Model Parameters Identification and Backstepping Control of Lower Limb Exoskeleton Based on Enhanced Whale Algorithm

Exoskeletons generally require accurate dynamic models to design the model-based controller conveniently under the human-robot interaction condition.However,due to unknown model parameters such as the mass,moment of inertia and mechanical size,the dynamic model of exoskeletons is difficult to construct.Hence,an enhanced whale optimization algorithm(EWOA)is proposed to identify the exoskeleton model parameters.Meanwhile,the periodic excitation trajectories are designed by finite Fourier series to input the desired position demand of exoskeletons with mechanical physical constraints.Then a backstepping controller based on the identified model is adopted to improve the human-robot wearable comfortable performance under cooperative motion.Finally,the proposed Model parameters identification and control are verified by a two-DOF exoskeletons platform.The knee joint motion achieves a steady-state response after 0.5 s.Meanwhile,the position error of hip joint response is less than 0.03 rad after 0.9 s.In addition,the steady-state human-robot interaction torque of the two joints is constrained within 15 N·m.This research proposes a whale optimization algorithm to optimize the excitation trajectory and identify model parameters.Furthermore,an enhanced mutation strategy is adopted to avoid whale evolution’s unsatisfactory local optimal value.

Robust Distributed Model Predictive Control for Formation Tracking of Nonholonomic Vehicles

Dear Editor,This letter proposes a robust distributed model predictive control(MPC) strategy for formation tracking of a group of wheeled vehicles subject to constraints and disturbances. Formation control has attracted significant interest because of its applications in searching and exploration [1], [2].

Research on Energy Efficiency Characteristics of Mining Shovel Hoisting and Slewing System Driven by Hydraulic-Electric Hybrid System

Mining shovel is a crucial piece of equipment for high-efficiency production in open-pit mining and stands as one of the largest energy consumption sources in mining.However,substantial energy waste occurs during the descent of the hoisting system or the deceleration of the slewing platform.To reduce the energy loss,an innovative hydrau-lic-electric hybrid drive system is proposed,in which a hydraulic pump/motor connected with an accumulator is added to assist the electric motor to drive the hoisting system or slewing platform,recycling kinetic and potential energy.The utilization of the kinetic and potential energy reduces the energy loss and installed power of the min-ing shovel.Meanwhile,the reliability of the mining shovel pure electric drive system also can be increased.In this paper,the hydraulic-electric hybrid driving principle is introduced,a small-scale testbed is set up to verify the feasibil-ity of the system,and a co-simulation model of the proposed system is established to clarify the system operation and energy characteristics.The test and simulation results show that,by adopting the proposed system,compared with the traditional purely electric driving system,the peak power and energy consumption of the hoisting electric motor are reduced by 36.7%and 29.7%,respectively.Similarly,the slewing electric motor experiences a significant decrease in peak power by 86.9%and a reduction in energy consumption by 59.4%.The proposed system expands the application area of the hydraulic electric hybrid drive system and provides a reference for its application in over-sized and super heavy equipment.

Study on plasma expansion model of primary discharge on spacecraft solar array

In the space plasma environment, primary discharge may occur on the solar array and evolve into a destructive sustained arc, which threatens the safe operation of the spacecraft. Based on the plasma expansion fluid theory, a new multicomponent plasma expansion model is proposed in this study, which takes into account the effects of ion species, ion number, initial discharge current, and Low Earth Orbit(LEO) plasma environment. The expansion simulation of single-component and multicomponent ions is carried out respectively, and the variations of plasma number density, expansion distance, and speed during the expansion process are obtained.Compared with the experimental results, the evolution of propagation distance and speed is closed and the error is within a reasonable range, which verifies the validity and rationality of the model. The propagation characteristics of the primary discharge on the solar array surface and the influence of the initial value on the maximum propagation distance and the propagation current peaks are investigated. This study can provide important theoretical support for the propagation and evolution of the primary discharge and the key behavior of the transition to secondary discharge on spacecraft solar array.

