JPH0726809B2 - Workpiece position coordinate correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention relates to an NC (numerical control) machine tool, which is capable of automatically and accurately performing coordinate correction according to the installation position of a workpiece. The present invention relates to a coordinate correction method.

"Prior art" One of the methods of using a vertical machining center is to place a workpiece on a table, the workpiece coordinate system (work coordinate system), and the coordinate system assumed by the NC program (reference coordinate system). There is a method in which and are processed by matching the positions of the workpieces. This work of correcting the workpiece position is time consuming and cumbersome, but recently, in order to facilitate this, a method of inserting a contact probe for measurement on the spindle to search the workpiece position and moving the coordinate system (hereinafter, referred to as 1) has been developed (for this technique, see Japanese Patent Laid-Open No. 58
-120109 gazette).

The first method will be further described. When machining with an NC machine tool, the workpiece must be placed in the position and orientation assumed in the machining program. Therefore, the setting work in which the workpiece is placed on the table and the position and the posture thereof are matched is the work before machining. However, this setting work is extremely difficult and requires a long time because it requires precision.
The first method is a method of simplifying this work and matching the reference coordinate system of the machining program with the workpiece coordinate system of the workpiece currently placed.

That is, as shown in FIG. 4, after the work piece 2 is placed on the table 1, the contact probe 3 is inserted into the spindle (not shown) and the tip thereof is brought into contact with various parts of the work piece 2, and the coordinate values thereof are To detect. Based on the detected value, the work coordinate system is corrected to be shifted or rotated in order to match the reference coordinate system of the machining program. For example, in the case of FIG. 4, the work coordinate system after correction is obtained by shifting the origin of the reference coordinate system to the point (x ₀ , y ₀ ) and rotating the coordinates by θ ₁ degrees around this point.

In contrast to the above first method, there is a second method using a visual device. That is, a method of imaging a work with a visual device and obtaining the position of the work from the image has been developed in combination with a robot (JP-A-60-79413).

"Problems to be Solved by the Invention" The conventional methods described above have the following drawbacks.

(1) Disadvantages of the first method Although the first method is convenient, there is no doubt that human intervention is involved, and it is troublesome to replace a work piece or attach a plurality of work pieces. Work was occurring.

That is, in this method, since the contact probe operation is performed manually in order to find the position of the workpiece, a human must be present. In other words, when a plurality of identical workpieces are machined individually, the work of coordinate adjustment occurs each time each workpiece is placed on the table. Further, when a plurality of workpieces are simultaneously placed on the table for machining, centering work (coordinate matching work) is required every time one machining is completed.

For example, as shown in FIG. 4, not only a workpiece having a simple shape with an end face as a reference, but also a hole center as a reference, a line connecting the center coordinates of holes as a reference, and various work coordinate systems are used. Settings are required for each workpiece. for that reason,
The creator of the machining program needs to convey the intention to the operator, but it may not be as expected because complicated work or calculation of offset amount may occur.

More specifically, in the machining of the work W shown in FIG. 5, the hole A having a center point of O ₁ (x ₁ , y ₁ ) and the center point of O ₂ (x ₂ ,
The straight line connecting the center points of the hole B of y ₂ ) has an angle of θ degrees with the X-axis coordinate of the machine coordinate system, and the center coordinate of the hole A (x ₁ ,
Assuming that the workpiece is placed on the table as shown by this solid line, the outline of the coordinate system X _W -Y _W with the origin of y ₁ ) is used as the reference coordinate system. When the machining program is programmed, the operator searches the holes A and B with contact probes, finds the center coordinates of the holes A and B, and from the coordinate values, the angle of the straight line connecting those points with respect to the X axis. And the deviation of the origin must be calculated to correct the difference between the reference coordinate system and the work coordinate system.

(2) Disadvantages of the second method The second method, that is, position recognition by a visual device has a drawback that required accuracy cannot be obtained because of limitation due to the resolution of the camera.

The present invention has been made under such a background, and provides a workpiece position coordinate correction method capable of realizing highly accurate coordinate correction according to the position of a workpiece by using a visual device and a contact probe together. The purpose is to provide.

[Means for Solving Problems] In order to solve the above problems, the present invention provides a numerically controlled machine tool that images a workpiece installed on a table with a visual device, and based on the image data. , The feature of the workpiece is calculated, the feature is compared with a feature group stored in advance in the feature table, and reference point data and a machining program number indicating a reference point for coordinate alignment of the workpiece are calculated. A first step of calculating, a second step of calculating the rough position of the reference point indicated by the reference point data calculated by the first step on the image data and storing it in the memory, and a pre-stored program Of the three, the one corresponding to the machining program number is selected, and the rough position stored in the memory is converted into the rough position on the actual table. Step, and the rough position calculated in the third step is used as a target to perform automatic centering by the contact probe, and based on the obtained precise position data, the reference coordinate system and table of the selected machining program are obtained. And a fourth step of performing correction so as to match the coordinate system of the workpiece above.

