http://www.seas.ucla.edu/coopcontrol/papers/D'Andrea_NearOptical_trajectory.pdf

Near-optimal dynamic trajectory generation and control of an omnidirectional vehicle

A dynamic model is presented for omnidirectional wheeled mobile robots, including wheel/motion surface slip. We derive the dynamics model, experimentally measure friction coefficients, and measure the force to cause slip (to validate our friction model). Dynamic simulation examples are presented to demonstrate omnidirectional motion with slip. After developing an improved friction model, compared to our initial model, the simulation results agree well with experimentally-measured trajectory data with slip. Initially, we thought that only high robot velocity and acceleration governed the resulting slipping motion. However, we learned that the rigid material existing in the discontinuities between omnidirectional wheel rollers plays an equally important role in determining omnidirectional mobile robot dynamic slip motion, even at low rates and accelerations.

Dynamic model with slip for wheeled omnidirectional robots

Omni-directional mobile robot controller based on trajectory linearization

This paper presents a reduced-order extended state observer (ESO) based sliding mode control scheme for friction compensation of a three-wheeled omnidirectional mobile robot. Compared with previous works, the proposed control approach is attractive from an implementation point of view. It does not require any explicit friction model, with quite low computation cost. First, a dynamic model with unknown friction forces is given. Then, the controller is designed, consisting of two parts. One part of the control effort is to compensate the friction effects, which are estimated by a reduced-order ESO without using any explicit friction model. The inverse of inertia matrix is also avoided in the proposed reduced-order ESO. The other part of the control effort is designed based on a second-order sliding mode technique known as super-twisting algorithm, in presence of parameter uncertainties. In addition, stability analysis of the designed control system is presented. Extensive experiments are conducted to verify the effectiveness and robustness of the proposed control design in compensating different friction effects.

Extended State Observer-Based Sliding Mode Control of an Omnidirectional Mobile Robot With Friction Compensation

To maximize total operating time, an online minimum-energy translational and rotational velocity trajectory planning and control system is presented on a straight-line path for three-wheeled omnidirectional mobile robots (TOMRs). We suggest an efficient online trajectory planning algorithm, which minimizes a practical cost function as the energy that is drawn from batteries to motors, which is based on an accurate TOMR dynamic model that includes both the Coriolis force and the actuator motor dynamics. Using Pontryagin's minimum principle, we find the minimum-energy rotational velocity trajectory in analytic form. Then, the minimum-energy translational velocity trajectory is found using a novel algorithm that has a time complexity of O(n), which is based on a linearity condition on the state transition of TOMRs. Moreover, a trajectory control system is implemented using the resolved-acceleration control to validate the actual performance. Simulation and experiment results show that these minimum-energy trajectories can save energy up to 4.76% compared with the energy-efficient trapezoidal velocity profile and up to 5.29% compared with the loss-minimization control.

Online Minimum-Energy Trajectory Planning and Control on a Straight-Line Path for Three-Wheeled Omnidirectional Mobile Robots

This paper proposes a feedback control scheme for an omnidirectional holonomic autonomous platform, which is equipped with three lateral orthogonal-wheel assemblies. Firstly, the dynamic properties of the platform are studied, and a dynamic model suitable for the application of control is derived. The control scheme constructed is of the resolved-acceleration type, with PI and PD feedback. The control scheme was experimentally applied to an actual mobile robotic platform. The results obtained show that full omnidirectionality can be achieved with decoupled rotational and translational motions. Omnidirectionality is one of the principal requirements for mobile robots designed for health-care and other general-hospital services.

Feedback Control of an Omnidirectional Autonomous Platform for Mobile Service Robots

In this paper, we describe a holonomic omnidirectional mobile robot with three orthogonal-wheel assemblies and its high accurate tracking control system. We first analyze three types in the realization of mechanical structure. We then develop an omnidirectional mobile robot using the lateral wheel assembly to obtain the much simpler control system. Several test results in the feedforward control system indicated that the mobile robot had a desirable full mobility and smooth motion. In order to realize a dynamic control system based on the model information, the dynamic model and its resolved acceleration control system are described. The effectiveness of the control system is demonstrated by a set of practical experiments.

Autonomous Control for an Omnidirectional Mobile Robot with the Orthogonal-Wheel Assembly

Recently, an industrial mobile robot has been required to have some abilities that it can freely travels within a confused factory and achieve an accurate positioning in a work station. For this purpose, an active investigation is now focused on the study of omnidirectional mobile robots, instead of a conventional mobile robot with two independent driving wheels, or with the front-wheel handling and rear-wheel driving. The omnidirectional mobile robot has been studied by using a variety of mechanisms. In particular, a holonomic vehicle has a full omnidirectionality with simultaneous and independently controlled rotational and translational motion capabilities. Several omnidirectional platforms have been known to be realized by driving wheel with steering (or offset driving wheel) [1], [2], [3], universal wheels [4], [5], spherical tires [6], or crawler mechanisms [7], [8].

Yamato Shiraishi

Papers

Feedback Control of an Omnidirectional Autonomous Platform for Mobile Service Robots

Autonomous Control for an Omnidirectional Mobile Robot with the Orthogonal-Wheel Assembly

Autonomous Control for an Omnidirectional Mobile Robot with Feedback Control System