This paper addresses the issue of developing a robust and efficient controller for a manipulator for underwater applications by proposing a terminal sliding mode control scheme along with a disturbance observer and incorporating the same for 3-RRR serial spatial manipulator to ensure finite time convergence as asymptotic convergence in undesirable in underwater tasks like positioning and tracking of a trajectory. The performance of the proposed scheme is studied using extensive numerical simulations depicting practical circumstances with external disturbances and parameter uncertainties within the system. The capability of the control scheme to overcome hydrodynamic forces and moments including added mass effects, damping effects are extensively studied and validated for the control scheme. The dynamic modelling is done using the Euler-Lagrangian approach involving the energy associated with the system. The results are presented after analyzing the trajectory tracking capabilities of the manipulator in the presence of external disturbances and model uncertainties.

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This paper presents a novel assembly sequence planning (ASP) procedure utilizing a subassembly based search algorithm (SABLS) for micro-assembly applications involving geometric and other assembly constraints. The breakout local search (BLS) algorithm is adapted to provide sequencing solutions in assemblies with no coherent solutions by converting the final assembly into subassemblies which can be assembled together. This is implemented using custom-made microparts which fit together only in a predefined fashion. Once the ASP is done, the parts are manipulated from a cluttered space to their final positions in the subassemblies using a path-planning algorithm based on rapidly exploring random tree (RRT*), a random-sampling based execution, and micromanipulation motion primitives. The entire system is demonstrated by assembling LEGO® inspired microparts into various configurations which involve subassemblies, showing the versatility of the system.