Xuewen Rong

Research of mammal bionic quadruped robots: A review

This paper focuses on the mammal bionic quadruped robots. The main challenge in this field is how to design the highly dynamical and high payload quadruped robots. This paper firstly introduces the history of bionic quadruped robots, particularly the landmark quadruped robots. Then the state-of-the art of drive mode for quadruped robots is reviewed. Subsequently, the development trend of quadruped robots is described. Based on the state-of-the art of quadruped robots, the technical difficulties of bionic quadruped robots are briefly reviewed. And the hydraulic quadruped robot developed in Shandong University is introduced. Finally, the summary and future work of the quadruped robots is given.

The extreme learning machine learning algorithm with tunable activation function

In this paper, we propose an extreme learning machine (ELM) with tunable activation function (TAF-ELM) learning algorithm, which determines its activation functions dynamically by means of the differential evolution algorithm based on the input data. The main objective is to overcome the problem dependence of fixed slop of the activation function in ELM. We mainly considered the issue of processing of benchmark problems on function approximation and pattern classification. Compared with ELM and E-ELM learning algorithms with the same network size or compact network configuration, the proposed algorithm has improved generalization performance with good accuracy. In addition, the proposed algorithm also has very good performance in the TAF neural networks learning algorithms.

Trotting Gait Planning and Implementation for a Little Quadruped Robot

This paper presents a trotting pattern generation approach and online control strategy for a little quadruped robot. The trotting gait is scheduled based on the composite cycloid method in order to improve the stability of quadruped robot. The efficiency and performance of the proposed methods are verified by simulations and experiments by means of the little quadruped robot constructed by our laboratory. The experiment results show that the average speed of the little quadruped robot on even terrain is 0.1m/s and the proposed methods are suitable and simple in terms of controlling.

Nonlinear coupling control method for underactuated three-dimensional overhead crane systems under initial input constraints:

In this paper, we present an enhanced coupling nonlinear control method for three-dimensional overhead crane systems under initial input constraints. The proposed control method can achieve superior control performance and strong robustness with respect to system parameter variations and external disturbances. Moreover, it guarantees ‘soft’ trolley start by introducing hyperbolic tangent functions into the controller. More precisely, we enhance the coupling behaviour between the trolley movement and the payload swing by fabricating two composite signals, based on which an energy-like storage function is established. Then, a nonlinear coupling control method under initial input constraints is derived directly. Lyapunov techniques and LaSalle’s invariance theorem are successfully adopted to find the asymptotic stability solution while satisfying the initial input constraints. Strict mathematical analysis of the control scheme with initial input constraints is provided as theoretical support for the superior performance of the controller. Simulation and experimental results are conducted to show the superior performance and strong robustness of the proposed control method.

Torso motion control and toe trajectory generation of a trotting quadruped robot based on virtual model control

This article presents an intuitive approach based on virtual model control for robust quadrupedal trotting. The controller consists of two main modules: support phase virtual model control for torso motion control and flight phase virtual model control for flight toe trajectory generation. We mapped the relationship between the joint torques of support legs and the torso forces. And virtual forces are applied to the torso to regulate the attitude, height, and velocities of the torso during support phase. To unify the control law, virtual forces are also applied to flight toes to track the planned trajectories that are designed based on lateral velocity of the torso and contact signals of the legs. Moreover, state machine, terrain estimator, and the high level controller are designed to control the robot trotting. Simulations of quadruped trotting versatilely on flat ground, trotting over stairs and slops as well as the impact recovery are reported to demonstrate the effectiveness and robustness of our controller. Graphical Abstract

A Hybrid Optimization Algorithm for Extreme Learning Machine

In this paper, a learning algorithm based on particle swarm optimization method (PSO) and a novel heuristic optimization method of gravitational search algorithm (GSA) for extreme learning machine (ELM) is proposed in terms of improving the generalization performance of single hidden-layer feed-forward neural networks, which is called as PSOGSA-ELM learning algorithm. The proposed learning algorithm uses a hybrid approach of PSO and GSA to select the optimal hidden biases and input weights of ELM, and then the output weights of ELM is analytically determined by the Moore-Penrose generalized inverse. The performance of the proposed algorithm is verified by regression and classification benchmark problems and is compared with PSO–ELM, GSA–ELM, and the original ELM learning algorithms, simulation results show that the proposed algorithm performs equal to or better than the other algorithms in terms of generalization performance and has good convergence speed.

