Haitao Yu

Dynamics and motion control of a two pendulums driven spherical robot

This paper deals with the dynamics and motion control of a spherical robot designed for reconnaissance and unstructured hostile environment exploration. The robot in this paper has three DOFs and two inputs, of which the nature is a nonlinear and underactuated system with nonholonomic dynamic constraints. The improved construction of two pendulums offers novel motion principle of spherical robot, which is moving simultaneously actuated by both eccentric moment and inertial moment generated by the two pendulums. Meanwhile the mobility is enhanced when the robot behaves dynamically. The emphasis is placed on the linear motion and turning in place motion control. The dynamic model of linear motion is formulated on the basis of Lagrange equation, and a smooth trajectory planning method is proposed for linear motion. A feedback controller is constructed to ensure the accurate trajectory planning. Turning in place motion is an indispensable element of omni directional locomotion which can enhance the mobility of spherical robots. The dynamic model of turning in place motion is derived on the theory of moment of momentum, and a stick-slip principle is analyzed. The two motion control methods are validated by both simulations and prototype experiments.

A CPG-based locomotion control architecture for hexapod robot

This paper proposes a novel CPG-based control architecture for hexapod walking robot. We investigate the CPG systems from the perspective of network synchronization. In this way the motion control of hexapod robot can be refined into the gait generation level and joints coordination level. On the first level, we develop a gait generator consists of CPG network in ring based on modified Van der Pol (VDP) oscillator to realize various stable gaits as well as gait transition for hexapod walking. The limit cycle behavior of VDP model is analytically studied by virtue of perturbation technique. On the second level, we address the problem of multi-DoF coordination of single leg via phase order modulation and amplitude adjustment of the neural oscillators. Consequently we propose a single-leg controller consists of a three-coupled CPG network and a linear coefficient converter to generator smooth and feasible trajectories in task space. The effectiveness of the proposed control architecture is demonstrated through simulation and real physical robot experiment.

Analysis on the Performance of the SLIP Runner with Nonlinear Spring Leg

The spring-loaded inverted pendulum(SLIP) has been widely studied in both animals and robots. Generally, the majority of the relevant theoretical studies deal with elastic leg, the linear leg length-force relationship of which is obviously conflict with the biological observations. A planar spring-mass model with a nonlinear spring leg is presented to explore the intrinsic mechanism of legged locomotion with elastic component. The leg model is formulated via decoupling the stiffness coefficient and exponent of the leg compression in order that the unified stiffness can be scaled as convex, concave as well as linear profile. The apex return map of the SLIP runner is established to investigate dynamical behavior of the fixed point. The basin of attraction and Floquet Multiplier are introduced to evaluate the self-stability and initial state sensitivity of the SLIP model with different stiffness profiles. The numerical results show that larger stiffness exponent can increase top speed of stable running and also can enlarge the size of attraction domain of the fixed point. In addition, the parameter variation is conducted to detect the effect of parameter dependency, and demonstrates that on the fixed energy level and stiffness profile, the faster running speed with larger convergence rate of the stable fixed point under small local perturbation can be achieved via decreasing the angle of attack and increasing the stiffness coefficient. The perturbation recovery test is implemented to judge the ability of the model resisting large external disturbance. The result shows that the convex stiffness performs best in enhancing the robustness of SLIP runner negotiating irregular terrain. This research sheds light on the running performance of the SLIP runner with nonlinear leg spring from a theoretical perspective, and also guides the design and control of the bio-inspired legged robot.

Enhancing Adaptability of a Legged Walking Robot with Limit-Cycle Based Local Reflex Behavior

This paper deals with the reactive behavior generation for hexapod walking inspired by insects’ robust and dexterous performance in complex environment. The single-leg controller including a coupled CPG network and linear coefficient converter is developed to yield stable and rhythmic signals for joint movement, the limit cycle behavior of which is systematically investigated with the Multi-variable Harmonic Balance (MHB) analysis. With these results, two typical local reflexes are further established. Based on the structure of the proposed single-leg controller, the elevator reflex is fulfilled via orbit attraction of limit cycles while the searching reflex is realized via limit cycle shift. The effectiveness of the proposed algorithm is confirmed through walking simulations.

Comparison of Gradeability of a Wheel-Legged Rover in Wheeled Mode and Wheel-Legged Mode.