[Operation] According to the above method, the processing program number is designated from the characteristics of the image data of the visual device, and the processing program corresponding to this is read. That is, since the machining program is determined according to the characteristics of the workpiece, even when different workpieces are sequentially placed on the table, the machining program corresponding to each workpiece is automatically selected. Moreover, since the coordinates and the like are corrected for each selected machining program, machining suitable for the posture of the workpiece is automatically performed.

In this case, the correction of the coordinates and the like, the rough position of the reference point determined from the characteristics of the image data is first obtained on the image data, then this rough position is converted into a rough position on the actual table, Then, the precise position is measured by the contact probe with the rough position data as a target, and the coordinates and the like are corrected according to the precise position.

In this way, the deviation of the position or orientation (including coordinate rotation) of the work piece that occurs when the work piece is placed on the table can be corrected or corrected without the need for manual labor, and thus the trouble of the conventional setup can be eliminated. It also enables continuous machining operation of multiple workpieces. Therefore, the automatic operation time can be lengthened.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an electrical configuration of a main part of an NC machine tool to which the present invention is applied.

In the figure, 10 is an image processing apparatus and 20 is an NC apparatus.

The image processing device 10 includes a TV (television) camera 11 mounted on a spindle head of a machine tool for capturing an image of a workpiece.
An image memory 12 for storing the captured image, a data memory 13 for storing a feature table 13a described later, and a control program such as a workpiece recognition program,
The control unit 14 recognizes the posture and position of the workpiece, an input / output device 15 in which a CRT display device and a keyboard are integrated, and an interface 16 for exchanging data with the NC device 20.

The data memory 13 has a feature table 13 shown in FIG.
Stores a.

The feature table 13a stores the area which is the feature amount of the workpiece, the program number corresponding to each workpiece, and the data number for coordinate adjustment.

This coordinate alignment data number is, for example, the holes A and B in FIG.
Like the center point of the, it is attached corresponding to the position data required to obtain the posture and position of the workpiece. Then, from the coordinate alignment data number, the content for coordinate alignment is known, and corresponding position data is calculated in accordance with the content and stored in the data memory 13. This position data is
It is obtained by analyzing the image data on the image memory 12 and performing a certain calculation.

On the other hand, the image processing apparatus 10 is used to set the feature amount. That is, after photographing the target work piece and calculating the area on the image memory 12, the worker inputs the input / output device.
The area 15 and the machining program number are paired and registered in the feature table 13a by operating 15.

The area is calculated by counting the bits of the portion corresponding to the workpiece on the image memory 12.

FIG. 3 is a diagram for explaining how to determine the area. In this figure, the pixel value is "1" inside the workpiece W and "0" outside, and the number of "1" is counted as the area. Therefore, the area is sampled not as the actual area of the workpiece but as the amount occupied in the image memory 12. And
As a result of referring to the characteristic table 13a, the program numbers having the same area are sent to the NC device 20 through the interface 16 together with the position data.

Next, the configuration of the NC device 20 will be described.

The NC device 20 is connected to the interface 16 in the image processing device 10 to exchange data with the interface 16, a data memory 22 for storing the rough position of the centering position on the workpiece, and a work coordinate system. Coordinate system offset memory 23 for storing the offset amount of X, a control unit 24 for storing and executing a control program, an I / O interface 25 for supplying the output signal of the contact probe 3 to the control unit 24, an X
A current position counter 26 that counts the current positions of the axes and the Y-axis.

The current position counter 26 is an X-axis and Y-axis drive motor M1, M2 whose rotation is controlled by a drive signal from the NC device 20.
It counts the pulse signals from the pulse generators E1 and E2, which are connected to, and outputs the movement amount of the table.

Next, the operation of this embodiment will be described.

The main operation of this embodiment is as follows.

(1) The type, position and orientation (rough position on the image memory 12) of the workpiece are calculated from the image data, and the machining program corresponding thereto is selected.

(2) The processing of the workpiece position correction program at the head of the selected machining program is started.

(3) After the rough position of the workpiece on the table is calculated from the rough position on the image memory 12, the precise position is calculated based on the output of the contact probe 3, and the position correction of the work coordinate system is executed.

(4) In the corrected work coordinate system, the machining program is executed and machining is performed.

(5) The workpieces are conveyed one by one to the field of view of the camera 11, and the operations (1) to (4) are repeated.

Hereinafter, these operations will be described in detail.

