Anti-Disturbance Direct Yaw Moment Control of a Four-Wheeled Autonomous Mobile Robot

Abstract

Profiting from its remarkable maneuverability and efficiency, the four-wheeled autonomous mobile robot (FAMR) is appealing for intelligent manufacturing and automation applications. However, the suppression of unknown disturbances and system uncertainties remains a challenge for formulating a precise trajectory-tracking control scheme. This paper achieves the anti-disturbance direct yaw moment control of a developed FAMR by proposing a robust super-twisting sliding mode controller (RSSMC) to enhance the dynamic tracking and disturbance rejection property simultaneously. One of the major contributions is that the presented RSSMC method is constructed with a novel reaching law to eliminate the matched perturbations and time-varying lumped disturbances. As another distinguishing feature, this method is capable of driving the resultant FAMR trajectory into a bounded switching region and maintaining it therein for subsequent periods in finite time. To guarantee the closed-loop stability and finite-time convergence, new sufficient conditions for specifying the variable gains are determined utilizing Lyapunov functions. Finally, under the direct yaw moment control framework, simulation experiments of a developed FAMR system are offered to verify the practicability of the RSSMC scheme.

Decoupled Fractional Supertwisting Stabilization of Interconnected Mobile Robot Under Harsh Terrain Conditions

“…1) The characteristics of the considered terrain conditions that typically occur in industrial applications include: (1) The uneven ground will disarrange the driving or actuating forces of the FOMR, thus resulting in insufficient accuracy or even leading to unstable behaviors; and (2) Oiled terrain may cause wheel slip and lateral sway, failing to generate sufficient yaw moment. Given that the harsh terrain conditions will harm the system tracking performance or even results in unstable dynamics, this paper especially attempts to achieve a stable and accurate decoupled control of the FOMR, which ensures strong robustness against harsh terrain conditions in two ways: (1) With fractional super-twisting switching law, an enhanced FST-SMC is designed to ensure the nominal tracking performance without to gain overestimation or undesirable chattering (cf., [31], [35]); and (2) An MFNN-based unbiased fuzzy estimator is designed to actively compensate for the lumped disturbances, which differs from the traditional decoupling methods [23]. Given this context, the inevitable disturbances or uncertainties caused by nonideal modeling or linearization can be well addressed comprehensively.…”

“…The lateral dynamic model of the concerned FOMR system is a nonlinear MIMO system with interconnected states. In the yaw plane, the four-wheel dynamics are denoted as [31] ( sin cos ) ( sin cos )…”

“…Then, the dynamic control problem of the FOMR concerned here is transferred as the DYMC issue to achieve robust stabilization control. Consequently, the objective of this paper is to propose a decoupled FST-SMC method that will make the DYMC output states accurately track the desired trajectories (or a constructed reference model [31]). This will be realized by designing (i) an inverse-system decoupling scheme to achieve a pseudo linear composition system; and (ii) an FST-SMC law to address the active anti-disturbance issue of the decoupled FOMR system.…”

“…To ensure state convergence, the control gains of SMC solutions normally must satisfy specific conditions relating to the upper boundaries or the derivatives of the lumped disturbances. For instance, in [31], a super-twisting SMC method was used to handle the unknown disturbances. However, the mentioned information may be unavailable in the industrial environment.…”

“…2) A modified FST-SMC is proposed to ensure that each subsystem is driven into the constructed sliding manifold. Different from the traditional SMC schemes [31], [35], a new fractional super-twisting switching law is designed to mitigate the undesirable chattering without acquiring the upper boundary of the disturbances or related derivatives. Therefore, the gain overestimation can be well addressed.…”