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Hardware Accelerated Real-Time Machinability Analysis of Free-Form
Surfaces
Background: It has been observed that 70-80% of the cost of producing a product is locked in at the design stage. Therefore, it is important that designers get feedback about manufacturability such that mistakes can be corrected at the design stage where the cost of correction is much lower. In the domain of Integrated Circuit (IC) design, this problem is solved by projecting manufacturing capabilities into the design through the use of Design Rule Checkers (DRCs) due to the pioneering work of Lynn Conway and Carver Mead. However, no such system exists in mechanical design. The problem of manufacturability evaluation in mechanical design is further complicated by the fact that parts are three-dimensional and there are a variety of manufacturing processes and plans that can be used to produce a single design. This project is a first cut at solving this problem. We restrict our manufacturing processes to mill machining. The basic idea is to find if a given free-form surface is machinable with a given set of cutters. This boils down to finding the accessibility of a cutter on a given free-form surface
Method:
Our research is possible only due to the advent of powerful and flexible commodity graphics hardware called Graphics Processing Units (GPUs). GPUs are powerful parallel computing devices specially designed to manipulate large amount of graphics data for the purposes of three dimensional display. However, due to the need for specialized shading methods especially in three dimensional video games, GPU vendor have enabled programmability. Some researchers have used this programmability to force the GPU to perform non-graphic computations. This technique called General Purpose GPU (GPGPU) essentially hijacks the graphics pipeline using the GPU programmability for general purpose computing.
Our method is essentially a GPGPU application.It works off of the tessellated model of the free-form surface commonly available in all CAD systems for the purposes of three-dimensional shaded display.. Instead of interpolating color for three dimensional shading, the modified graphics pipeline in our method renders interpolated vertex positions and normals to an off-screen texture. Next, a specialized fragment shader performs accessibility calculation on a per pixel basis on the projected image of the screen. The results are written to the video buffer for display.
Results:
Our current implementation runs on an NVIDIA GeForce 7950 GX2. We perform the accessibility calculation every time the view is changed. Even with this, we are able to achieve about 6 frames a second. Figures 1 shows accessibility for cutting tools of two different diameters on the tessellated model of a virus.
Shown below is a movie of the real-time accessibility calculation system. The slider bar at the top right corner of the display is used to change the radius of the ball end tool used to machine the surface.
Publications:
[1] Lysenko, M., Rahmani, K, D’Souza, R. M., 2007, Real time machinability analysis of free form surfaces on the
Acknowledgment:
This project is funded in part by the National Science Foundation (NSF). Any views, finding, conclusions, or recommendations expressed in this document do not necessarily reflect those of the NSF.
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of Mechanical Engineering-Engineering Mechanics Michigan Tech. University 1400 Townsend Drive Houghton MI 49931 Ph: 906-487-1001 |