(1) Index of workpiece type, posture, position and machining program The operator places the workpiece on the table and starts the workpiece recognition program (created by a custom macro) of the NC unit 20. Let

The workpiece recognition program inquires the type of the workpiece on the table through the interface 21 with the image processing apparatus 10.

When an inquiry about the type of workpiece is received from the NC device 20, the image processing device 10 takes in the workpiece on the table as image data, calculates the features required for discrimination, and the position data required for coordinate adjustment, and the features Are searched for in the feature table 13a. That is, the image processing apparatus 10 takes an image of a table with the camera 11, obtains image data, extracts individual workpieces from the entire data of this image, and calculates the characteristics and position data thereof.

Generally, such features include the area of the object, the position of the center of gravity, the perimeter, the number of holes on the surface, the area of holes, etc. (Measurement and control VoL.22, No.3 recent image measurement technology). From the calculated features, the feature table 13a is referred to search for a matching feature, and the corresponding program number when the feature is matched is selected.

In the case of this embodiment that can be distinguished only by the area, the feature table 13a, the area which is the feature amount, the program number,
It has already been described that it is composed of coordinate alignment data. As a result of referring to the characteristic table 13a, the program numbers having the same area are sent to the NC device 20 through the interface 16. When sending the program number, the coordinate data of the feature table 13a and the position data of each location corresponding to the number (data on the image memory 12 and the coordinate system specific to the workpiece from the image) , For example, determined from the coordinate system with the center of gravity as the origin).

(2) Execution of workpiece position correction program The NC device 20 receives the above program number, selects a necessary machining program, and starts execution of this machining program. At the beginning of the machining program, a workpiece position correction program for calculating a rough position of the workpiece is provided as a subprogram.

This work position correction program calculates the approximate position of each position of the work on the table, that is, the rough position on the table from the position data received from the image processing device 10, that is, the rough position on the image memory 12. To do. That is, position data on the image memory 12 from the image processing device 10,
Also, the reference data for coordinate alignment is received, and the position data in the coordinate alignment data is calculated in consideration of the scale of the image memory 12 and the actual product, and the rough position of each location of the actual workpiece is calculated. This rough position is data required to bring the contact probe 3 to each of the above-mentioned locations.

In this case, if the entire surface of the table cannot be stored in the image memory 12, the table is automatically moved to store the target workpiece in the image memory 12. The workpiece position at this time is calculated by referring to the data of the current position counter 26 such as the X-axis current position counter and the Y-axis current position counter. The calculated data is stored in the data memory 22 of the NC device 20.

(3) Execution of work coordinate system correction program After execution of the work position correction program, this program provided as a sub-program on the machining program is executed. This program calls the rough position of the centering position, which is necessary for coordinate adjustment, from the data memory 22, inserts the contact probe 3 on the spindle, and activates the so-called automatic centering function to perform probe tip and machining. Knowing the position coordinate value of the point of contact with the object, calculating its precise position and correcting the coordinate position necessary for this workpiece. As a correction method, NC device 20
The offset function of the coordinate system, which is the function of, is used. This function has functions of shifting and rotating the coordinate system. The offset value thus measured is stored in the coordinate system offset memory 23
Stored in.

The reason for obtaining the rough position in the above item (2) is to improve the measurement speed. That is, it takes too much time to search the end face by moving the contact probe 3 at a low speed from the beginning to search the end face position. Further, in the case of the hole center coordinates, since it is unknown where the hole is, it cannot be practically searched by the contact probe 3.

On the contrary, it is difficult to know the work position accurately from the image data. The accuracy of position recognition by an image depends on the resolution of the camera 11 that captures the image. 512 × 5 with the current camera
Since it is about 12 (vertical × horizontal) bits, if the table size is 400 × 1000 mm, the vertical direction is about 0.8 mm and the horizontal direction is about 2 mm, which cannot be used for position correction as it is. . Even if a technique such as dividing and photographing is used, the resolution is about 1/2 to 1/10, which is less than the required resolution of 1 μm. Therefore, it is practical to use the contact probe 3 together.

The coordinate value obtained as a result of the measuring operation, that is, the precise position is used to correct the work coordinate system so as to match the current position and orientation of the workpiece, and match the coordinate system with the machining program.

(4) Execution of cutting program After the offset of the coordinate system, the cutting program is executed in the coordinate system to execute normal cutting.

Since the above operation is automatically performed, it is not necessary to manually perform a troublesome centering operation for a work placed on an arbitrary position on the table.

When there are a plurality of workpieces on the table, the main program of the NC device 20 (a program including the workpiece recognition program) is used so that the workpieces can be moved one by one into the view of the camera 11 by moving the table. The amount of movement is set to, which is set through the CRT operation panel of the NC device corresponding to the workpiece placed on the table by the worker. That is,
The main program executes processing in the following procedure.

a) Execution of the work piece recognition program b) Movement command c) Execution of the work piece recognition program d) Movement command ... End code Also, as means for knowing the movement amount required to bring the work piece into the field of view of the camera 11, Move the table manually,
There is a method of referring to the movement amount when the target workpiece is displayed on the CRT display device that displays an image.

