Cable-driven parallel robots are mechanisms that control the position and attitude of an object using multiple cables. Typical cable-driven parallel robots have been studied for use on land, but not for use in water. This is because the position and attitude control of object and motion analysis become difficult underwater due to the large deformation of cables caused by fluid forces. In this paper, we propose an underwater cable-driven parallel robot consisting of multiple on-water robots and derive a dynamics model that considers the cable dynamics underwater. Then, we proposed a position and attitude control system for the suspended object based on the inverse kinematics problem for the suspended object and studied its effectiveness by simulation by using the planar two degrees-of-freedom underwater cable-driven parallel robot.

A cable-driven parallel robot (CDPR) is a mechanism that controls the position and attitude of an object using multiple cables. We propose an underwater cable-driven parallel robot (UCDPR), which is a CDPR composed of multiple surface robots. A UCDPR is a type of mobile cabledriven parallel robot (MCDPR) that is composed of multiple mobile robots and is an underwater application of MCDPR, which has been used only on land and in the air. We describe the details of the operational scenario of the UCDPR, from landing on the water to executing a task. We also simulated numerically the stabilization phase required after landing on water and the trajectory tracking control phase required for underwater exploration and other tasks. In this numerical simulation, we used a high-gain feedback controller as the trajectory tracking controller to add robustness to the control system. As a result, a trajectory tracking control was realized within a tolerance tracking error range of 10 −2 m underwater in the presence of a maximum current velocity of 0.8 m/s (≅ 1.5 knots), which is a control requirement.

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We are currently developing a mobile scaffolding device that can dodge the piers of bridges without dismantling the scaffold when moving between spans to improve efficiency and safety in bridge inspections. The mobile scaffolding device treated in this paper is split in the center of the device when it crosses the piers. In this process, the mobile scaffold is cantilevered and poses a danger to the workers on board. Therefore, we implemented horizontal holding control by wire reeling to keep the mobile scaffold horizontal. However, in this control method, the direction of motion of the mobile scaffold is only partially constrained by the wire. Thus, the device is greatly excited when an external force is applied. It is difficult to damp these oscillations in wire-reeling control. We designed a semi-active dynamic absorber for vibration control by applying the skyhook theory, a basic theory of the active suspension. When a random input that simulates the wind force was given to the mobile scaffolding device with the dynamic absorber, the vibration of the device was reduced by half compared with that of the mobile scaffolding device without the dynamic absorber.

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