight line to be divided. Even for the same curve, if the length of the divided straight line is reduced, the error is reduced as shown in the enlarged view of FIG. However, of course, the number of straight lines increases, and the processing speed decreases.

A straight line having a length corresponding to the curvature is a short straight line when the radius of curvature is small (large curvature), and a long straight line when the radius of curvature is large (small curvature). By properly associating the curvature with the length of the straight line to be approximated, errors due to the approximation can be subtly absorbed by the influence of the curvature. In the example of FIG. 2, when the allowable curvature is 2 mm, the value of the curvature at the representative point of the partial curve AB is 2.1 mm as described above, which is outside the allowable curvature. Therefore, the partial curve AB is divided by the partial curve generation unit 4, and AC, CD, DE,
Four partial curves EB are generated, and for each partial curve, the same curvature calculation and curvature determination processing of the representative point as described above are repeated. This is repeated until all the partial curves can be approximated as straight lines, or the curvature of the representative point falls within the allowable range.

FIG. 4 is a flowchart showing an operation procedure for executing curve interpolation according to the present invention. That is, FIG.
Represents the above description in the form of a flowchart. In FIG. 2, the number of representative points in the partial curve is five including the starting point and the ending point. If the number is small, the curve where the curvature changes abruptly at the part other than the representative point does not appear on the control, it may give unnecessarily additional to the processing machine or cause a trajectory error. It could be. Conversely, if the number is increased too much, it becomes easier to cope with the curve of the complicated shape described above,
The amount of curvature calculation increases, which leads to an increase in processing time. Thus, from the above description, the present invention
Generation of new partial curves, repetition of calculation until those partial curves fall within the allowable range of curvature, change of allowable radius of curvature according to system performance and required accuracy, change of number of representative points, length of division straight line All adjustments can be performed freely.

[0017]

As described above, according to the first aspect of the present invention, the processing speed of the curve interpolation shape analysis can be improved, and the curve whose curvature falls within a certain range is divided into straight lines. By performing the replacement, the same processing as that of the linear interpolation can be performed, and the special effect that the conventional linear interpolation can be achieved is achieved. The acceleration / deceleration calculation processing conventionally used in linear interpolation can be used as it is. Furthermore, the same connection processing as in the past can be used for the connection between the curve interpolation and the linear interpolation, and the conventional device can be used. Further, according to the second aspect of the present invention, a remarkable effect that interpolation processing is performed for a representative point that deviates from the allowable range can be freely defined as a new partial curve. Further, according to the invention of claim 4, since the number of the representative points of the partial curve can be changed, the number of the representative points is reduced when the shape is entirely smooth, and increased when the shape is complicated, and so on. It is possible to execute interpolation according to the state, and to cope with the processing performance and required accuracy of the control device.
Further, according to the fifth and sixth aspects of the present invention, the allowable range of curvature change and the correspondence between the curvature and the dividing straight line and the length can be changed. It is possible to execute curve interpolation according to the required accuracy. According to the invention of claim 7, the application of the conventional circuit device is enabled, and the performance of the curve interpolation is of course improved.
It keeps an excellent effect on economy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration for performing processing when executing a curve interpolation, taking an NC control device as an embodiment of the present invention as an example;

FIG. 2 is a diagram illustrating an example of a curve for explaining a curvature determination in a partial curve according to an embodiment of the present invention.

FIG. 3 shows how a curve is divided into straight lines, and (a)
Is an explanatory diagram when a part of the curve exceeds the allowable curvature range.

FIG. 4 is a flowchart showing an operation procedure for executing curve interpolation according to the present invention;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 NC data reading unit 2 Curvature calculation unit 3 Curvature determination unit 4 Partial curve generation unit 5 Linear division unit 6 Acceleration / deceleration calculation unit 7 Control data output unit 8 Input data 9 Control output data 10 NC control device 11 according to the present invention 11 Servo device

Claims (7)

[Claims] 1. A curve interpolation method of a motion control device for controlling a movement trajectory of various machines, wherein a plurality of representative points of one partial curve are selected for a partial curve constituting an entire curve, and the representative of the partial curve is selected. If the curvature of the point is found, and if the curves of all the representative points in the partial curve are within the allowable range of curvature change, the curve is divided into straight lines having a length corresponding to the curvature value, and interpolation similar to linear interpolation is performed. A curve interpolation method characterized by performing processing. 2. The curve interpolation method according to claim 1, wherein the curvature of at least one of the representative points of the partial curve does not fall within the curvature change allowable range. 2. The curve interpolation method according to claim 1, wherein the interpolation process is performed by defining the divided curve as a new partial curve. 3. The curve interpolation method according to claim 2, wherein partial curve division processing is performed until all of said partial curves fall within said curvature change allowable range.
Curve interpolation method described in 1. 4. The curve interpolation method according to claim 3, wherein the number of the representative points of the partial curve can be changed. 5. The curve interpolation method according to claim 3, wherein the curvature change allowable range can be changed. 6. The curve interpolation method according to claim 3, wherein the correspondence between the curvature and the length of a straight line to be divided can be changed. 7. The curve interpolation method according to claim 1, wherein a program to be executed by a computer is recorded, and the program is executed according to an operation procedure stored in a recording medium readable by the computer. 7. The curve interpolation method according to claim 1, wherein the interpolation processing is performed.