Lie Yu

The purpose of this paper is to apply an intelligent algorithm to conduct the torque tracking control for lower limb exoskeleton robot driven by an electro-hydraulic servo system (EHSS). The dynamics of EHSS actuating the robot are mathematically modeled with two degrees of freedom joints, and the torque control strategy is made to realize the minimization of human-machine forces. The PI controller is selected to implement this strategy, and the selection of PI gains is important for system control. Therefore, the ameliorative moth flame optimization (AMFO) algorithm is chosen to optimize the PI gains. The main idea of moth flame optimization is to mimic the evolution of a moth’s lateral positioning mechanism over time. The AMFO algorithm is capable of achieving enhanced better global and local search capabilities by adding the inertia weights to the position update formula. Moreover, the particle swarm optimization (PSO) and whale optimization algorithm (WOA) are selected to obtain comparative results. The results indicate that, when compared to the WOA-PI and PSO-PI controllers, the AMFO-PI controller gains the least amount in terms of rise time, overshoot, steady error, mean absolute error, and root mean square error.

For a high-speed permanent magnet synchronous motor supported by air foil bearings, analyzing the influence of the electromagnetic torque on the strength of the combination rotor was necessary. In this study, the electromagnetic torque was obtained using the analytical calculation and the finite element simulation. The contact interface stress analytical equation affected by the electromagnetic torque was elaborated. A three-dimensional finite element model simulating the combination rotor was constructed, and the stress calculations were performed. The strength of the combination rotor met the design requirement. It properly reflected the characteristics of the electromechanical analysis in the combination rotor. The operation experiments were realized to verify the electromagnetic performance and the strength of the combination rotor. The simulation and experimental results were significant for the electromechanical design and analysis of the combination rotor.

This paper proposed a new novel method to adaptively detect gait patterns in real time through the ground contact forces (GCFs) measured by load cell. The curve similarity model (CSM) is used to identify the division of off-ground and on-ground statuses, and differentiate gait patterns based on the detection rules. Traditionally, published threshold-based methods detect gait patterns by means of setting a fixed threshold to divide the GCFs into on-ground and off-ground statuses. However, the threshold-based methods in the literature are neither an adaptive nor a real-time approach. In this paper, the curve is composed of a series of continuous or discrete ordered GCF data points, and the CSM is built offline to obtain a training template. Then, the testing curve is compared with the training template to figure out the degree of similarity. If the computed degree of similarity is less than a given threshold, they are considered to be similar, which would lead to the division of off-ground and on-ground statuses. Finally, gait patterns could be differentiated according to the status division based on the detection rules. In order to test the detection error rate of the proposed method, a method in the literature is introduced as the reference method to obtain comparative results. The experimental results indicated that the proposed method could be used for real-time gait pattern detection, detect the gait patterns adaptively, and obtain a low error rate compared with the reference method.

A new approach is proposed to detect the real-time gait patterns adaptively through measuring the ground contact forces (GCFs) by force sensitive resistors (FSRs). Published threshold-based methods detect the gait patterns by means of setting a fixed threshold to divide the GCFs into on-ground and off-ground statuses. However, the threshold-based methods in the literature are neither an adaptive nor a real-time approach. To overcome these drawbacks, this study utilized the constant false alarm rate (CFAR) to analyze the characteristics of GCF signals. Specifically, a sliding window detector is built to record the lasting time of the curvature of the GCF signals and one complete gait cycle could be divided into three areas, such as continuous ascending area, continuous descending area and unstable area. Then, the GCF values in the unstable area are used to compute a threshold through the CFAR. Finally, the new gait pattern detection rules are proposed which include the results of the sliding window detector and the division results through the computed threshold. To verify this idea, a data acquisition board is designed to collect the GCF data from able-bodied subjects. Meanwhile, in order to test the reliability of the proposed method, five threshold-based methods in the literature are introduced as reference methods and the reliability is validated by comparing the detection results of the proposed method with those of the reference methods. Experimental results indicated that the proposed method could be used for real-time gait pattern detection, detect the gait patterns adaptively and obtain high reliabilities compared with the reference methods.

