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Imitation three-axis control method of virtual axis CNC machine tool (2)
Source: China Bearing Network Time: 2014-10-26
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Firstly; according to the imitation three-axis machining, the axis of the machine tool should be parallel to the plane normal of the workbench; the initial attitude of the spindle is determined to be At=0; Bt=0. and the optimal preset of the channel Ct coordinates is determined according to the shape and processing requirements of the part. Orientation Ct0.
Then; in the return reference point operation before the processing start; move the moving channel to At=0, Bt=0; Ct=Ct0 condition; make the tool axis and the work table straight; tool posture At=0, Bt=0. According to the layout of the moving channel, the initial orientations pxi, pyi, pzi (i=1, 2;...;6) of the upper six support points (the moving end points of the six driving rods) in the tool coordinate system are obtained.
If k time; the tool track command value generated by the three-axis interpolation calculation is Xk, Yk, Zk; then the tool posture is stable; the coordinate value of the 6-end end point in the tool coordinate system should be unchanged; The coordinate values ​​of the moving end of the drive rod in the machine coordinate system:
Xdi=Xk+Pxi
Ydi=Yk+Pyi (i=1,2,...;6)
Zdi=Zk+Pzi (7)
According to the above-mentioned coordinates of the moving end point of the six-drive rod and the known static end point coordinates of the machine tool layout; the expected value of the length of each driving rod at k time can be obtained by the following formula; that is, the real-axis coordinate corresponding to Xk, Yk, Zk Value: (8)
Coordinates of the static end points of the Xji, Yji, and Zji six drive rods in the machine coordinate system
6 Real-axis space six-axis linkage control virtual axis space tool track generation is a kind of coarse interpolation; when the feed rate is high; the coarse interpolation straight line segment will be longer. Therefore; to ensure the stability of the six drive rod linkage; The following fine interpolation can be performed in the real axis space.
Firstly, the interpolated straight line segment of the virtual axis space (three-dimensional space) is transformed into a straight line segment of the real axis space (six-dimensional space) through the true-false mapping; the length is: (9) where Li0 is at the beginning of the coarse interpolation cycle The real axis coordinate value is then; the moving interval of the real axis spatial orbit in each fine interpolation period is obtained: Dl=L/(T1/T2) (10) where T1, T2 coarse, fine interpolation sampling period; ms Therefore, the amount of movement of each driving rod from the beginning of the straight line segment to the end of the nth fine interpolation period is: DLin=n×Dl×(Li-Li0)/L (i=1,2,...;6) (11 Further; the following formula can be used to obtain the practical value of each drive rod length at n hours; that is, the real axis motion command value is: Lin = Li0 + DLin (i = 1, 2, ...; 6) (12) Finally; The decoupling follow-up control system [3] ensures that the practical length of the drive rod is in common with the desired length; that is, the real-axis linkage control of the satisfactory tool track demand can be achieved.
7 The system completed the virtual axis machine tool simulation three-axis control system according to the proposed method; its basic composition is shown in Figure 3. The system is based on the Pentium II microcomputer system. Mu Yong 诳ǎ å… Yun Di 挚刂 Portuguese low scale è‚ low court 涞 men's side 13. Change. CNC system software by C language + 32-bit assembly language mixed programming.
When the system is in operation, the operator can input the required information through the I/O device such as a floppy disk drive; and can pass the high-end correction function supplied by the system; correct the input information. The operation of the machine tool is performed by the operator through the computer keyboard. Controlled with the CNC operation panel; information about the operation of the system is displayed graphically and graphically by the colorful CRT.
This system selects the high-precision digital communication servo system for the real axis L1～L6 of the machine tool to drive and control; each axis selects the closed-loop control method. The detection equipment selects the high-precision grating to ensure the displacement accuracy of the real axis.
The switching control in the system is used to control the logical sequence movement of the machine; such as the operation of tool replacement, pallet exchange, spindle start and stop, cooling system, stroke protection, etc. Some of the switching control will be matched with the servo control; Complete the control of the machine work process.
8 Conclusion The virtual axis machine tool has the advantages of simple mechanical layout, high rigidity, and high speed machining. However, there are also defects such as small rotation angle and narrow working area when multi-coordinate machining. Therefore, high-speed and high-efficiency machining of conventional parts should be performed. Promote its advantages. After the imitation of three-axis control; usefully reduce the complexity of the control system; then significantly reduce the total cost of the machine; it is conducive to the promotion of virtual axis machine tools in a larger range.
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