Tham khảo tài liệu 'aerial vehicles part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 42 Aerial Vehicles discrete-time models with sampling time TS. The discretization method used was the bilinear Tustin approximation. Table 1 presents the discretized polynomial transfer functions. Correctors Continous-time Discrete-time side . . 1 Cy s 10 X 1 . - C V z y z - forward . 10 X i 05 s . CVx z 7 z -1 Table 1. Correctors discretization using Tustin bilinear approximation with fS As during EMD design a specific binary format was defined to avoid offset and stability problems. Once again we used the Filter Design and Analysis tool as well as the Fixed-point Blockset tool. A first approximation gave two signed fixed-point binary formats 9 bit and 8 bit for the integer part mI of the forward and side correctors respectively 10 bit for their decimal parts mD. However simulations of the full feedback control system showed that accuracy was too low. The decimal parts mD were then increased to 13 bit for best accuracy in computation. 5. Architecture Optic flow sensor Figure 7 shows the EMD architecture . This architecture has several important features such as the optimization of the digital filters the simplicity of design owing to the use of Intellectual Property IP cores and the added flexibility in the circuit design. Special care was taken to restrict the space taken by the digital filter implementation. Instead of implementing eight IIR digital filters in parallel - which would each require a high number of mathematical operators adders subtracters and multipliers - a single structure called the Filter Compute Unit was developed with which high speed sequential processing can be performed as shown in figure 8. This unit consists of only one multiplier one adder one Read Only Memory ROM one Random Access Memory RAM two multiplexers three registers and two binary transformation functions. The ROM contains the 17 filter coefficients obtained at a sampling frequency fS . The RAM is used to store the .
