Angular Tracking Error Research Articles

W-Leg Jumping Robot: Mechanical Design, Dynamical Analysis and Simulation of Jumping Dual Wheel-Leg Hybrid Robot

This study primarily focuses on design, mathematically model and simulate a novel two wheel-legged hybrid robot called W-Leg Jumping robot, which has a unique ability to overcome step-like obstacles efficiently. In general, in transformable wheel-leg robot studies, the leg and wheel structure perform their movements in an interdependent manner. However, in this study, it is aimed to design a robot in which the leg and wheel structure can move independently of each other and to develop a robot that can easily overcome obstacles on flat surfaces with the wheel mode and with the leg mode. The robot can fold its legs hidden within the wheels and deploy its two degree of freedom (DoF) legs when it detects step-like obstacles. This mechanism allows the robot to overcome an obstacle with a height of twice the radius of the robot's open/close mechanism of the legs, along with the two-dimensional kinematic and dynamic analyzes of the legs, are presented in detail within the scope of this study proportional-integral-derivative (PID) controller is designed to control the joint angles of the legs. The reference angle values to be followed according to the height of the obstacle are determined using artificial neural network (ANN). Additionally, motion simulations of the robot are conducted for four different obstacle heights (20, 30, 40, and 50 cm). As a result of the PID controller, when exceeding the highest obstacle of 50 cm, the average absolute joint angular tracking error is max. 1.8829°, average tracking error max. 0.265 s and max.

The influence of three-aircraft formation blinking jamming on the performance of ground monopulse radar

The purpose of this study is to evaluate the jamming effectiveness evaluation against monopulse radar when using a non-coherent blinking jamming model at regular intervals based on three aircraft flight trajectories. To begin, the formation trajectory is solved under various aircraft attitudes to provide the radar cross section model for three-aircraft formation flying. Following that, the jamming angle tracking error model for three-aircraft formation flying is built and coupled with the features of monopulse radar angle tracking. The effective decoy angle and other criteria are used to measure the variance in jamming performance and the efficacy of formation flying radar jamming under varying jamming power and jamming gain. Finally, using the jamming effectiveness assessment criterion, the jamming effectiveness of formation flight is calculated. The findings demonstrate that the three-aircraft formation based on time transformation jamming model can successfully induce the monopulse radar angular tracking error, enhance it to 1.54 times, and stabilize the jamming effectiveness at 0.84, and it also has a relatively good jamming effect under straight flight trajectory and circular flight trajectory. Our jamming strategy will contribute to the design of electronic countermeasures, of which the findings of this research have practical significance for the application of new jamming styles.

Adaptive Robust Servo Control for Vertical Electric Stabilization System of Tank and Experimental Validation

A tracking stability control problem for the vertical electric stabilization system of moving tank based on adaptive robust servo control is addressed. This paper mainly focuses on two types of possibly fast time-varying but bounded uncertainty within the vertical electric stabilization system: model parameter uncertainty and uncertain nonlinearity. First, the vertical electric stabilization system is constructed as an uncertain nonlinear dynamic system that can reflect the practical mechanics transfer process of the system. Second, the dynamical equation in the form of state space is established by designing the angular tracking error. Third, the comprehensive parameter of system uncertainty is designed to estimate the most conservative effects of uncertainty. Finally, an adaptive robust servo control which can effectively handle the combined effects of complex nonlinearity and uncertainty is proposed. The feasibility of the proposed control strategy under the practical physical condition is validated through the tests on the experimental platform. This paper pioneers the introduction of the internal nonlinearity and uncertainty of the vertical electric stabilization system into the settlement of the tracking stability control problem, and validates the advanced servo control strategy through experiment for the first time.

Vibration Control for Flexible Manipulators With Event-Triggering Mechanism and Actuator Failures.

This article focuses on flexible single-link manipulators (FSLMs) under boundary control and in-domain control. The actuators of the system include the dc motor at the end of the joint and m piezoelectric controllers installed at the flexible link, which is regarded as an Euler-Bernoulli beam. The problem of the infinite number of actuator failures, including the partial loss of the effectiveness and total loss of effectiveness, is solved by the adaptive compensation method. By introducing the relative threshold strategy, the event-triggered control (ETC) scheme is proposed to achieve angle regulation and vibration suppression while reducing the communication burden between the controllers and the actuators. The Lyapunov direct method is utilized to prove that the system is uniformly ultimately bounded and both the angular tracking error and elastic displacement converge to a neighborhood of zero. Numerical simulation results are provided to demonstrate the effectiveness of the proposed control law.

