Research On The Interpolation Of NURBS Based On FPGA

With the development of industrial demand and people’s aesthetic level, more and more complex surface is used to design project. Depending on its excellent quality in math and algorithm, NURBS has been widely used, however, the NURBS interpolation data is too much, the machining part is always made with rough surface and the processing efficiency is low when they made in traditional way. So it is extremely urgent to carry out research on direct numerical control machining which in support of NURBS curve and surface.NURBS direct interpolation is complicated and the key to solve the CNC interpolation problem is improving the computing speed of interpolation. In order to make the NURBS interpolator which meets the requirement of high interpolation speed, this paper studies NURBS interpolation from two aspects of interpolation algorithm and hardware platform.Direct NURBS interpolation mainly includes two steps:get the NURBS curve parameter according to the interpolation accuracy and calculate the trace point on the curve based on the anticipated parameter. After analyzing the characteristic of the two calculation, a new direct NURBS curve interpolation strategy is proposed:decrease the parameter calculation time in case of not affecting interpolation speed, allowing acceptable calculation error; taking the advantage of parallel execution of FPGA, carry out the calculation from anticipated parameter to curve trace point in hardware, improving the interpolation speed.Based on the SOPC technology, the whole system was made on a Cyclone FPGA chip of Altera company. With the Software and hardware combination design, Nios Ⅱ soft processor is made in FPGA for preprocessing and parameter calculation and the Verilog HD1is used to make the hardware for trace point calculation. In order to reduce the communication burden of system, FPGA internal resource is used to transmit the parameter signal.In this experiment, the user access interface was developed based on Nios II IDE platform, then all NURBS parameters could be input into interpolator. Besides, each module in FPGA should save the parameters.Finally, direct NURBS interpolation was tested, and the experimental data shows that0.5ms was used in one interpolation calculation. The contrast design with only software shows that the advantage of calculation in FPGA hardware is important. Comparing to software, The calculation speed increases about30times in FPGA.