Multi-circular formation control with reinforced transient profiles for nonholonomic vehicles:A path-following framework

This article investigates a multi-circular path-following formation control with reinforced transient profiles for nonholonomic vehicles connected by a digraph.A multi-circular formation controller endowed with the feature of spatial-temporal decoupling is devised for a group of vehicles guided by a virtual leader evolving along an implicit path,which allows for a circumnavigation on multiple circles with an anticipant angular spacing.In addition,notice that it typically imposes a stringent time constraint on time-sensitive enclosing scenarios,hence an improved prescribed performance control(IPPC)using novel tighter behavior boundaries is presented to enhance transient capabilities with an ensured appointed-time convergence free from any overshoots.The significant merits are that coordinated circumnavigation along different circles can be realized via executing geometric and dynamic assignments independently with modified transient profiles.Furthermore,all variables existing in the entire system are analyzed to be convergent.Simulation and experimental results are provided to validate the utility of suggested solution.

Prescribed Performance Evolution Control for Quadrotor Autonomous Shipboard Landing

The shipboard landing problem for a quadrotor is addressed in this paper,where the ship trajectory tracking control issue is transformed into a stabilization control issue by building a relative position model.To guarantee both transient performance and steady-state landing error,a prescribed performance evolution control(PPEC)method is developed for the relative position control.In addition,a novel compensation system is proposed to expand the performance boundaries when the input saturation occurs and the error exceeds the predefined threshold.Considering the wind and wave on the relative position model,an adaptive sliding mode observer(ASMO)is designed for the disturbance with unknown upper bound.Based on the dynamic surface control framework,a shipboard landing controller integrating PPEC and ASMO is established for the quadrotor,and the relative position control error is guaranteed to be uniformly ultimately bounded.Simulation results have verified the feasibility and effectiveness of the proposed shipboard landing control scheme.

Overall Life Cycle Comprehensive Assessment of Pneumatic and Electric Actuator

Pneumatic actuators and electric actuators have almost been applied to all manufacturing industries. The two kinds of actuators can replace each other in most fields, such as the point to point transmission occasion and some rotating occasions. However, there are very few research results about the advantages and disadvantages of two kinds of actuators under the same working conditions so far. In this paper, a novel comprehensive assessment method, named as overall life cycle comprehensive assessment （OLCCA）, is proposed for comparison and assessment of pneumatic and electric actuators. OLCCA contains mechanical properties evaluation （MPE）, life cycle cost analysis based on users （LCCABOU） and life cycle environmental impact analysis （LCEIA） algorithm in order to solve three difficult problems： mechanical properties assessment, cost analysis and environmental impact assessment about actuators. The mechanical properties evaluation of actuators is a multi-objective optimization problem. The fuzzy data quantification and information entropy methods are combined to establish MPE algorithm of actuators. Two kinds of pneumatic actuators and electric actuators with similar bearing capacity and similar work stroke were taken for example to verify the correctness of MPE algorithm. The case study of MPE algorithm for actuators verified its correctness. LCCABOU for actuators is also set up. Considering cost complex structure of pneumatic actuators, public device cost even method （PDCEM） is firstly presented to solve cost division of public devices such as compressors, aftercooler, receivers, etc. LCCABOU method is also effective and verified by the three groups of pneumatic actuators and electric actuators. Finally, LCEIA model of actuators is established for the environmental impact assessment of actuators. LCEIA data collection method and model establishment procedure for actuators are also put forward. With Simapro 7, LCEIA comparison results of six actuators can be obtained： Fossil fuels are the major environmental factor of pneumatic and electric actuators; Environmental impact of electric actuator is large than one of pneumatic actuator under the similar mechanical properties and working conditions of pneumatic and electric actuators. The results are correct and correspond with the actual mechanical properties of actuators. This paper proposes a comprehensive evaluation method of the actuators, which can solve the critical problem that similar electromechanical products are very difficult to be compared with each other from the angle of performance, cost and environment impact.

