Tham khảo tài liệu 'underwater vehicles part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Dynamic Modelling and Motion Control for Underwater Vehicles with Fins 549 4 3 2 1 3 2 1 0 2 1 0 -2 1 0 -1 -2 0 -1 -2 -3 Table 1. Control rules table Generally the function of sigmoid curve is given by y e - k 31 Then the function of sigmoid curved surface is z e -k1x-k2y 32 Thus the designed control model of S surface controller is u e -k1e-k2e 33 where e and e stand for the input information error and the rate of error change which are normalized u is the control output which is the output force normalized in each freedom and k1 and k2 are the control parameters corresponding to error and rate of error change respectively. In equation 33 there are only two control parameters k1 and k2 which S surface controller need to adjust. It is important to note that S surface controller can not get the best matching whether adopting manual adjustment or adaptive adjustment. This is because that the adjustment is global and local adjustment is not available. Therefore parameter adjustment is just the approximation of the system. After all due to the complexity and uncertainty of control object any kind of approach has big approximation. Thus the optimal parameters k1 and k2 are different due to different velocities. Manual adjustment of control parameters can make the motion control of underwater vehicle meet the demand in most cases. Response is more sensitive to small deviation but vibrations easily occur when k1 and k2 are larger. Therefore the initial values of k1 and k2 we choose are generally about . If the overshoot is large we can reduce k1 and increase k2 simultaneously. By contrast if the speed of convergence is slow we can increase k1 and reduce k2 simultaneously. The ocean current and unknown disturbances can be considered as fixed disturbance force in a samlping period. Thus we can eliminate the fixed deviation by adjusting the excursion of S surface and the function of control model is u e -k1e-k2e Au 34 .
