Empirical Study of a Long-reach Articulated Modular Manipulator Driven by Thrusters

Robotic manipulators using thrusters for weight compensation are an active research topic due to their potential to exceed the limits of maximum length. Due to the constraints of the cubic-square law, the structure of large manipulators must be flexible, making hardware development a very difficult issue. This paper focuses on overcoming these problems by installing inertial measurement units and microcontrollers in each unit to control thrusters locally and suppress torsional deformation around roll axis of the manipulator. Control algorithms for keeping the pitch thrusters horizontally were proposed and evaluated by prototype experiments. The effectiveness of the method to achieve the desired pitch joint angle and roll attitude by three proportional integral derivative controllers was demonstrated. In addition, the prototype showed that the system can cope with wind blowing to some extent. Consequently, the prototype which is 9.3-m-long with 6 DOF was controlled its joint positions and the prototype which is 12.4-m-long with 8 DOF was floated successfully. These results surpassed the maximum length of the manipulator achieved by previous studies by about 3-m-long.