Gait-based Quadruped Robot Planar Hopping Control with Energy Planning

To improve the mobility of the quadruped robot, a planar hopping control approach is proposed based on trotting gait. With the proposed approach, three joints of the stance legs are active and the fourth leg is passive. A planar kinematic model of the supporting phase is built and the calculated positions and posture of the torso are used as feedback for motion control. The forces and torque acting at the CoM of the robot torso in the plane are fully controllable and decoupled with the control approach based on a virtual model. The planar motions on three axes are controlled independently. For the hopping control, the total energy in a hopping cycle on the vertical direction is planned according to the desired hopping height of the torsos CoM and the virtual vertical stiffness of the torso is generated using the elastic potential energy of the virtual model. We verify the approach and its robustness using simulation experiments and show the results at the end of this paper.

Road utilization adhesion coefficient real-time estimation for ASR system

The real-time estimation of road utilization adhesion coefficient is an important issue for the ASR (Anti-Slip Regulation) system of electric wheel independent drive vehicle. Firstly, the 1/4 vehicle dynamics model was built based on the LuGre tire model. Then combined with wheel angular velocity information, the exponential approach law-based sliding mode observer for the road utilization adhesion coefficient estimation was designed. And the observers asymptotic stability was proved also. Finally, at different conditions of constant target slip rate, variable target slip rate and ASR controllers of different type, the simulations of road utilization adhesion coefficient real-time estimation were done in the vehicle ASR process. The results show the effectiveness and robustness of the observer proposed.

A novel energy-coupling-based control method for double-pendulum overhead cranes with initial control force constraint

A novel energy-coupling-based control method for under-actuated double-pendulum overhead cranes with initial control force constraint is proposed in this article. The significant feature of the designed controller is its superior control performance as well as its strong robustness with respect to parameter variations and external disturbances. By incorporating a smooth hyperbolic tangent function into the control law, the proposed controller guarantees soft start of the trolley. Moreover, to improve the transient performance of the crane system, coupling behavior among the trolley movement, the hook swing, and the payload swing is enhanced by introducing a generalized payload horizontal-displacement signal. Lyapunov techniques and LaSalle’s invariance theorem are utilized to prove the stability of the designed closed-loop system. Simulation results demonstrate that the new energy-coupling control method achieves superior control performance and strong robustness over different payload masses, cable lengths, desired positions, and external disturbances with reduced initial control force.

Modeling and energy-based fuzzy controlling for underactuated overhead cranes with load transferring, lowering, and persistent external disturbances

In practice, vertical load motion is always involved in overhead cranes. In this case, the cable length turns from a constant to a variable, which may induce large amplitude load swing and make it more challenging to develop an appropriate controller. Most existing control methods for varying-cable-length cranes require either linearization or approximation to the original nonlinear dynamics; moreover, the case of external load disturbances is not fully considered. Inspired by these facts, we build the model and suggest an energy-based fuzzy control method for underactuated overhead cranes with load transferring, lowering, and persistent external disturbances. To estimate the persistent external disturbances, we construct a fuzzy disturbance observer. And a strict mathematical analysis of the control method without linearization approximation is presented, providing theoretical support for the superior performance of the proposed controller. Lyapunov techniques and LaSalle’s invariance theorem are used to demonstrate the stability of the closed-loop overhead crane system. Numerical simulation results are included to examine the effectiveness and robustness of the proposed method.