Exoskeleton for ankle joint flexion/extension rehabilitation

This work presents the modelling, design, construction, and control of an exoskeleton for ankle joint flexion/extension rehabilitation. The dynamic model of the ankle flexion/extension is obtained through Euler-Lagrange formulation and is built in Simulink of MATLAB using the non-linear differential equation derived from the dynamic analysis. An angular displacement feedback PID controller, representing the human neuromusculoskeletal control, is implemented in the dynamic model to estimate the joint torque required during ankle movements. Simulations are carried out in the model for the ankle flexion/extension range of motion (ROM), and the results are used to select the most suitable actuators for the exoskeleton. The ankle rehabilitation exoskeleton is designed in SolidWorks CAD software, built through 3D printing in polylactic acid (PLA), powered by two on-board servomotors that deliver together a maximum continuous torque of 22 [kg cm], and controlled by an Arduino board that establishes Bluetooth communication with a mobile app developed in MIT App Inventor for programming the parameters of the rehabilitation therapies. The result of this work is a lightweight ankle exoskeleton, with a total mass of 0.85 [kg] including actuators (servomotors) and electronics (microcontroller and batteries), which can be used in telerehabilitation practices guaranteeing angular displacement tracking errors under 10%.

Mechanical Design and Control System Development of a Rehabilitation Robotic System for Walking With Arm Swing.

Background: Interlimb neural coupling implies that arm swing should be included during gait training to improve rehabilitation outcomes. We previously developed several systems for production of walking with arm swing, but the reaction forces on the foot sole during usage of the systems were not satisfactory and there was potential to improve control system performance. This work aimed to design and technically evaluate a novel system for producing walking with synchronised arm and leg movement and with dynamic force loading on the foot soles.Methods: The robotic system included a passive curved treadmill and a trunk frame, upon which the rigs for the upper and lower limbs were mounted. Ten actuators and servocontrollers with EtherCAT communication protocol controlled the bilateral shoulder, elbow, hip, knee and ankle joints. Impedance control algorithms were developed and ran in an industrial PC. Flexible pressure sensors recorded the plantar forces on the foot soles. The criteria of implementation and responsiveness were used to formally evaluate the technical feasibility of the system.Results: Using impedance algorithms, the system produced synchronous walking with arm swing on the curved treadmill, with mean RMS angular tracking error <2° in the 10 joint profiles. The foot trajectories relative to the hip presented similar shapes to those during normal gait, with mean RMS displacement error <1.5 cm. A force pattern that started at the heel and finished at the forefoot was observed during walking using the system, which was similar to the pattern from overground walking.Conclusion: The robotic system produced walking-like kinematics in the 10 joints and in the foot trajectories. Integrated with the curved treadmill, the system also produced walking-like force patterns on the foot soles. The system is considered feasible as far as implementation and responsiveness are concerned. Future work will focus on improvement of the mechanical system for future clinical application.

Event-triggered boundary control of a flexible manipulator with uncertain end load

In this study, we consider the event-triggered boundary control problem of a single-link flexible manipulator with uncertain end load. The flexible manipulator is modelled by partial differential equations (PDEs). Based on the PDE model, an event-triggered control strategy is proposed to achieve angular position tracking and vibration elimination, while alleviating the communication burden of the signal transmission between controller and actuator. The relative threshold strategy used in triggering event mechanism can adjust the update interval according to the size of the control input. The designed adaptive law with projection mapping operator can deal with undertain end load. The proposed control scheme can guarantee that all signals in the closed-loop system are uniformly ultimately bounded, and the angular tracking error and vibration converge to small zero neighbourhoods by reasonable selection of design parameters. Moreover, the Zeno phenomenon is precluded. Numerical simulation results elucidate the effectiveness of the designed control strategy.

