Navegación De Robots

A Robocentric Motion Planner for Dynamic Environments
Using the Velocity Space
Eduardo Owen †‡

Luis Montano †

‡Escuela de Ingenier´a El´ ctrica y Electr´ nica
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Universidad del Valle
Calle 13 No. 100-00, Cali, Col
efowen@unizar.es

†Instituto de Investigaci´ n en Ingenier´a de Arag´ n
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Dep. Inform´ tica e Ingenier´a de Sistemas, Universidad de Zaragoza
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Mar´a deLuna 3, E-50018 Zaragoza, Spain
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montano@unizar.es

Abstract— This paper addresses a method to optimize the
robot motion planning in dynamic environments, avoiding the
moving and static obstacles while the robot drives towards
the goal. The method maps the dynamic environment into a
model in the velocity space, computing the times to potential
collision and potential escape and theassociated robot velocities.
The problem of finding a trajectory to the goal is stated as a
constrained nonlinear optimization problem. The initial seed
trajectory for the optimization is directly generated in the
velocity space using the model built. The method is applied
to robots which are subject to both kinematic constraints
(i.e. involving the configuration parameters of the robot and
theirderivatives), and dynamic constraints, (i.e. the constraints
imposed by the acceleration/deceleration capabilities). Some
experimental results are discussed.

map of all the collision-free velocities available. An initial
collision-free trajectory is computed on the model, which
is utilized as a seed in the optimization procedure to find
a trajectory which converges to the goal. Thisprocess is
resumed every sampling time.
This paper is organized as follows: in section II some
related works are presented. In section III the developed
approach is outlined. Section IV presents the method to map
the configuration space of a dynamic environment to the
velocity space. The robocentric motion planning algorithms
are addressed in V. The optimization of trajectories using the
velocityspace built is presented in section VI. Simulation
results are discussed in section VII and in section VIII some
conclusions are presented.

I. I NTRODUCTION

II. R ELATED W ORKS

This work addresses a method to plan robot motions in
dynamic environments. It concerns to find a trajectory from
start to goal that satisfies: i) avoids obstacles in the environment, ii) the trajectories arefeasible (kinematic and dynamic
constraints of the robot), and iii) minimizes a criterium (i.e.,
motion time). The collision avoidance problem in motion
planning has been extensively treated in the robotics literature
and recent methods based on reactive avoidance already consider some of these constraints. When the available velocity
information of the moving objects is taken into account, thenavigation system can compute more stable trajectories which
improve the motion performance regarding others classical
methods for motion planning. The information gathered by
the sensors of the robot which reflects the dynamism of the
environment it is necessary to plan optimal or near-optimal
trajectories.
This way we use a technique to plan robot motions which
transform the problem fromthe workspace or configuration
space to the velocity space in order to make decisions about
the ”best” strategy of motion directly in this space. The
method maps the positions of the obstacles and their known
or estimated trajectories into the velocity space of the robot
taking into account its kinematic and dynamic constraints.
It provides information about further collisions, providing aThe classical reactive methods such as [21], [3], [11], [20]
are sufficient to keep the robot safe, but they are very sensitive
to local minima. The common approach is to incrementally
build a occupance grid, which assumes static obstacles and is
updated from sensor data. These approaches usually exploit
their reactivity to deal with moving obstacles. But they do
not use the kinematic...