The state-of-the-art visual simultaneous localization and mapping (V-SLAM) systems have high accuracy localization capabilities and impressive mapping effects. However, most of these systems assume that the operating environment is static, thereby limiting their application in the real dynamic world. In this paper, by fusing the information of an RGB-D camera and two encoders that are mounted on a differential-drive robot, we aim to estimate the motion of the robot and construct a static background OctoMap in both dynamic and static environments. A tightly coupled feature-based method is proposed to fuse the two types of information based on the optimization. Dynamic pixels occupied by dynamic objects are detected and culled to cope with dynamic environments. The ability to identify the dynamic pixels on both predefined and undefined dynamic objects is available, which is attributed to the combination of the CPU-based object detection method and a multiview constraint-based approach. We first construct local sub-OctoMaps by using the keyframes and then fuse the sub-OctoMaps into a full OctoMap. This submap-based approach gives the OctoMap the ability to deform, and significantly reduces the map updating time and memory costs. We evaluated the proposed system in various dynamic and static scenes. The results show that our system possesses competitive pose accuracy and high robustness, as well as the ability to construct a clean static OctoMap in dynamic scenes.
Purpose
The paper aims to develop a cownose ray-inspired robotic fish which can be propelled by oscillating and chordwise twisting pectoral fins.
Design/methodology/approach
The bionic pectoral fin which can simultaneously realize the combination of oscillating motion and chordwise twisting motion is designed based on analyzing the movement of cownose ray’s pectoral fins. The structural design and control system construction of the robotic fish are presented. Finally, a series of swimming experiments are carried out to verify the effectiveness of the design for the bionic pectoral fin.
Findings
The experimental results show that the deformation of the bionic pectoral fin can be well close to that of the cownose ray’s. The bionic pectoral fin can produce effective angle of attack, and the thrust generated can propel robotic fish effectively. Furthermore, the tests of swimming performance in the water tank show that the robotic fish can achieve a maximum forward speed of 0.43 m/s (0.94 times of body length per second) and an excellent turning maneuverability with a small radius.
Originality/value
The oscillating and pitching motion can be obtained simultaneously by the active control of chordwise twisting motion of the bionic pectoral fin, which can better imitate the movement of cownose ray’s pectoral fin. The designed bionic pectoral fin can provide an experimental platform for further study of the effect of the spanwise and chordwise flexibility on propulsion performance.
Features of fish like environmental compatibility and maneuverability have attracted bio-inspired design researchers worldwide to contemplate the practical applications of robotic fish. This paper presents a conceptual design and development of a robotic fish based on the cownose ray. We extracted essential biomimetic parameters of the cownose ray to develop reasonable simplifications of the body shape, the mechanical structure design principle of the multi-joint driving fin rays, and the motion principle. Practical motion abilities of the internal driven skeleton of the bionic prototype are calculated theoretically and compared with its natural model. Parameters affecting propulsion performances are analyzed utilizing a one-dimensional calculation method. The basic motion modes are obtained according to the analysis. Observations show that the developed robotic fish can perform bionic sinusoidal flapping movements. Positive forward propulsion forces and desired turn torques are measured on the towing tank. The maximum linear forward swimming speed of the bionic fish is 0.7 times of body length per second (BL/s). Maneuvering abilities of the pivot turn and swimming through narrow passages by rolling swim are demonstrated to confirm the design idea.
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