Methods to Evaluate and Measure Power of Pneumatic System and Their Applications

Pneumatic system has been widely used throughout industry, and it consumes more than billions kW h of electricity one year all over the world. So as to improve the efficiency of pneumatic system, its power evaluation as well as measurement methods should be proposed, and their applicability should be validated. In this paper, firstly, power evaluation and measurement methods of pneumatic system were introduced for the first time. Secondly, based on the proposed methods, power distributions in pneumatic system was analyzed. Thirdly, through the analysis on pneumatic efficiencies of typical compressors and pneumatic components, the applicability of the proposed methods were validated. It can be concluded that, first of all, the proposed methods to evaluation and measurement the power of pneumatic system were efficient. Furthermore, the pneumatic power efficiencies of pneumatic system in the air production and cleaning procedure are respectively about 35%–75% and 85%–90%. Moreover, the pneumatic power efficiencies of pneumatic system in the transmission and consumption procedures are about 70%–85% and 10%–35%. And the total pneumatic power efficiency of pneumatic system is about 2%–20%, which varies largely with the system configuration. This paper provides a method to analyze and measure the power of pneumatic system, lay a foundation for the optimization and energy-saving design of pneumatic system.

Stability and Stabilization of Networked Control Systems with Bounded Packet Dropout

在这份报纸，与围住的包退学学生一起的联网的控制系统(NCS ) 的一个类的稳定性和稳定问题被调查。一条反复的途径被建议作为 Markovian 与围住的包退学学生一起为 NCS 建模跳线性系统(MJLS ) 。MJLS 的转变可能性由于网络的复杂性是部分未知的。在考虑下面的系统是更一般的，它完全用盖住系统知道并且完全未知的转变可能性作为二个空间案例。而且， sensor-to-controller 和 controller-to-actuator 包退学学生同时被考虑。为内在的系统的随机的稳定性和稳定的足够的条件经由线性矩阵不平等(LMI ) 被导出明确的表达。最后，二个解说性的例子被给表明建议结果的有效性。

An Overview of Finite/Fixed-Time Control and Its Application in Engineering Systems

The finite/fixed-time stabilization and tracking control is currently a hot field in various systems since the faster convergence can be obtained. By contrast to the asymptotic stability,the finite-time stability possesses the better control performance and disturbance rejection property. Different from the finite-time stability, the fixed-time stability has a faster convergence speed and the upper bound of the settling time can be estimated. Moreover, the convergent time does not rely on the initial information.This work aims at presenting an overview of the finite/fixed-time stabilization and tracking control and its applications in engineering systems. Firstly, several fundamental definitions on the finite/fixed-time stability are recalled. Then, the research results on the finite/fixed-time stabilization and tracking control are reviewed in detail and categorized via diverse input signal structures and engineering applications. Finally, some challenging problems needed to be solved are presented.

Parallel Dispatch:A New Paradigm of Electrical Power System Dispatch

Modern power systems are evolving into sociotechnical systems with massive complexity, whose real-time operation and dispatch go beyond human capability. Thus,the need for developing and applying new intelligent power system dispatch tools are of great practical significance. In this paper, we introduce the overall business model of power system dispatch, the top level design approach of an intelligent dispatch system, and the parallel intelligent technology with its dispatch applications. We expect that a new dispatch paradigm,namely the parallel dispatch, can be established by incorporating various intelligent technologies, especially the parallel intelligent technology, to enable secure operation of complex power grids,extend system operators' capabilities, suggest optimal dispatch strategies, and to provide decision-making recommendations according to power system operational goals.

Validation of Flight Control Law Based on LFT and Structured Singular Value

The main goal of flight clearance is to use the structured singular value （ μ ） analysis of the flight control system when some parameters in the system vary in a certain range. As the p-analysis can only be done on a linear fractional transformation （LFT） model, the first step of flight clearance is to generate the LFT model of the flight control system. In this paper, based on the introduction of basic theory of LFT and μ-analysis, an X-fighter is chosen as an example to utilize the proposed methods. In order to realize the flight clearance process automatically, a novel soRware package based on MATLAB programming language is developed. The results of simulation experiments validate the feasibility and effectiveness of the novel methods proposed in this paper.

