At present, PROTEL, TANGO, ORCAD, P-CADEE and other printed circuit board CAD software design PCBs are widely used at home and abroad. PCB graphics files generated by PCB-CAD can be input into the photoplotter to obtain photolithographic positive films; The automatic programming process generates NC commands for the processing of the copper plated pad holes for the PCB dedicated CNC drilling machine. However, in the generation of NC instructions, the existing PCB automatic programming software determines the order of the drilling by using the XY coordinates of the hole positions to be arranged one by one by some convention.
Obviously, the resulting drilling path is not the best route, which affects production efficiency. For those specialized manufacturers of medium and large-scale production scales with an annual output of several thousand to hundreds of thousands of PCBs, the impact is considerable. On this issue, foreign scholars have carried out a lot of research and discussion, which shows the strong awareness of the overall process optimization.
2 The establishment of the optimal path model The PCB usually has a variety of holes of different diameters. For a hole system formed by a certain aperture, the PCB numerical control drill problem can be described as: date received from the original: 2000~03- 25; revised draft received date: 2001~03~05. Wang Wei, male, born in 1964, lecturer, the main research direction is CAD/CAM virtual manufacturing. Liu Huixia, starting from the knife point, processing all the holes without repeating and not missing, and then returning to the problem, is an NP-complete problem. At the tool change point of the TSP proposed so far, the next type of hole change tooling and machining is performed. For the NC programming, there is a processing sequence (route) of how to arrange the holes, so that the short-distance movement time is the shortest, that is, the so-called optimal path. Obviously, this problem can be attributed to the famous travel salesman problem, in which the drill bit plays the role of the sales clerk, and the objective function of the best travel route can be selected as the shortest flight time of the tool or the shortest time of the idle travel. Discussion and analysis: PCB numerical control drilling is a numerical control machine with point control. When the tool of this machine moves from one point (hole) to another (hole), it usually moves at the same time along the XY axis. When the respective distances along the XY axis are different, the coordinate value is smaller and the motion is first completed to reach an intermediate point (for example, from 0 to A). The other coordinate will continue to move from the intermediate point to the end point (such as 1 point) along the coordinate axis direction, and the motion track of the tool change point 0 will be returned from the tool change point 0 through é¥«2-3-5 as shown.
It can be seen that the tool moves from one hole to another, and its fast moving path is generally not a straight line but a broken line. Taking 0 to 1 as an example, the idle travel between two points and the idle travel time between two points t(I,)=maxIX/-X/i/Vx, IY-Y/i/Vy. where V is the work The fast moving speed of the table relative to the X or Y direction of the tool is generally Vx=Vy=V. Since the purpose of finding the shortest route is to reduce the dead time, the shortest free time calculated by calculation is used as the best measure. The objective function of the route can improve the computational efficiency. Obviously, minimizing t(/,) is more simplified than minimizing D7U.)=maxIX-X/I, IY-Y/I as the objective function for measuring the optimal path.
Various solutions can be basically divided into three categories: the exact solution heuristic method and the neural network algorithm. The exact solution can only solve the small-scale TSP problem, which is obviously not suitable for PCB problems. The best tool routing problem for PCBs is a large-scale TSP problem. Foreign scholars have done a lot of research on this problem, basically adopting the heuristic method, and the algorithm is based on the Euclidean distance between two points, namely d/=SQRT. From the previous analysis, we can know This does not match the path taken by the CNC drill. Thus, it is difficult to effectively solve this problem by using the position information or the algorithm proposed by the geometric features of the triangle inequality. The system uses the idle travel time as the objective function and uses the simulated annealing method.
Formal annealing strategy, the choice of this strategy is the most critical, because the temperature in the algorithm that affects the quality of the solution convergence is controlled by the annealing strategy. Common annealing strategies are: (e is the standard deviation of the objective function value 161).
Where c is an adaptive annealing strategy, this paper chooses this annealing strategy.
The SA algorithm is a general domain-independent and powerful combination optimization algorithm that can escape the local optimum with probability climbing. For TSP, it is one of the better models. The number of cities that can be processed now reaches 6000. As many.
3.3 Run the example 0 to write, debug and run on the Pentium I processor 650MHz computer. It is a 64) drilling path map generated by general PCB-CAD software. It is a drilling path map generated by the algorithm of this paper. Comparing, 3 can be seen that the empty travel of the tool is shortened by 36.5%. Through a large number of examples, it is found that the optimized path obtained by the algorithm is more certain than the XY coordinates of the hole position by the general PCB-CAD software. The method of successive programming is indeed functionTSP - it means to exchange vertex A; and a, to see if it can produce a shorter travel path, the stroke of the travel is obvious, generally more than 25%, the method is practical, reliable and can be compared Good solution.
4PCB optimal CNC programming system bookmark4 PCB numerical control drilling is the best way to determine the path, effectively solve the problem of optimized CNC programming of PCB processing process. Based on this, an automatic PCB programming system was developed, and its workflow is as shown.
Drilling data file pre-processor optimal path to determine the post processor DNC communication interface PCB numerical control drilling system PCB optimal CNC programming system work process is the difference generated in different types of PCB-CAD system The formatted PCB drilling data file is handed over to the pre-processor. The role of the pre-processor is to analyze and identify the contents of the drilling data files generated by different CAD systems, and extract the position information according to different aperture families, and convert them into a unified data file form as the optimal path model for determining a certain drill bit. The data source; the optimal path of the hole is determined by the optimal path module and then handed over to the post processor for processing. The task of the post processor is to read the different drill diameters, the optimal travel path model position information and the numerical control characteristic file of the specific CNC machine tool by the scanner, analyze it by the semantic analyzer and generate the numerical control instructions corresponding to the CNC machine tool. Finally, The CNC command is transmitted to the corresponding CNC machine by the DNC communication program.
In this paper, the optimal route of PCB numerical control drilling is reduced to TSP problem. The objective function and the three important functions of solving the optimal path are solved by SA algorithm: the generating function Gnerate accepts the function Accept and the temperature update function Update. The strategy plays an important role in simulated annealing, directly affecting the quality of the TSP solution.
The algorithm has been successfully applied in laser numerical control drilling and trial in PCB numerical control drilling CAM system. The algorithm effectively solves the problem that the tool path is long in the multi-work, and the machining efficiency is low due to the idle stroke, so that the numerical control drilling process can be optimized.
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