Design and test of flexible chassis automatic tracking steering system

In order to develop an innovative omnidirectional non-homonymic flexible chassis(FC),the four-wheel steering control method of FC was designed by a new concept called off-centered steering(OCS)and the automatic tracking steering system was analyzed.Novelty of this wheel concept lies in the non-conventional positioning of the steering axis and wheel axis.Additionally,the steering axis of steerable wheel was motorized with an on/off electrometrical brake to overcome a hyper-motorization issue inherent to the wheel’s geometrical properties and hold the steering position.Based on the off-centered steering characteristics of FC,the Wheatstone bridge was applied in the steering control system.The bridge resistances are used to track target steering angles and the actual steering angle,respectively.The output voltage of the bridge is exploited to adjust the wheel’s speed so that steering and automatic tracking could be achieved.Experiments at different speeds,loadings,and target steering angles were conducted.Results showed that the chassis can indeed be controlled independently and its steering range is from-90°to 90°,which indicated the automatic tracking steering system was effective.The electromagnetic lock(EL)can significantly improve the stability of the chassis and reduce the vibration.Loading has no significant effect on the accuracy of the steering angle and the time it takes to complete steering tasks.The time taken to complete a forward steering task showed a linear relationship with the required angles,but was independent of rotation speed;for backward steering,time was related to both target angles and rotation speed.The results presented in this research may provide a reference for the steering control strategies of the four-wheel individual drive and four-wheel(4WID/4WIS)vehicle in the future.

Robotic Knee Tracking Control to Mimic the Intact Human Knee Profile Based on Actor-Critic Reinforcement Learning

We address a state-of-the-art reinforcement learning(RL)control approach to automatically configure robotic pros-thesis impedance parameters to enable end-to-end,continuous locomotion intended for transfemoral amputee subjects.Specifically,our actor-critic based RL provides tracking control of a robotic knee prosthesis to mimic the intact knee profile.This is a significant advance from our previous RL based automatic tuning of prosthesis control parameters which have centered on regulation control with a designer prescribed robotic knee profile as the target.In addition to presenting the tracking control algorithm based on direct heuristic dynamic programming(dHDP),we provide a control performance guarantee including the case of constrained inputs.We show that our proposed tracking control possesses several important properties,such as weight convergence of the learning networks,Bellman(sub)optimality of the cost-to-go value function and control input,and practical stability of the human-robot system.We further provide a systematic simulation of the proposed tracking control using a realistic human-robot system simulator,the OpenSim,to emulate how the dHDP enables level ground walking,walking on different terrains and at different paces.These results show that our proposed dHDP based tracking control is not only theoretically suitable,but also practically useful.

A Retrodirective Array Enabled by CMOS Chips for Two-Way Wireless Communication with Automatic Beam Tracking

This article proposes and demonstrates a retrodirective array(RDA)for two-way wireless communication with automatic beam tracking.The proposed RDA is enabled by specifically designed chips made using a domestic complementary metal-oxide semiconductor(CMOS)process.The highly integrated CMOS chip includes a receiving(Rx)chain,a transmitting(Tx)chain,and a unique tracking phaselocked loop(PLL)for the crucial conjugated phase recovery in the RDA.This article also proposes a method to reduce the beam pointing error(BPE)in a conventional RDA.To validate the above ideas simply yet without loss of generality,a 2.4 GHz RDA is demonstrated through two-way communication links between the Rx and Tx chains,and an on-chip quadrature coupler is designed to achieve a nonretrodirective signal suppression of 23 dBc.The experimental results demonstrate that the proposed RDA,which incorporates domestically manufactured low-cost 0.18 lm CMOS chips,is capable of automatically tracking beams covering±40
with a reduced BPE.Each CMOS chip in the RDA has a compact size of 4.62 mm^(2) and a low power consumption of 0.15 W.To the best of the authors’knowledge,this is the first research to demonstrate an RDA with a fully customized CMOS chip for wireless communication with automatic beam tracking。

Automatic stabilization of velocity for ultrasonic vibration system

Describes the structure of a current feedback ultrasonic generation system with such characteristic as velocity stabilization and automatic frequency tracking, discusses the velocity stabilization principle, and points out that successful frequency tracking is precondition for velocity stabilization.

Precise bearing and automatic target tracking in digital sonar

Precise bearing and Automatic Target Thacking (ATT) for moving vessels is an important thesis in passsive sonar design. Thaditionally in the analogue sonar, DOA (Direction Of Arrival) of the target is determined by the single beam steerillg directioll, which rotate some kind of compensator to steer the target. The compensator is typically made of many electronic and mechanical components. The bearing accuracy substantially depellds on the accuracy of tapped delay line and many mechanical factors. With the application of digital technique in sonar, the precise bearing and ATT technique have attracted much interests for sonar designer. For a digital sonar the multi-beam system has discrete beam direction, which distributed in space, each beam has its fixed steering direction. It is important to use them to estimate precisely DOA of target and then to track the target automatically when the target is moving. An algorithm, which can precisely estimate the value of DOA of the target, is derived in this paper. The relationship among bearing accuracy and the array aperture, signal frequency band is expressed. The expression of time-delay estimation and bearing accuracy is presented. DOA of the target can be precisely calculated by the parabolic interpolation in the neighbourhood of the main lobe of the directivity function. It is easy to implement ATT technique in real time by DSP chips. The results of system simulation show that the algorithm derived in this paper has very good performance in target tracking.

Visual detection of rice rows based on Bayesian decision theory and robust regression least squares method

Paddy field management is complicated and labor intensive.Correct row detection is important to automatically track rice rows.In this study,a novel method was proposed for accurate rice row recognition in paddy field transplanted by machine before the disappearance of row information.Firstly,Bayesian decision theory based on the minimum error was used to classify the period of collected images into three periods(T1:0-7 d;T2:7-28 d;T3:28-45 d),and resulting in the correct recognition rate was 97.03%.Moreover,secondary clustering of feature points was proposed,which can solve some problems such as row breaking and tilting.Then,the robust regression least squares method(RRLSM)for linear fitting was proposed to fit rice rows to effectively eliminate interference by outliers.Finally,a credibility analysis of connected region markers was proposed to evaluate the accuracy of fitting lines.When the threshold of credibility was set at 40%,the correct recognition rate of fitting lines was 96.32%.The result showed that the method can effectively solve the problems caused by the presence of duckweed,high-density inter-row weeds,broken rows,tilting(±60°),wind and overlap.