Adaptive Trajectory Tracking Control for Nonholonomic Wheeled Mobile Robots:A Barrier Function Sliding Mode Approach

The trajectory tracking control performance of nonholonomic wheeled mobile robots(NWMRs)is subject to nonholonomic constraints,system uncertainties,and external disturbances.This paper proposes a barrier function-based adaptive sliding mode control(BFASMC)method to provide high-precision,fast-response performance and robustness for NWMRs.Compared with the conventional adaptive sliding mode control,the proposed control strategy can guarantee that the sliding mode variables converge to a predefined neighborhood of origin with a predefined reaching time independent of the prior knowledge of the uncertainties and disturbances bounds.Another advantage of the proposed algorithm is that the control gains can be adaptively adjusted to follow the disturbances amplitudes thanks to the barrier function.The benefit is that the overestimation of control gain can be eliminated,resulting in chattering reduction.Moreover,a modified barrier function-like control gain is employed to prevent the input saturation problem due to the physical limit of the actuator.The stability analysis and comparative experiments demonstrate that the proposed BFASMC can ensure the prespecified convergence performance of the NWMR system output variables and strong robustness against uncertainties/disturbances.

A Novel Trajectory Tracking Control of AGV Based on Udwadia-Kalaba Approach

Dear Editor,This letter is about an automated guided vehicle(AGV)trajectory tracking control method based on Udwadia-Kalaba(U-K)approach.This method provides a novel,concise and explicit motion equation for constrained mechanical systems with holonomic and/or nonholonomic constraints as well as constraints that may be ideal or nonideal.In this letter.

A Novel Approach for Trajectory Tracking Control of an Under-Actuated Quad-Rotor UAV

Dear Editor,This letter presents a novel Udwadia-Kalaba(U-K)approach for the trajectory tracking control of a quad-rotor unmanned aerial vehicle(UAV).Compared to conventional control approaches,the desired trajectories are treated as trajectory tracking constraints in this approach.

硬脊膜穿破硬膜外阻滞技术在初产妇分娩镇痛中的应用效果

目的观察硬脊膜穿破硬膜外阻滞技术(DPE)对初产妇分娩镇痛的效果。方法80例足月初产妇随机分为对照组和观察组,分别给予常规硬膜外阻滞镇痛或DPE镇痛。采用视觉模拟量表(VAS)、Bromage评分量表分别评估镇痛效果、下肢运动神经阻滞程度,比较两组镇痛起效时间、镇痛泵(PCA)按压次数及并发症情况。结果观察组分娩镇痛后30 min、60 min及宫口开全时VAS评分均低于对照组(P<0.05或0.01)。与对照组比较,观察组镇痛起效时间更短,PCA按压次数更少,Bromage评分更低(P<0.01)。结论DPE可有效减轻初产妇分娩疼痛及下肢运动神经阻滞程度,起效快,安全性好。

Quantitative prediction process and evaluation method for seafloor polymetallic sulfide resources

Seafloor polymetallic sulfide resources exhibit significant development potential. In 2011, China received the exploration rights for 10,000 km2 of a polymetallic sulfides area in the Southwest Indian Ocean; China will be permitted to retain only 25% of the area in 2021. However, an exploration of seafioor hydrothermal sulfide deposits in China remains in the initial stage. According to the quantitative prediction theory and the exploration status of seafloor sulfides, this paper systematically proposes a quantitative prediction evaluation process of oceanic polymetallic sulfide resources and divides it into three stages： prediction in a large area, prediction in the prospecting region, and the verification and evaluation of targets. The first two stages of the prediction process have been employed in seafloor sulfides prospecting of the Chinese contract area. The results of stage one suggest that the Chinese contract area is located in the high posterior probability area, which indicates good prospecting potential area in the Indian Ocean. In stage two, the Chinese contract area of 48^-52~E has the highest posterior probability value, which can be selected as the reserved region for additional exploration. In stage three, the method of numerical simulation is employed to reproduce the ore-forming process of sulfides to verify the accuracy of the reserved targets obtained from the three-stage prediction. By narrowing the exploration area and gradually improving the exploration accuracy, the prediction will provide a basis for the exploration and exploitation of seafloor polymetallic sulfide resources.

Predefined-Time Sliding Mode Control with Prescribed Convergent Region

Dear editor,K1 In recent years,the finite-time and fixed-time control techniques have drawn much attention.This letter will present a new method for designing a predefined-time adaptive sliding mode controller with prescribed convergent region.More specifically,class function is used to construct the sliding function,and to achieve a real sliding mode,the function is also adopted in designing the adaptive gain without knowing the disturbance’s upper bound(DUB).Compared to the existing finite-time and fixed-time controllers,the key superiority of the proposed method is that the system can converge to a prescribed arbitrarily small region in predefined time irrespective of the initial condition.In addition,the control signal is bounded along the settling period,where the settling time instance can be estimated without conservation.

