The Application of Adaptive Backstepping Sliding Mode for Hybrid Humanoid Robot Arm Trajectory Tracking Control

This paper presents a methodology of the dynamic analysis and control for a novel hybrid humanoid robot arm. The hybrid humanoid robot arm under consideration consists of a spherical parallel manipulator (SPM) connecting two revolute pairs in series form. The dynamic model of the hybrid humanoid robot arm has been set up based on the Lie group and Lie algebra combined with the principle of virtual work, which can avoid the processing of constraint reaction and the division of logic open chains, as well as a great quantity of differential operation. Aiming at the parameter uncertainties and disturbances, an adaptive backstepping sliding mode controller is developed. Compared with PD control in trajectory tracking simulation, the results show the advantage of the controller

Clustering Denoising of 2D LiDAR Scanning in Indoor Environment Based on Keyframe Extraction

In the indoor laser simulation localization and mapping (SLAM) system, the signal emitted by the LiDAR sensor is easily affected by lights and objects with low reflectivity during the transmission process, resulting in more noise points in the laser scan. To solve the above problem, this paper proposes a clustering noise reduction method based on keyframe extraction. First, the dimension of a scan is reduced to a histogram, and the histogram is used to extract the keyframes. The scans that do not contain new environmental information are dropped. Secondly, the laser points in the keyframe are divided into different regions by the region segmentation method. Next, the points are separately clustered in different regions and it is attempted to merge the point sets from adjacent regions. This greatly reduces the dimension of clustering. Finally, the obtained clusters are filtered. The sets with the number of laser points lower than the threshold will be dropped as abnormal clusters. Different from the traditional clustering noise reduction method, the technique not only drops some unnecessary scans but also uses a region segmentation method to accelerate clustering. Therefore, it has better real-time performance and denoising effect. Experiments on the MIT dataset show that the method can improve the trajectory accuracy based on dropping a part of the scans and save a lot of time for the SLAM system. It is very friendly to mobile robots with limited computing resources

Content of Heavy Metal in the Dust of Leisure Squares and Its Health Risk Assessment—A Case Study of Yanta District in Xi’an

Taking Yanta District in Xi’an as the research object, the present study measures the contents of Cadmium (Cd), Lead (Pb), Copper (Cu), Nickel (Ni), and Chromium (Cr) in dust samples and further assesses the health risk of heavy metals intake through dust based on the assessment method of human exposure risk proposed by U.S. EPA, with an aim to investigate the content of heavy metal in the dust of leisure squares and its exposure risk. As the results indicate, the average contents of five heavy metals are obviously higher than the soil background value in Shaanxi Province. Therefore, Cd, Ni, Cu, Pb, and Cr are obviously enriched in urban surface dust in Shaanxi Province, due to the influence of human activities. In addition, it can also be found that the non-carcinogen exposure risk in children is significantly higher than that in adults with the risk values of these five heavy metals all one order of magnitude higher than those of adults. Irrespective of whether addressing the results for children or adults, the non-carcinogen exposure doses of five heavy metals are sorted as Cr > Pb > Cu > Ni > Cd. According to the present situation, for a child, the total non-carcinogenic risk values of five heavy metals have exceeded the safety limit in 11 of the 20 leisure squares in Yanta District of Xi’an. That means the leisure squares are no longer suitable for physical and recreational activities. For the five heavy metals, the average non-carcinogenic risk value of Cr is largest, and causes the largest threat to health in Yanta District, Xi’an. The carcinogenic exposure doses of the heavy metals Cr, Cd, and Ni are very low in respiratory pathways and there is no carcinogenic health risk. In general, the Cr content in dust in domestic cities is higher than that of foreign cities; however, the Pb content is much lower