| The posture of the vehicle will be inevitably changed in unstructured terrain,which will lead to the deviation of gravity,loss of driving force,and even rollover in some conditions.Because active suspension can control the body posture,and has great advantages in improving riding comfort and handling stability.As a kind of active suspension,the slow active suspension is close to full active suspension in performance,and has more advantages in cost and energy consumption,so it has been widely concerned.After decades of research,the slow active suspension has achieved a lot of substantial results,but there are still some problems worth studying.Firstly,the current slow active suspension mainly refers to the hybrid slow active suspension,due to the limitation of damper,it has limitations in dealing with the posture control caused by unstructured terrain,while the series slow active suspension has advantages in dealing with large posture angles caused by unstructured terrain.Secondly,the research on series slow active suspension is less,and the modeling,model dimension reduction,and parameter uncertainty analysis need to be further studied.Finally,the current slow active suspension is basically designed for wheeled vehicles,due to the limitation of chassis structure,the trafficability of wheeled vehicles in unstructured terrain is limited.According to the above analysis,based on the theoretical analysis,model building,algorithm optimization,and controller design,a Four Wheel-Legged Vehicle(FWLV)with series slow active suspension is designed with the enhancing of posture control ability in unstructured terrain.(1)A prototype is presented.For the problem that it's not easy to get the experimental vehicle with active suspension,an experimental vehicle with independent intellectual property rights is designed firstly in this paper,then the design concept of series slow active suspension and wheel-legged structure are described,and the control principle of the actuator and driving system are analyzed.Finally,the structural strength analysis of the vehicle is carried out.(2)Inverse kinematics control of series slow active suspension is presented.Although the kinematic model ignores some characteristics of the suspension,it has certain advantages indealing with the change of posture caused by unstructured terrain.To build the kinematic model of FWLV,it's regarded as a parallel mechanism composed of multiple legs firstly,then the jacobian matrix and inverse kinematic model are derived based on D-H coordinate transformation and homogeneous differential transformation.Finally,the effectiveness of the model and algorithm is verified by simulation and experiment.(3)The dynamic model and parameter uncertainty analysis of series slow active suspension are presented.Firstly,the difficulties in building the dynamic model and the system state equation of the series slow active suspension are analyzed.Secondly,the 11 DOF dynamic model and the system state equation with 30 state variables are successfully built through matrix augmentation,model equivalence and second-order low-pass filter.Then the effectiveness of the model is verified by terrain estimation model and LQR controller.Finally,to analyze the parameter uncertainty caused by the system,a sliding mode controller is designed.The consistence of simulation results and experimental results verified the effectiveness of the proposed control strategy.(4)Model dimension reduction of series slow active suspension is presented.To avoid the high dimension of controller caused by the high degree of freedom of the model and the overload problem of the controller.Firstly,based on the idea of improved skyhook damping,the model degree of freedom of the series slow active suspension is reduced from 11 to 7,and the system state variables are also reduced from 30 to 14.Secondly,according to the low degree of freedom model,a low dimension controller is designed.Finally,the feasibility and effectiveness of the controller are validated by VCU. |
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