Model Predictive Control for Wheeled L-quadruped Robots Based on Hierarchical Decoupling

doi:10.12382/bgxb.2023.0984

Abstract

Abstract:

The wheeled-quadruped hybrid robot is an innovative composite robot platform that combines the features of legged and wheeled robots, enabling three modes of movement: fast wheel motion, legged obstacle-crossing, and wheel-leg combination. A control method for wheeled-quadruped robot based on linear model predictive control (MPC) is proposed to achieve the above three maneuvering modes. The MPC-based control method employs a hierarchical framework to separate the wheel speed control from the quadruped stability control. It independently controls the wheel speeds and estimates the torques while compensating for wheel-ground disturbances in real-time. For body stability control with MPC, the control model is converted into Ax+Bu standard form using state augmentation. Gravity acceleration is used to equivalently transform the end-effector force disturbances, allowing the external force disturbances to be integrated into the dynamic model without increasing the system’s state space dimension. In the simulation and practical test on Panda-W wheeled-quadruped robot, the proposed algorithm effectively mitigates the wheel-ground disturbances during wheel-leg acceleration and deceleration, achieving stable body control and successful Trot gait locomotion on various terrains.

Key words: wheeled-quadruped robot, model predictive control, hierarchical control, wheel-legged hybird locomotion

CLC Number:

TP242.6

XING Boyang, XU Wei, LI Yufeng, ZHAO Haoyu, WANG Kang, YAN Tong. Model Predictive Control for Wheeled L-quadruped Robots Based on Hierarchical Decoupling[J]. Acta Armamentarii, 2024, 45(12): 4272-4282.

Figures/Tables 16

Fig.1 Panda-W wheeled-quadruped robot

Fig.2 Block diagram of robot control system

Fig.3 Single wheel control model

Fig.4 Force analysis diagram of sagittal plane of wheeled-quadruped robot

Fig.5 Swing leg foothold planning model

Fig.6 Simulation model of Panda-W

Table 1 Parameters of Panda-W wheeled-quadruped robot

参数	数值	参数	数值
m/kg	55	w_b/m	0.44
I_xx/(kg·m²)	0.163	h_b/m	0.49
I_yy/(kg·m²)	1.21	l₁/m	0.34
I_zz/(kg·m²)	1.36	l₂/m	0.338
l_b/m	0.66	R_wheel/m	0.187

Table 2 Parameters of controller

参数	数值	参数	数值
R	1×10^-4	$Q w x, w y, w z$	[150,150,200]
Q_x_,_y_,_z	[200,200,1500]	K₁	3
Q_ψ_,_θ_,_φ	[50,50,50]	K₂	0.3
$Q x ·, y ·, z ·$	[500,500,500]

Table 2 Parameters of controller

参数	数值	参数	数值
R	1×10^-4	$Q w x, w y, w z$	[150,150,200]
Q_x_,_y_,_z	[200,200,1500]	K₁	3
Q_ψ_,_θ_,_φ	[50,50,50]	K₂	0.3
$Q x ·, y ·, z ·$	[500,500,500]

Fig.7 Webots simulated results

Fig.8 Comparison of control effects before and after compensating for wheel hub motor traction

Fig.9 Experimental data diagram after compensating for the traction force of hub motor

Fig.10 Ground-reaction force and motor simulation data graph

Fig.11 Simulation data of robot centroid state

Fig.12 Trotting gait experiment

Fig.13 Wheel driving gait experiment

Fig.14 Wheel-legged hybrid locomotion mode experiment

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