The automatic positioning of the workpiece proposed by the author makes the workpiece coordinate system automatically adapt to the processing requirements of the machine tool. This method differs from the traditional method of correction in that instead of trying to “right†the workpiece, it measures the skew angle and offset of the workpiece placed on the workbench, and then based on this declination and offset, through the automatic Correct the part's machining program to ensure that qualified parts are machined. This method can reduce the auxiliary time occupied by workpiece positioning and clamping, and it can greatly exert the high efficiency of CNC machining.
Fig.1 Relationship between machine coordinate system and workpiece coordinate system
1 Automatic workpiece positioning principle Measurement of the workpiece position To illustrate the problem and consider the actual clamping situation, let the workpiece be skewed only in the XOY plane. When workpiece mounting is skewed, the position of the workpiece should be measured first to determine the relationship between the machine coordinate system and the workpiece coordinate system. Let Fig. 1 be the workpiece with skewed setup. The outer contour is O'ABC, X'O'Y' is the workpiece coordinate system, and XOY is the machine coordinate system. Using the measuring head to measure two points along the O'A edge, the center coordinate (x1, y1), (x2, y2) of the probe is displayed, and then the other two points (x3, y3) are measured along the O'C edge. ( X4, y4), from the above 4 points and considering the probe radius r, the coordinates of the O′ point and the inclination angle of the O′A side are a=tan-1[(y2-y1)/(x2-x1) ]x=(k1 x1-k2 x3-y1+y3)/(k1-k2)+rcos [(b+a)/2]/sin[(ba)/2] ∆y=[( k1 y3-k2 ) Y1)+k1 k2 (x1-x3)/(k1-k2)+r sin[(b+a)/2]/sin[(ba)/2]
Where: k1 = tana k2 = tanb = ( y3-y4) / (x3-x4)
Figure 2 block diagram
The coordinate transformation is set at a point coordinate value (x', y') in the workpiece coordinate system X'O'Y'. If the known workpiece coordinate system X'O'Y is translated with respect to the machine coordinate system XOY, ∆x, ∆y, And rotate an angle a, the coordinate value of this point in the XOY coordinate system, can be found as x=x'cosa-y'sina+∆xy=x'sina+y'cosa+∆y automatic positioning method And the block diagram finds a, ∆x, and ∆y from the measurement points. From the coordinate transformation formula, the coordinate values ​​in the original numerical control code can be corrected, new NC codes can be generated, and new numerical code processing can be used to obtain the original method. The same processing result. The actual operation of this method is very simple, that is, only the coordinates of the four points are measured and input into the computer. The work of calculating and correcting the original numerical control code can be automatically completed by a programmed program. Because only a simple calculation and correction of the coordinates in the original numerical control code is required, the program can be conveniently implemented in Borland C++. The block diagram of the program is shown in Figure 2. 2 Example The workpiece shown in Fig. 3 is used to process the inner cavity contour ABCD. The coordinate of each point is A(10,10), B(60,10), C(60,40), D(10,40). The tool path is indicated by the arrow. The original numerical control code is N10 G90 G54 G00 X40.0 Y30.0: N11=15.0, N12 G41 G01 X40.0 Y10.0 F100 D01: N13 X60.0 Y10.0: N14 X60.0 Y40.0: N15 X10.0 Y40.0: N16 X10.0 Y10.0: N17 X40.0 Y10.0: N18 G40 X40.0 Y30.0: ...
Figure 3 processing examples
After installation of the workpiece is skewed, the known probe radius r is 10mm, measured (10.92, -8.26), (60.84,-5.64), (-9.58, 40.62), (-8.01, 10.66), and substituted into the modified After the program, the new NC code can be output as N10 G90 G54 G00 X40.88 Y33.25: N11 Z15.0: N12 G41 G01 X41.92 Y13.28 F100 D01: N13 X61.89 Y14.33: N14 X60.32 Y44.29: N15 X10.39 Y41.67: N16 X11.96 Y11.71: N17 X41.92 Y13.28: N18 G40 X40.88 Y33.25:... Processing with the new numerical control code can be obtained with The same processing results of the original method, obviously the processing accuracy will not change. 3 Conclusion An automatic positioning principle based on the machined workpiece is proposed. This method can relax the requirements for the installation of the workpiece, and can obtain the same processing results as the original method, which has certain practical significance for shortening the installation and adjustment time of the workpiece and improving the production efficiency.
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