Joint control is crucial in the innovative applications of manipulators on fluctuating marine surface. Unlike the motion control methods of terrestrial robots, the ocean's waves exert continuous and stochastic effects on robots. We solved two problems. On the one hand, we proposed a method to use these effects to drive joint motion and save energy. On the other hand, we proposed a method to resist the effects of water disturbance for precision manipulation.

• 2-joint solar tracker utilizing wave

To address the issue of wave utilization, we propose a model-based method that enables robot joints to move to specified positions under wave action. Based on this method, we developed a wave-driven solar tracker. We established a dynamic model for the device and constructed a motion controller based on the model. To compensate for the disturbance caused by wind, we built a sliding mode observer to enhance the robustness. To our knowledge, this is the world's first method for controlling rotating joints using waves. Finally, we validated our algorithm through indoor and outdoor experiments.

Figure 1. Concept illustration and joint design of the wave-driven solar tracker.

Figure 2. Way-point tracking experiments on the water surface

• Multi-joint manipulator resisting wave

To resist the effects of waves, we propose a predictive control method. We apply this method to the scenario of a manipulator assisting a drone landing, where the robotic arm balances the end-effector under the conditions of base motion and tracks the drone to provide a stable landing platform. We propose a predictive method based on a wavelet network to generate a reference trajectory, and execute optimal joint control based on model predictive control. We validate our method through simulations and experiments.

Figure 3. Platform of manipulator-assisted drone landing.

Figure 4. Experimental validation

Selected publications:

1. Ruoyu Xu, Xiaoqiang Ji, Chongfeng Liu, Jiafan Hou, Zhongzhong Cao, and Huihuan Qian*, “Design and control of a wave-driven solar tracker”, IEEE Transactions on Automation Science and Engineering, pp. 1-13, June 14, 2022.
2. Ruoyu Xu, Xiaoqiang Ji, Hengli Liu and Huihuan Qian*, “A predictive control method for stabilizing a manipulator-assisted UAV landing platform on a disturbed USV”, 2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 8625-8632, Prague, Czech Republic, September 27 – October 1, 2021.
3. Ruoyu Xu, Hengli Liu, Chongfeng Liu, Zhenglong Sun, Tin Lun Lam, and Huihuan Qian*, “A novel solar tracker driven by waves: from idea to implementation”, 2020 International Conference on Robotics and Automation (ICRA), pp. 8209-8214, Paris, France, May 31 – August 31, 2020.