External Torque Estimation Using Higher Order Sliding-Mode Observer for Robot Manipulators

Online monitoring of external torque/force is receiving much attention with the increasing demand in industries, where robot manipulators are required to cooperate with humans, assemble product parts or perform certain tasks that involve the interaction with fragile objects. Estimation of external torque when the robot manipulator interacts with the external environment is investigated in this article. A higher order sliding-mode-based observer is designed to estimate the external torque online against nonlinear friction. Moreover, a Luenberger observer is designed to stabilize the general momenta error dynamics by using sum of squares programming. Lyapunov analysis is considered to demonstrate the stability of an overall system and the convergence of angular position tracking errors. Simulation as well as experimental results using 7-DOF Sawyer robot under various practical scenarios demonstrate the effectiveness of the proposed scheme.

Event-triggered boundary quantization control for flexible manipulator based on partial differential equations dynamic model

In this paper, we consider boundary control for a single-link flexible manipulator system described by partial differential equations (PDEs). Existing researches on controller design rarely consider the problem of communication capacity constrains during signal transmission. To deal with this problem, an adaptive control is designed to achieve the input quantization by using the random quantizer. Besides, a triggering event is addressed on the basis of relative threshold strategy for relieving communication load between controller and actuator. The proposed scheme is able to ensure that all closed-loop signals are globally uniformly bounded, and the angular tracking error and vibration converge to a residual set. Simulation results are presented to illustrate the effectiveness of the proposed scheme.

High Performance of an Adaptive Sliding Mode Controller under Varying Loads for Lifting-Type Autonomous Grounded Robot

To work in shared space with humans, autonomous systems must carry unknown loads in predefined missions. With the conventional control scheme, the grounded robot would suffer unstable motion and imprecise tracking performance. To overcome these challenges, in this paper, a novel controller using an adaptive sliding mode for autonomous grounded robots (AGR) is proposed. This control strategy takes into consideration uncertain characteristics, varying loads, and external disturbances. To analyze the tracking performance precisely, the overall error of motion system is decoupled into two subsystems where the second-order system is related to the angular tracking error and the third-order system is associated with the linear one. Initially, the dynamics model of the grounded robot is established containing different elements of nonlinear forces in order to address the technical problems. Then, the system state equation of the autonomous system is mentioned to indicate the theoretical characteristics. Based on the proposed controller, the stability of the system is validated by the Lyapunov theorem. From the results of numerical tests, three practical situations consisting of separately linear and circular trajectories with varying loads and an S-curve trajectory of a working map are suggested. The tracking performance validates that the proposed control scheme is, in various scenarios, robust, effective, and feasible. From these superior outcomes, it can be determined obviously the property of our works in accommodating the variations of cargo from applications in distribution centers, material transportation, or handling equipment.

Automated three-dimensional tracking of the left ventricular myocardium in time-resolved and dose-modulated cardiac CT images using deformable image registration

BackgroundAssessment of myocardial deformation from time-resolved cardiac computed tomography (4D CT) would augment the already available functional information from such an examination without incurring any additional costs. A deformable image registration (DIR) based approach is proposed to allow fast and automatic myocardial tracking in clinical 4D CT images. MethodsLeft ventricular myocardial tissue displacement through a cardiac cycle was tracked using a B-spline transformation based DIR. Gradient of such displacements allowed Lagrangian strain estimation with respect to end-diastole in clinical 4D CT data from ten subjects with suspected coronary artery disease. Dice similarity coefficient (DSC), point-to-curve error (PTC), and tracking error were used to assess the tracking accuracy. Wilcoxon signed rank test provided significance of tracking errors. Topology preservation was verified using Jacobian of the deformation. Reliability of estimated strains and torsion (normalized twist angle) was tested in subjects with normal function by comparing them with normal strain in the literature. ResultsComparison with manual tracking showed high accuracy (DSC: 0.99±0.05; PTC: 0.56mm±0.47 mm) and resulted in determinant(Jacobian)>0 for all subjects, indicating preservation of topology. Average radial (0.13 mm), angular (0.64) and longitudinal (0.10 mm) tracking errors for the entire cohort were not significant (p > 0.9). For patients with normal function, average strain [circumferential, radial, longitudinal] and peak torsion estimates were: [-23.5%, 31.1%, −17.2%] and 7.22°, respectively. These estimates were in conformity with the reported normal ranges in the existing literature. ConclusionsAccurate wall deformation tracking and subsequent strain estimation are feasible with the proposed method using only routine time-resolved 3D cardiac CT.