In this research, the sliding mode control is introduced to solve the dynamic analysis of rotor system supported by active magnetic bearings (AMB) with the inherently unstable, nonlinear and strong coupling characteristics. Firstly, the rigid rotor-bearing system model is built. By linearizing the magnetic of AMB about the operating point, a four-degree of freedom rotor system supported by the radial AMB is established. Furthermore, to consider the effects of the magnetic thrust bearings on the lateral vibration of the rotor, a five-degree of freedom rotor system model is presented. Secondly, the sliding mode controller of rotor system is configured. Based on the rotor system model, switching function of the sliding mode controller is designed by the quadratic regulator so that the sliding mode controller is asymptotically stable and the sliding motion has good quality. The input of the control system is designed by the exponential reaching law to satisfy the reaching condition and to reduce the buffeting in control process. Finally, the simulation results show that the rotor's quick adjusting and steady levitating is achieved and the controller presents good dynamic performance and strong robustness.

This paper presents a novel methodology for detecting the gait phase of human walking on level ground. The previous threshold method (TM) sets a threshold to divide the ground contact forces (GCFs) into on-ground and off-ground states. However, the previous methods for gait phase detection demonstrate no adaptability to different people and different walking speeds. Therefore, this paper presents a self-tuning triple threshold algorithm (STTTA) that calculates adjustable thresholds to adapt to human walking. Two force sensitive resistors (FSRs) were placed on the ball and heel to measure GCFs. Three thresholds (i.e., high-threshold, middle-threshold andlow-threshold) were used to search out the maximum and minimum GCFs for the self-adjustments of thresholds. The high-threshold was the main threshold used to divide the GCFs into on-ground and off-ground statuses. Then, the gait phases were obtained through the gait phase detection algorithm (GPDA), which provides the rules that determine calculations for STTTA. Finally, the STTTA reliability is determined by comparing the results between STTTA and Mariani method referenced as the timing analysis module (TAM) and Lopez–Meyer methods. Experimental results show that the proposed method can be used to detect gait phases in real time and obtain high reliability when compared with the previous methods in the literature. In addition, the proposed method exhibits strong adaptability to different wearers walking at different walking speeds.

Purpose: The purpose of this paper is to present a control strategy which uses two independent PID controllers to realize the hovering control for unmanned aerial systems (UASs). In addition, the aim of using two PID controller is to achieve the position control and velocity control simultaneously. Design/methodology/approach: The dynamic of the UASs is mathematically modeled. One PID controller is used for position tracking control, while the other is selected for the vertical component of velocity tracking control. Meanwhile, fuzzy logic algorithm is presented to use the actual horizontal component of velocity to compute the desired position. Findings: Based on this fuzzy logic algorithm, the control error of the horizontal component of velocity tracking control is narrowed gradually to be zero. The results show that the fuzzy logic algorithm can make the UASs hover still in the air and vertical to the ground. Social implications: The acquired results are based on simulation not experiment. Originality/value: This is the first study to use two independent PID controllers to realize stable hovering control for UAS. It is also the first to use the velocity of the UAS to calculate the desired position.

A trunnion joint is modeled as a circular plate with two types of outer boundary conditions. One is clamped supported and the other is simply supported. Symmetrical bending deflection is produced when an external force acts on the inner side of the circular plate. The governing equations of the circular plate with these two kinds of boundary conditions are solved by using finite difference method, and the axial stiffness of the circular plate is obtained according to the relationship between the external force and the bending deflection of the circular plate. In order to verify the accuracy of the finite difference method, a finite element method was also given. The effects of rotational speed and the ratio of inner radius to outer radius of the circular plate on the axial stiffness are studied. It is shown that the rotational speed can significantly affect the axial stiffness of the trunnion joint for these two cases, especially for a lower ratio of inner radius to outer radius of the circular plate. The axial stiffness increases monotonically with the increase in rotational speed. More specifically, for a lower ratio of inner radius to outer radius of the circular plate, the axial stiffness with the simply supported boundary condition at high rotational speed is more than twice as much as the case without considering the rotational speed. Correspondingly, it is more than one and a half times for the clamped supported boundary condition.

Disc-rotor has the advantages that the common continuous rotor doesn't have, but the specific structure of the disc-rotor makes it complex to compute the natural frequencies and vibration modes. It is mainly reflected in that the discs contact each other, which will bring considerable impact on the dynamic behavior of the disc-rotor. The state of contact between the discs is closely related rod preload. In the present paper the finite element model of a disc rotor is established in ANSYS FE software. Then natural frequencies under different rod preloads are calculated, and dependence of rotor natural frequency on rod preload is analyzed. After that, modes of the rotor under a specific preload are given. By analyzing the modes, some notes of the disc rotor assembly process are obtained.