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Monday, 28 October 2013

CMAC-PID in a AUV



The first step in the implementation of a CMAC-PID was the modeling of the vehicle in Simulink. Dr. Cheng Chin (Chin et al. 2006)create a symbol library for modelling of ROVs. The library provided a predefined models that can be change by a simple script in Matlab.
Figure 62  6 DOF AUV unperturbed system
As second step in the implementation of the CMAC-PID is to implement a normal PID controller. The PID component of the system was implemented in Matlab. The acceleration wanted is calculated with a script that divide the input velocity by 8 and if the velocity wanted is equal to the platform speed the acceleration is equal to zero .A value limiter was placed at the output of the system to avoid saturation of the actuators. The tuning values for the PID components were estimated giving as result:
Kp=[16 14 24 34 34 14];
Kpi=[0.01;0;0;0.01;0.01;0.001];
Kdl=[0.002 0 0 0.001 0 0];
Kd=[1.5 0.9 1.5 7 6.2 0.1];

Figure 63 PID Implementation
The implementation of the CMAC component was by the constant call of a script at a sample time of 0.01 seconds. A CMAC was implemented by each one of the DOF’s .In the first 100 cycles is calculated the maximum and minimum data points. As second step the neural networks is started. For each cycle the weight values are adjusted. The adjustments values for the CMAC are m=5,  and  .Appendix 3 c). Figure 63 show the respond to a step input in all DoF. The respond of the PID is calibrated to the fastest answer with a minor overshoot. In rotation movement and vertical motion, the system show low overshooting and fast stabilization. In lateral motions it is notice a overshooting. However the overshooting can be solved reduce the acceleration rating of the robot. Figure 65 provide the different between CMAC-PID and a normal PID in the principal signal with overshooting. The result show a minor change on the signal and a reduction on the overshooting. If the step signal is change for a sinusoidal signal the CMAC-PID show a higher importance in the maintenance of the resonance frequency of the system over the time.
Figure 64 PID position respond to a Step Input [10,5,5,0.7,0.7,0.7]
Figure 65 CMAC-PID Implementation
Figure 66 PID(RED)vs. CMAC-PID (Brown)

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