Abstract
In order to avoid motor saturation in turning maneuvers, an iterative Lame-trajectory planning scheme is proposed to generate a smooth curvature-bounded transition trajectory for a differential-driving wheeled mobile robot (DWMR) switching from one straight path to another. The scheme consists of Lamecurve blending, inverse-kinematics computation, peak-torque positioning and torque-saturation avoidance. Firstly, a Lame-curve blending procedure based on affine transformations, is formulated to generate a smooth G2-continuous transition trajectory for connecting two straight paths. Secondly, the platform twist is calculated according to the curvature of the Lame-curve trajectory, then transformed into the actuated-joint rates by means of the inverse-kinematics model. Thirdly, a peak-torque positioning technique is developed to estimate the peak torques of the driving wheels when the DWMR tracks the trajectory, by combining the computed-torque method and the inverse-dynamics model. Finally, an iterative r-step saturation-avoidance prediction planning strategy is devised to suppress the peak motor torques, by means of two torque limitation schemes via adjusting trajectory curvature and robot speed. The simulation results show that, compared with the conventional planning techniques for circular arcs, our trajectory planning scheme can generate a smooth saturation-free transition trajectory with feasible curvature and traveling speed. The scheme is significantly beneficial for trajectory tracking under finite actuation torque in turning maneuvers, thereby preventing any possible path deviation caused by insufficient torque.
Highlights
Automated guided vehicles (AGVs) have been typical industrial mobile robots, used for repeated transportation tasks in factories for decades [1]–[3]
Schemes for actuator-saturation avoidance in mobile robots are mainly oriented to torque-bounded controller design or curvature-bounded trajectory planning
As the causes of actuator saturation are not always known or predictable, many constrained control strategies have been used to cope with external disturbances, model nonlinearity and parameter uncertainty
Summary
Automated guided vehicles (AGVs) have been typical industrial mobile robots, used for repeated transportation tasks in factories for decades [1]–[3]. B. METHODOLOGY OVERVIEW In order to avoid motor saturation in turning maneuvers from one straight path to another, an iterative Lamé-trajectory planning scheme is proposed for mobile robots. This means that before the robot approaches the intersection of the two straight paths, the iterative planning scheme has been already used to predict the trajectory curvature and motor torques This is done for each upcoming initial point of curve blending in turning maneuvers.
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