Direct tracking error characterization on a single-axis solar tracker

The solar trackers are devices used to orientate solar concentrating systems in order to increase the focusing of the solar radiation on a receiver. A solar concentrator with a medium or high concentration ratio needs to be orientated correctly by an accurate solar tracking mechanism to avoid losing the sunrays out from the receiver. Hence, to obtain an appropriate operation, it is important to know the accuracy of a solar tracker in regard to the required precision of the concentrator in order to maximize the collector optical efficiency. A procedure for the characterization of the accuracy of a solar tracker is presented for a single-axis solar tracker. More precisely, this study focuses on the estimation of the positioning angle error of a parabolic trough collector using a direct procedure. A testing procedure, adapted from the International standard IEC 62817 for photovoltaic trackers, was defined. The results show that the angular tracking error was within ±0.4° for this tracker. The optical losses due to the tracking were calculated using the longitudinal incidence angle modifier obtained by ray-tracing simulation. The acceptance angles for various transversal angles were analyzed, and the average optical loss, due to the tracking, was 0.317% during the whole testing campaign. The procedure presented in this work showed that the tracker precision was adequate for the requirements of the analyzed optical system.

Intelligent humanoid mobile robot with embedded control and stereo visual feedback

Generally, an intelligent humanoid robot system should have dual arms, mobile ability and stereo vision for establishing the interactive capability in unknown environment. Stereo vision system detects unknown objects or obstacles from their visual range and estimates 3D coordinates in a working environment. Dual arms and mobile platform are employed to approach the detected object and execute interaction based on visual servo information. Here a wheel-based 10 DOF dual arms mobile robot with FPGA hardware control structure and a Digital signal processor (DSP) based CMOS stereo vision system was designed and built to construct an distributed embedded low cost visual guided intelligent robotic system. The intelligent fuzzy sliding mode control strategy was employed to design the robot arm and platform motion control system. The experimental results show that the proposed stereo vision algorithm has good recognition ability and accuracy. Each joint angular tracking error of humanoid robot can keep within 0.05° by using distributed FSMC controller.

Robust attitude controller design for miniature quadrotors

SummaryThis paper addresses the robust attitude control problem of miniature quadrotors. A simplified linear dynamical model is obtained for each attitude angle, whereas nonlinear dynamics, interaxis coupling, parameter perturbations, and external disturbances are considered as uncertainties. For each channel, a linear time‐invariant and decoupled robust controller are proposed based on a linear reduced‐order observer and a robust compensator. The observer is applied to estimate the angular velocities, and the robust compensator is introduced for reducing the effects of uncertainties. It is proven that the estimation errors of angular velocities and angular tracking errors can converge to the given neighborhood of the origin in a finite time. Experimental results on the miniature quadrotor are presented to verify the effectiveness of the proposed control approach. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Optical losses due to tracking error estimation for a low concentrating solar collector

The determination of the accuracy of a solar tracker used in domestic hot water solar collectors is not yet standardized. However, while using optical concentration devices, it is important to use a solar tracker with adequate precision with regard to the specific optical concentration factor. Otherwise, the concentrator would sustain high optical losses due to the inadequate focusing of the solar radiation onto its receiver, despite having a good quality.This study is focused on the estimation of long-term optical losses due to the tracking error of a low-temperature collector using low-concentration optics. For this purpose, a testing procedure for the incidence angle modifier on the tracking plane is proposed to determinate the acceptance angle of its concentrator even with different longitudinal incidence angles along the focal line plane. Then, the impact of maximum tracking error angle upon the optical efficiency has been determined. Finally, the calculation of the long-term optical error due to the tracking errors, using the design angular tracking error declared by the manufacturer, is carried out.The maximum tracking error calculated for this collector imply an optical loss of about 8.5%, which is high, but the average long-term optical loss calculated for one year was about 1%, which is reasonable for such collectors used for domestic hot water.