The gradeability of a rover is important for the detection in Mars exploration mission. The traditional rovers used in former American Mars projects and Chinese Chang’e project are all wheeled rover. The gradeability of this type rover is limited by the wheel-soil interaction. The wheel-legged rover has stronger gradeability than wheeled rover because it can use more soil strength. This paper proposes the structure of a wheel-legged rover utilizing the rocker-bogie suspension, the kinematics principle and terrametrics principle of the rover. In wheel-legged mode, the traction force provided by the brake wheel is more than 1.5 times of the drawbar pull of a same size driving wheel. This paper compares the gradeability of mobile system in the wheeled mode and the wheel-legged mode when the rover climbs 20° slope, compares the maximum power of mobile system when rover climbs 20° slope in different modes, and predicts the maximum power of rover in climbing 25° slope utilizing wheel-legged mode.

Trajectory tracking control of WMRs with lateral and longitudinal slippage based on active disturbance rejection control

Abstract With the increasing application of wheeled mobile robots on soft terrains, the challenge of lateral and longitudinal slippage existing in the contact surface between the wheels and the terrain has attracted more attention. To address the difficulties caused by the lateral and longitudinal slippage, this paper proposes an improved linear active disturbance rejection control (LADRC) method for path tracking control of a six-wheeled corner steering rover. Based on the LADRC, the tracking differentiator and nonlinear state error feedback are introduced into the improved LADRC. By using the improved LADRC, the influence of disturbances in inputs can be attenuated and a higher regulating efficiency than LADRC can be achieved. The simulations validate the effectiveness of the proposed approach with a good tracking performance.

Optimal Energy Consumption for Mobile Manipulators Executing Door-Opening Task

As a substitute for humans, the mobile manipulator has become increasingly vital for on-site rescues at Nuclear Power Plants (NPPs) in recent years. The high energy efficiency of the mobile manipulator when executing specific rescue tasks is of great importance for the mobile manipulator. This paper focuses on the energy consumption of a robot executing the door-opening task, in a scenario mimicking an NPP rescue. We present an energy consumption optimization scheme to determine the optimal base position and joint motion of the manipulator. We developed a two-step procedure to solve the optimization problem, taking the quadric terms of the joint torques as the objective function. Firstly, the rotational motion of the door is parameterized by using piecewise fifth-order polynomials, and the parameters of the polynomials are optimized by minimizing the joint torques at the specified base position using the Quasi-Newton method. Second, the global optimal movement of the manipulator for executing the door-opening task is acquired by means of searching a grid for feasible base positions. Comprehensive door-opening experiments using a mobile manipulator platform were conducted. The effectiveness of the proposed method has been demonstrated by the results of physical experiments.

Low Impact Force and Energy Consumption Motion Planning for Hexapod Robot with Passive Compliant Ankles

Motion planning plays an important role in the performance optimization of legged robots. This paper presents a method to minimize the impact force and energy consumption effectively by providing an integrated strategy of motion planning subject to velocity and acceleration constraints. The parameters defined for the motion planning are computed to generate the foot trajectory. A foot–terrain interaction model and an energy-consumption model are formulated to evaluate the contact force and power consumption for statically stable gaits. The proposed method has been implemented on a hexapod robot. The acceleration of foot landing is reduced, and constant velocity control of the trunk body with passive compliant ankles is achieved for reducing the impact force and energy consumption. Extensive experiments have been carried out, and the experimental results have demonstrated the effectiveness of the proposed method in comparison with a conventional method.

Dual-SLIP model based galloping gait control for quadruped robot: A Task-space Formulation

This paper presents a novel locomotion control framework that achieves stable galloping gait for a torque-controlled quadruped robot. By analytically exploiting the stance dynamics of the Spring-Loaded Inverted Pendulum (SLIP) model, a two-layered Dual-SLIP model based Task-space Formulation (DS-TSF) is developed to control the 12-DoF quadruped robot with an active spine. On the higher layer, a dead-beat controller based on the derived Approximate Apex Return Map (AARM) with guaranteed high prediction accuracy is devised to provide desired apex state. This reference SLIP-like behavior serves as the target Center of Mass (CoM) trajectories of the fore- and hind-body of the quadruped robot. On the lower layer, a prioritized multi-task controller is further developed to enforce the dual-CoMs of the fore- and hind-body to behave following the target dynamics of two uncoupled SLIP hoppers on sagittal plane. The compatible motion control of the active spinal joint is fulfilled on the null-space of the prior task without generating confliction. The simulation results have demonstrated the effectiveness of the proposed locomotion control method.