Next, the operation of the embodiment will be described more specifically with reference to FIG. In the figure, it is assumed that the position of the work W shown by the solid line is the position of the work assumed by the program, and the work W'shown by the dotted line is the position actually placed on the table.

When the worker starts the workpiece recognition program, the workpiece W'shown by the dotted line is taken into the image memory 12.
The area of the workpiece W'is calculated by counting the number of dots on the image memory 12. In this case, the number of dots is 262
, The workpiece W'is
From a, it is recognized as a work piece with a program number of O1034.

At the same time, the hole A ′ corresponding to the coordinated data number 2
Coarse positions of B'on the image memory 12 are obtained and stored in the data memory 13. The obtained rough position data is sent to the NC device 20 through the interface 16 and stored in the data memory 22 in the NC device 20.

Upon receiving each of the above data, the control unit 24 in the NC device 20
O1034 Start the program. A work position correction program is provided at the head of this program.

This workpiece position correction program is based on the rough positions of the holes A'and B'on the image memory 12 stored in the data memory 22 and considering the scale, the center point O ₁ of the hole A'on the table. ′ (X ₁ ′, Y ₁ ′) and the center point O ₂ ′ of hole B ′
Calculate the neighbor points of (X ₂ ′, Y ₂ ′).

Next, the contact probe 3 is inserted into the main shaft and its tip is
The current position counter 26 counts when the tip is brought into contact with the calculated center position of the hole A ′ and is operated in the X-axis direction and the Y-axis direction to obtain the accurate center position of the hole A ′. From this, a more accurate precise position O ₁ ′ (X ₁ ′, Y ₁ ′) is obtained. Similarly, 'fine position O ₂ also' hole B (X ₂ ', Y
₂ ′) And from these two points O ₁ ′ and O ₂ ′,
The inclination (α + θ) with respect to the X axis is calculated.

From the above data, the offset amount (x ₁ ′, y ₁ ′) of the work coordinate system is stored in the coordinate system offset memory 23,
And set α degree to the coordinate rotation function.

As a result, a new coordinate system X _W ′ −Y _W ′ having a point (x ₁ ′, y ₁ ′) as an origin and an inclination α is used as a work coordinate system for machining a dotted workpiece _W ′. It is set as the work coordinate system. Then, in this work coordinate system, the machining is started from the position of the point P ₁ ′, and the machining can be performed by the same machining program as the solid line.

[Advantages of the Invention] As described above, according to the present invention, the rough position is obtained from the image data of the workpiece, and then the precise position is obtained by the contact probe to automatically perform the position correction of the work coordinate system. Therefore, the following effects can be obtained.

(1) Even in a wide measurement range such as a table, it can be automatically performed until the precise position of the reference point is detected.

(2) The machining program corresponding to the workpiece can be corrected and operated in the coordinate system according to the posture of the workpiece.
Therefore, even when a plurality of types of workpieces are sequentially placed on the table in different postures, the automatic operation can be continued without manpower.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the essential parts of an NC machine tool to which an embodiment of the present invention is applied, and FIG. 2 is a characteristic table 13a.
Fig. 3 is a conceptual diagram showing the structure of Fig. 3, Fig. 3 is a diagram showing an image of a workpiece on the image memory 12, Fig. 4 is a plan view for explaining a conventional position correcting method for an NC machine tool, and Fig. 5 is a workpiece. FIG. 7 is a plan view showing a method of performing a coordinate correction on a placed state of an object. 3 ... Contact probe, 10 ... Image processing device, 11 ... Camera (visual device), 12 ... Image memory, 13 ... Data memory, 13a ... Feature table, 20 ... NC device.

Claims (1)

[Claims] 1. In a numerically controlled machine tool, a visual device captures an image of a workpiece installed on a table, the characteristic of the workpiece is calculated based on the image data, and the characteristic and the characteristic table are stored in advance in a characteristic table. Compared with the feature groups that are
The first step of determining the reference point data indicating the reference point for coordinate position adjustment and the machining program number for the workpiece, and the rough position of the reference point indicated by the reference point data determined in the first step are shown in the image. The second process of calculating on the data and storing it in the memory, and selecting the program corresponding to the machining program number from the programs stored in advance, and the rough position stored in the memory A third process of converting into a position, and an automatic centering by a contact probe targeting the rough position calculated by the third process, thereby selecting based on the obtained accurate position data And a fourth step of correcting so that the reference coordinate system of the machining program and the coordinate system of the workpiece on the table match. Workpiece position coordinate correction method.