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Interference of position and orientation
Designers and manufacturers should check jointly that a provided product can be assembled, without interference between parts, before the product to be manufactured. Similarly, all the CAD tools presently have the potential to directly analyze the possibility of a specified assembly plan for a product.
An assessment of previous assembly sequence and optimization research explains that most previous assembly planners apply either feature-mating or interference-free techniques to find assembly part interference interaction. In both feature-mating and interference-free techniques focused upon the basic geometrical data and restrictions for the designed product, which are generally contained in connected CAD files.
When completely automate the procedure of creating a professional assembly plan, geometrical information for CAD models should be automatically taken from CAD files, analyzed for interference relationships between components in the assembly, and then designed for utilized the assembly analysis tools. Most of the previous assembly sequence planners do not have the potential to complete the three tasks; they need users to manually input part attributes or interference data, which is so time-consuming.
Determining Interference Relationships between Parts
In automated assembly schemes, most parts are assembled along with the principal axis. Hence, to fine interference between parts while assembly, the projected technique referred six assembly directions along with the principal assembly axis: +x, -x, +y, -y, +z, and -z. But, the method could be improved, to think other assembly directions, as required. The projected system uses projection of part coordinates onto planes in three principal axis (x, y ,z) to find the obstruction between parts sliding along some of the six principal assembly axis. The projections overlap between any two parts in a specified axis direction shows a potential interference between the two parts, when one of the two parts slides along the specified direction, with respect to the other. Vertex coordinates for overlapped projections are then evaluated to find if real collisions would happen between parts with overlapped projections. The planned process stores the determined interference data for allocated assembly direction in a group of interference free matrices, for compatibility with previous planners of assembly.
The swept volume interference and the multiple interference detection systems are appropriate for three-dimensional interference determination between B-REP entities. But, both techniques were developed for real-time interference detection between two moving parts in a simulation environment. As a result, these two techniques are expensive in computationally. For the assembly planning issue, actual collision finding capacity along subjective relative motion vectors is not require. Instead, a efficient computational technique is required for finding if two parts will collide when they are assembled in a specified order along any one of the six principle assembly axis.
An interference-free matrix shows interference between two components, when one component is moved, in a given assembly direction, into an assembled location, with another component already in an assembled location. Assembly actions that result in interferences are denoted as ‘0’in the matrix, and assembly actions that do not result in interferences are denoted as ‘1’in the matrix.
As shown in figure 4.4., the interference-free matrix of an assembly having three parts, for assembly movement sliding from infinity of negative toward infinity of positive along the +x direction is as follows:
Fig.4.4. Interference of three parts
Interference-free matrix for sliding in the +x direction:
The row in the Interference-free matrix indicate the components being shifted during a given assembly operation, and the column indicate the parts that have previously been assembled. Hence, since matrix element (2, 1) is equal to ‘0’,if Part-1 is assembled initially, and after that Part-2 is assembled in the direction of +x, Part-2 will collide with Part-1. Similarly, matrix element (1, 2) is equal to ‘1’,if Part-2 is assembled initially, and then Part-1 is assembled in the direction of +x, Part-1 will not collide with Part-2. As a part cannot be assembled after itself, all elements in the diagonal matrix are set to ‘0’.As a whole, six matrices are utilized to show interference relationships between parts in the six principal axes. When robotically creating interference-free matrices, the projected algorithm finds matrix elements row by row. When two parts would interfere through assembly in a given direction, the program inserts a ‘0’in the corresponding matrix position; or inserts as a ‘1’.
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