Simulations of reflected sun beam traces over a target plane for an azimuth–elevation tracking heliostat with fixed geometric error sources

For a heliostat with geometric errors, the reflected central solar ray from the mirror surface center forms a curved error trace on the target plane during the day rather than staying fixed on one target point. A general azimuth–elevation tracking angle formula has been developed for a heliostat with a mirror-pivot offset and other typical geometric errors. This tracking angle formula is re-rewritten here as a series of easily solved expressions. This azimuth–elevation tracking angle formula is then used in a new complete geometric model of the sun-beam tracking errors for an azimuth–elevation tracking heliostat to simulate the sun beam tracking error trace on the target plane for a heliostat with fixed geometric errors. Here, the analysis is for a point sun and a point heliostat (or the heliostat considered as a small optical flat). The mirror surface center is defined as the orthogonal projection of the heliostat pivot on the mirror surface plane. The reflected sun-beam centre in the target plane is defined as the intersection of the mirror-surface-centre reflected central solar ray with the target plane. Due to a position tracking error in the target plane depending on the position and the orientation of the specific target plane, the position tracking error is further converted to the angular tracking error in the reflection direction to facilitate evaluation of the heliostat tracking performance. Simulations for the artificial #78 heliostat in the Beijing solar tower system on June 21st are shown to illustrate this heliostat tracking error model. This heliostat tracking error model can be used to reveal the effect of various geometrical errors in pedestal tilt etc. on the location of the beam at the target, and thus is useful in setting limits on the various geometrical errors. Essentially this paper allows one to estimate the offset of the reflected solar beam centre due to specific geometrical tracking errors, once the beam centre is computed by some other means. It also allows one to determine a limit on each error or set of errors which are allowable for a given purpose.

Guidance system for agricultural tractor with four wheel steering

In a typical automatic guidance system for agricultural machines, the guidance system controls only one degree of freedom; either the steering angle of the front wheels of the tractor or other steering equipment is used for steering. In a tractor with the multiple degrees of freedom, like four wheel steering, the guidance system may use both the degrees of freedom for path tracking. However, the implement connected has to support the additional degrees of freedom; otherwise kinematic constraints are addressed. This paper presents a path tracking algorithm for four wheel steered agricultural tractor that is designed to be autonomous. The path tracking algorithm utilizes the kinematic and dynamical model of the vehicle, dynamic prediction and linear control laws to steer both front and rear axles of the tractor. The kinematic model is used to separate the two-times-time control problem into two single-input single-output problems. Conventional linear controllers are used for feedback control together with feedforward part. The guidance system uses real time kinematic GPS receiver for global positioning and additional sensors to measure the attitude of the vehicle. The developed path tracking system was tested in an agricultural field with a mounted seeder; by sowing 2.4 ha winter wheat. The results show that in straight swaths the lateral tracking error was less than 0.05m and the angular tracking error less than 1 degree. The results show also that during the field experiment, the GPS positioning signal was within the quality limits 15% of time that caused number of interrupts for continuous autonomous drive. The longest continous period of valid signal was eighteen minutes while the average of continuous driving was five minutes.

Study on Autopilot Dynamics with Robust Guidance Law and Terminal Constraint in Mechanical Engineering

A new nonlinear robust guidance law was proposed by considering autopilot dynamics. Firstly, the mathematic model was built according to relationship between target and missile in vertical plane, by introducing the one-order dynamics of autopilot in Mechanical Engineering. Secondly, the nonlinear terminal guidance was obtained by applying the H∞ control theory under the performance index of minimizing the terminal angular constraint tracking error and control energy, and the asymptotic stability of guidance system was strictly proven by Lyapunov stability theory avoiding the estimation of the time-to-go. Finally, an illustrative example was given to show that the guidance law was more robust and both the impact angle and guidance precision were met in the case of no any target information.

四象限探测器角跟踪误差对激光制导的影响

四象限探测器角跟踪误差对激光制导的影响

SLIDING MODE CONTROL FOR THE PATH FOLLOWING OF AN UNMANNED AIRSHIP

Project AURORA aims at the development of unmanned robotic airships capable of autonomous flight for aerial inspection and environmental monitoring missions. In this article the authors present the design of two MIMO Sliding Mode Controllers for the guidance and navigation system of the AURORA airship (for the longitudinal and lateral modes). The path tracking strategy minimizes the angular and distance tracking errors with respect to a given reference trajectory. The bounded stability of the system is proved, and the results are illustrated through a simulation example where the airship is submitted to a large airspeed variation.