Realization of nonlinear PID with feed-forward controller for 3-DOF flight simulator and hardware-in-the-loop simulation

As friction, intrinsic steady-state nonlinearity poses a challenging dilemma to the control system of 3-DOF （three degree of freedom） flight simulator, a novel hybrid control strategy of nonlinear PID （proportionalintegral-derivative） with additional FFC （feed-forward controller） is proposed, and the hardware-in-the-loop simulation results are also given. Based on the description of 3-DOF flight simulator, a novel nonlinear PID theory is well introduced. Then a nonlinear PID controller with additional FFC is designed. Subsequently, the loop structure of 3-DOF flight simulator is also designed. Finally, a series of hardware-in-the-loop simulation experiments are undertaken to verify the feasibility and effectiveness of the proposed nonlinear PID controller with additional FFC for 3-DOF flight simulator.

Analysis of Arc Characteristics and Flow Field in Arc Chamber of High-Voltage SF_6 Auto-Expansion Circuit Breaker

A new magnetic hydro-dynamics model for nozzle arc emphasizing the interaction of arc with PTFE （polytetrafluorethylene） vapour is established based on the conservation equations. The interruption of auto-expansion circuit breaker is simulated numerically by finite element method and the influence of PTFE vapour on the arc is analysed with this model. The results reveal that the flow field inside the arc chamber is determined by the arc current, the arcing time, the nozzle arc and the clogging of its thermal boundary. The establishment of quenching pressure relies on both SF6 gas and PTFE vapour that absorbed arc energy in the nozzle. The PTFE vapour leads to an increase in the pressure of nozzle arc obviously, and a decrease in the temperature of arc. But it enhances the temperature of arc at zero current and slows down the decreasing rate of arc temperature as the current decreases.

Investigation on the Arc Ignition Characteristics and Energy Absorption of Liquid Metal Current Limiter Based on Self-Pinch Effect

The GaInSn liquid metal current limiter based on the fluid pinch effect has broad application prospects due to its particular properties. However, the limited rated current and abil- ity of power dissipation are the critical problems for its wide application. Firstly, the temperature distribution of the liquid metal current limiter （LMCL） was obtained by experiments with a rated current of 1 kA and the arc ignition phenomenon was observed with 1.5 kA, which indicates that the rated current is mainly limited by the arc rather than the high temperature compared to the traditional switchgears. Furthermore, an improved method is proposed by adding the paralleled pure resistance, impedance or another LMCL element to protect the setup from the fault energy concentration in the setup. The problem of a slower arc voltage increasing rate can be solved by adding a paralleled impedance with suitable parameters. Finally, the current limiting properties based on the improved method were investigated and the alternating oscillating current was found between two paralleled LMCL elements owing to their deviation of arc ignition in reality.

Aerodynamic-Parameter Identification and Attitude Control of Quad-Rotor Model with CIFER and Adaptive LADRC

Current research on quadrotor modeling mainly focuses on theoretical analysis methods and experimental methods,which have problems such as weak adaptability to the environment,high test costs,and long durations.Additionally,the PID controller,which is currently widely used in quadrotors,requires improvement in anti-interference.Therefore,the aforementioned research has considerable practical significance for the modeling and controller design of quadrotors with strong coupling and nonlinear characteristics.In the present research,an aerodynamic-parameter estimation method and an adaptive attitude control method based on the linear active disturbance rejection controller(LADRC)are designed separately.First,the motion model,dynamics model,and control allocation model of the quad-rotor are established according to the aerodynamic theory and Newton-Euler equations.Next,a more accurate attitude model of the quad-rotor is obtained by using a tool called CIFER to identify the aerodynamic parameters with large uncertainties in the frequency domain.Then,an adaptive attitude decoupling controller based on the LADRC is designed to solve the problem of the poor anti-interference ability of the quad-rotor and adjust the key control parameter b0 automatically according to the change in the moment of inertia in real time.Finally,the proposed approach is verified on a semi-physical simulation platform,and it increases the tracking speed and accuracy of the controller,as well as the anti-disturbance performance and robustness of the control system.This paper proposes an effective aerodynamic-parameter identification method using CIFER and an adaptive attitude decoupling controller with a sufficient anti-interference ability.

