MiResolved Acceleration Control for Underwater Vehicle-Manipulator Systems: Continuous and Discrete Time Approach

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Underwater robots, especially Underwater Vehicle-Manipulator Systems (UVMS), are expected to have important roles in ocean exploration (Yuh, 1995). Many studies about dynamics and control of UVMS have been reported (Maheshi et al., 1991; McMillan et al., 1995; McLain et al., 1996; Tarn et al., 1996; Antonelli & Chiaverini, 1998; McLain et al., 1998; Antonelli et al., 2000; Sarkar & Podder, 2001). However, there are only a few experimental studies. Most of the control methods of UVMS have been proposed based on the methods of Autonomous Underwater Vehicles. In these control methods, the desired accelerations and velocities of the end-tip of the manipulator are transformed to the desired manipulator’s joint accelerations and velocities only use of the kinematic relation, and the computed torque method with joint angle and angular velocity feedbacks are utilized. In other words, the control methods use errors consisting of task-space signals of vehicle and joint-space signals of manipulator. Therefore, the control performance of the end-effector depends on the vehicle’s control performance. We have proposed continuous-time and discrete-time Resolved Acceleration Control (RAC) methods for UVMS (Yamada & Sagara, 2002; Sagara, 2003; Sagara et al., 2004; Sagara et al., 2006; Yatoh & Sagara, 2007; Yatoh & Sagara, 2008). In our proposed methods, the desired joint values are obtained by kinematic and momentum equations with feedback of task-space signals. From the viewpoint of underwater robot control, parameters and coefficients of hydrodynamic models are generally used as constant values that depend on the shape of the robots (Fossen, 1994). Our proposed methods described above can reduce the influence of the modelling errors of hydrodynamics by position and velocity feedbacks. The effectiveness of the RAC methods has been demonstrated by using a floating underwater robot with vertical planar 2-link manipulator shown in Figure 1. In this chapter, our proposed continuous-time and discrete-time RAC methods are described and the both experimental results using a 2-link underwater robot are shown. First, we explain about a continuous-time RAC method and show that the RAC method has good control performance in comparison with a computed torque method. Next, to obtain higher control performance, we introduce a continuous-time RAC method with disturbance compensation. In practical systems digital computers are utilized for controllers, but there is no discrete-time control method for UVMS except our proposed methods. Then, we address