七氟醚麻醉用于小儿腹腔镜疝气修补术的有效性研究

目的观察小儿腹腔镜疝气修补术应用七氟醚麻醉的临床效果。方法选取我院2017年1月至2018年3月收治的103例腹腔镜疝气修补术患儿为研究对象,按照患儿的入院时间以及手术持续时间,划分为观察组(53例)和对照组(50例),观察组患儿接受七氟醚诱导麻醉,对照组患儿接受肌肉注射氯胺酮诱导麻醉,比较两组的麻醉效果。结果观察组患儿的入睡时间、清醒时间均显著少于对照组,差异具有统计学意义(P<0.05)。观察组患儿插管后1 min、手术开始时的心率及血压均显著低于对照组,差异有统计学意义(P<0.05)。两组患儿的指脉血氧饱和度比较,差异无统计学意义(P>0.05)。结论在患儿接受腹腔镜疝气修补术前行七氟醚诱导麻醉,可以促使患儿短时间内入睡,且患儿的血压、心率不会产生大幅度改变,有利于患儿术后早期清醒,值得临床应用推广。

A Systematic Approach for Designing Analytical Dynamics and Servo Control of Constrained Mechanical Systems

A systematic approach for designing analytical dynamics and servo control of constrained mechanical systems is proposed. Fundamental equation of constrained mechanical systems is first obtained according to Udwadia-Kalaba approach which is applicable to holonomic and nonholonomic constrained systems no matter whether they satisfy the D'Alember's principle. The performance specifications are modeled as servo constraints. Constraint-following servo control is used to realize the servo constraints. For this inverse dynamics control problem, the determination of control inputs is based on the Moore-Penrose generalized inverse to complete the specified motion. Secondorder constraints are used in the dynamics and servo control. Constraint violation suppression methods can be adopted to eliminate constraint drift in the numerical simulation. Furthermore, this proposed approach is applicable to not only fully actuated but also underactuated and redundantly actuated mechanical systems. Two-mass spring system and coordinated robot system are presented as examples for illustration. © 2014 Chinese Association of Automation.

Status of aquatic organisms resources and their environments in Yangtze River system(2017-2021)⋆

The Yangtze River is the mother river of China.To promote the aquatic ecosystem protection of the great river,the Project of Yangtze Fisheries Resources and Environment Investigation(2017-2021)supported by the Ministry of Agriculture and Rural Affairs,P.R.China carried out by 24 institutes and universities that located in the Yangtze River basin surveys the status of(1)fish species composition and spatial distribution,(2)current fish abundance,(3)endangered fishes,(4)Yangtze finless porpoise,(5)aquatic eco-environments,(6)water-level fluctuation areas,(7)capture fisheries and recreational fisheries of the Yangtze River mainstream and 10 of its main tributaries,including Yalong River,Heng River,Min River(including Dadu River),Chishui River,Tuo River,Jialing River,Wu River,Han River,Dongting Lake and Poyang Lake.The results showed that there were 443 fish species(belonging to 163 genus,37 families,and 18 orders)before 2017,but only 323 fish species(including 15 new recorded exotic species)were recorded in the project of 2017-2021.Among them,Cyprinus carpio,Carassius auratus,Hypophthalmichthys molitrix,Pelteobagrus fulvidraco,Coilia brachygnathus,Silurus asotus,Saurogobio dabryi,Ctenopharyngodon idellus,Pelteobagrus nitidus,Hemiculter leucisculus,Siniperca chuatsi,Coreius heterodon,Culter alburnus,Parabramis pekinensis,and Aristichthys nobilis were the dominant species across the whole Yangtze River system.It is estimated that there were 886 million individuals weighing 124.8 million kg,merely equivalent to 27.3%of the resources in 1950s,30.9%of the resources in 1960s,or 58.7%of the resources in 1980s.In the new list of protected fishes that recorded in the Yangtze River system,only 15 of 29 were collected in this project of 2017-2021.Psephurus gladius has been affirmed to be Extinct by International Union for Conservation of Nature(IUCN).The wild individuals of Tenualosa reevesii and Luciobrama macrocephalus have disappeared for many years and maybe have been extinct already.Acipenser dabryanus has been affirmed to be Extinct in the Wild by IUCN.The natural propagations of A.sinensis,Myxocyprinus asiaticus and Trachidermus fasciatus have been interrupted for many years.The populations of Yangtze finless porpoise in the Yangtze River mainstream,Dongting Lake and Poyang Lake have steadily rising sizes and expanding distributions in 2017-2021.Parts of them migrate from one region to another with the seasons,which would result in the fluctuation of Yangtze finless porpoise population within some regions.The conventional indicators of water quality in the Yangtze River system were good and conformed to the water quality criteria of fishery in 2017-2021.In the last 40 years,the maximum surface water area in the Yangtze River basin extended to approximately 63,360 km2,the minimum surface water area covered approximately 26,396 km2,and the seasonal water-level fluctuation areas occupied approximately 36,964 km2.Compared with 1984-2000 period,the 2001-2020 period witnessed an overall decreasing trend in the frequency of surface water occurrence within about 25,869 km2 of aquatic areas.From 1984 to 2000 period to 2001-2020 period,permanent surface water has decreased by nearly 8,750 km2.In 2017,the fishermen were mainly 40-60 years old and their educational levels were mainly lower than junior high school.In 2017,most anglers were older than 40 and used hand rod and/or sea rod.Their average catch of each time was mainly less than 1 kg.Results suggested that the fishing ban in key waters of the Yangtze River basin is not only an ecological project of aquatic ecosystem conservation,but also a livelihood project for the fisherman to embrace industrial transformation and improve their living conditions.After the implementation of the fishing ban,the fisheries resources would gradually recover,and the Yangtze finless porpoise population size would also see a steady increase.However,the endangered species would remain threatened for a long time.The degraded waterbodies and water-level fluctuation areas would be the key restrictive factors for future aquatic ecosystem recovery in the Yangtze River basin.Since this survey was carried out before the fishing ban,the current results could provide a baseline for future evaluation of the effect of the Yangtze River fishing ban.