Adaptive Consensus Quantized Control for a Class of High-Order Nonlinear Multi-Agent Systems With Input Hysteresis and Full State Constraints

For a class of high-order nonlinear multi-agent systems with input hysteresis,an adaptive consensus output-feedback quantized control scheme with full state constraints is investigated.The major properties of the proposed control scheme are:1)According to the different hysteresis input characteristics of each agent in the multi-agent system,a hysteresis quantization inverse compensator is designed to eliminate the influence of hysteresis characteristics on the system while ensuring that the quantized signal maintains the desired value.2)A barrier Lyapunov function is introduced for the first time in the hysteretic multi-agent system.By constructing state constraint control strategy for the hysteretic multi-agent system,it ensures that all the states of the system are always maintained within a predetermined range.3)The designed adaptive consensus output-feedback quantization control scheme allows the hysteretic system to have unknown parameters and unknown disturbance,and ensures that the input signal transmitted between agents is the quantization value,and the introduced quantizer is implemented under the condition that only its sector bound property is required.The stability analysis has proved that all signals of the closed-loop are semi-globally uniformly bounded.The Star Sim hardware-in-the-loop simulation certificates the effectiveness of the proposed adaptive quantized control scheme.

Algorithm Research and Realization of the Turning Control System for Heavy Transportation Vehicle

The dynamics of turning system which is a nonlinear system normally has great impact on the transportation speed of the vehicle having heavy load and large size.The dynamics of turning system depends on control algorithm and its implementation,but the existing control algorithms which having high dynamics in the application of heavy transportation vehicle are complex for realization and high hardware requirement.So,the nonlinear turning system is analyzed for improving its dynamics by researching new efficient control algorithm.The models of electromagnetic valve,hydraulic cylinder and turning mechanical part are built individually to get the open-loop model of the turning system following characteristics analyzed.According to the model,a new control algorithm for heavy transportation vehicle which combined PID with Bang-Bang control is presented.Then the close-loop model of turning system is obtained under Matlab/Simulink environment.By comparing the step response of different control algorithms in the same conditions,the new algorithm＇s validity is verified.On the basis of the analysis results,the algorithm is adopted to implement the turning control system by using CAN field bus and PLC controllers.Furthermore,the turning control system has been applied in one type of heavy transportation vehicle.It reduces the response time of turning system from seconds level to 250 ms,and the speed of heavy transportation vehicle increases from 5 km/h to 30 km/h.The application result shows that the algorithm and turning control system have met all the turning requirements.This new type of turning control algorithm proposed is simple in implementation for fast response of nonlinear and large-scale turning system of heavy transportation vehicle.

Comparison of Production-Triggering Strategies for Manufacturing Enterprises under Random Orders

Although new technologies have been deeply applied in manufacturing systems,manufacturing enterprises are still encountering difficulties in maintaining efficient and flexible production due to the random arrivals of diverse customer requirements.Fast order delivery and low inventory cost are fundamentally contradictory to each other.How to make a suitable production-triggering strategy is a critical issue for an enterprise to maintain a high level of competitiveness in a dynamic environment.In this paper,we focus on production-triggering strategies for manufacturing enterprises to satisfy randomly arriving orders and reduce inventory costs.Unified theoretical models and simulation models of different production strategies are proposed,including time-triggered strategies,event-triggered strategies,and hybrid-triggered strategies.In each model,both part-production-triggering strategies and product-assembly-triggering strategies are considered and implemented.The time-triggered models and hybrid-triggered models also consider the impact of the period on system performance.The results show that hybrid-triggered and time-triggered strategies yield faster order delivery and lower inventory costs than event-triggered strategies if the period is set appropriately.