This article presents a test bed for comprehensive study of a cable-driven hyper-redundant robot in terms of mechanical design, kinematics analysis, and experimental verification. To design the hyper-redundant robot, the multiple section structure is used. Each section consists of two rotational joints, a link mechanism, and three cables. In this sense, two degrees of freedom are achieved. For kinematics analysis between the actuator space and joint space, each section of the development is treated as three spherical-prismatic-spherical chains and a universal joint chain (3-SPS-U), which results in a four-chain parallel mechanism model. In order to obtain the forward kinematics from the joint space to task space directly and easily, the coordinate frames are established by the geometrical rules rather than the traditional DenavitHartenburg (D-H) rules. To solve the problem of inverse kinematics analysis, we utilize the product of exponentials approach. Finally, a prototype of 24-degrees of freedom hyper-redundant robot with 12 sections and 36 cables is fabricated and an experiment platform is built for real-time control of the robot. Different experiments in terms of trajectories tracking test, positioning accuracy test, and payload test are conducted for the validation of both mechanical design and model development. Experiment results demonstrate that the presented hyper-redundant robot has fine position accuracy, flexibility with mean position error less than 2%, and good load capacity.
Atmospheric water vapor plays a prominent role in weather forecasting and climate change, which can be measured accurately with not only the conventional water vapor observing techniques, but also the global navigation satellite system (GNSS). However, retrieving water vapor from GNSS is mainly limited to land, in particular for Beidou global navigation satellite system (BDS) which has started to provide global service since July 2020. In this contribution, we try to investigate retrieving the real-time precipitable water vapor (PWV) based on shipborne BDS kinematic precise point positioning (PPP) solutions, and an 8-day experiment over the South China Sea is carried out. The obtained BDS zenith total delay (ZTD) and PWV values are validated by the post-processed multi-GNSS (GPS + GLONASS + Galileo + BDS) ZTD and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 PWV products, respectively. The results show that the real-time shipborne BDS ZTD estimates agree well with the post-processed multi-GNSS ZTDs, which shows a difference of approximately 2.0 cm in terms of root-mean-square (RMS) after an averaged initialization time of 43.9 mins. In addition, the real-time shipborne BDS PWV demonstrates an accuracy of 3.45 mm with respect to the ERA5 PWV products. Furthermore, observations from GPSonly system, Galileo-only system, GLONASS-only system, and multi-GNSS combination are also processed in real-time mode to derive the ZTD/PWV values. It is demonstrated that the overall performance of BDS in real-time ZTD/PWV retrieval is comparable to that of Galileo, better than that of GLONASS, but slightly worse than that of GPS. Attributing to the completion of its constellation, BDS is able to sense the atmospheric water vapor over oceans independently and contributes to the time-critical meteorological applications.
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