Development of a cable-driven redundant space manipulator with large bending angle by combining quaternion joints and segmented coupled linkages mechanism

A cable-driven redundant manipulator has significant potential in confined space applications, such as environmental exploration, equipment monitoring, or maintenance. A traditional design requires 3N driving motors/cables to supply 2N degrees of freedom(DOF) movement ability.The number of motors is 1.5 times that of the joints’ DOF, increasing the hardware cost and the complexity of the kinematics, dynamics, and control. This study develops a novel redundant space manipulator with decoupled cable-driven joints and segmented linkages. It is a 1680 mm continuum manipulator with eight DOF, consisting of four segmented linkages driven by eight motors/pairs of cables. Each segment has two equivalent DOF, which are realized by four quaternion joints synchronously driven by two linkage cables. The linkage cables of adjacent joints are symmetrically decoupled and offset at 180°. This design allows equal-angle movement of all the joints of each segment. Moreover, each decoupling driving mechanism is designed based on a pulley block composed of two fixed and movable pulleys. The two movable pulleys realize the opposite but equidistant motions of the two driving cables, i.e., pulling and loosening, assuring symmetrical movements of the two driving cables of each segment. Consequently, the equivalent 2N-DOF joints are driven only by 2N motors, significantly reducing the hardware cost and simplifying the mapping relationship between the motor angle/cable length and the joint angle. Furthermore, the bending range of each segment could reach 360°, which is three times that of a traditional design. Finally, a prototype has been developed and experimented with to verify the performance of the proposed mechanism and the corresponding algorithms.

Metal-atom-doped W_(18)O_(49) nanowires for electrocatalytic oxygen evolution reaction in alkaline medium

Non-noble transition metal oxides(TMOs)are promising catalysts with improved catalytic activity and stability in oxygen evolution reaction(OER).However,the structural complexity of TMO-based electrocatalysts renders the determination of the active sites and OER mechanisms challenging.Here,we demonstrate that the OER activity of Co-doped one-dimensional W_(18)O_(49)(Co-W_(18)O_(49))is intrinsically dominated by the surface structure and electronic properties of the octahedral sites and Co-O-W bonds.Compared with RuO_(2) and W_(18)O_(49) heterogeneous electrocatalysts,Co-W_(18)O_(49) exhibits higher turnover frequency,attaining 1.97 s−1 at 500 mV overpotential.The results indicate that Co substitution contributes to the localized charge distribution of the active octahedral sites constructed by the Co-O-W bonds under OER conditions.Here,we determine the mechanism of TMOs for the OER,which may be applied to various other TMOs for OER electrocatalyst design.

Active steering control for vehicle rollover risk reduction based on slip angle estimation

In this study,a robust controller is proposed for rollover risk suppression in automatically-driven vehicles by reducing the lateral acceleration through a steer-by-wire system equipped on the vehicles.First,since the slip angle is difficult to measure directly,a sliding mode observer combining an add-on switching term with a linear observer is developed to provide more robust estimation of slip angle in the presence of system uncertainties.Second,an adaptive sliding mode control method is proposed,in which the control gain is adaptively tuned to compensate for the system uncertainties.Lastly,simulation is conducted and the results verify that the proposed estimator and controller can reduce the vehicle rollover risk efficiently and robustly.