Robot's walking

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Chapter 5

Robot's walking
5.1 Introduction
The biped walking process or biped locomotion area has been studied for a
long time, but it is only in the past years, thanks to the fast development of
computers, that real robots started to walk on two legs. Since then the problem
has been tackled from dierent directions.
First, there were robots that used static walking. The control criteria was
to maintain the projection of the center of gravity (COG) on the ground, inside
of the foot support area.
This approach was abandoned because only slow walking speeds could be
achieved, and only on at surfaces.
For the dynamic walking robots the center of gravity (or center of mass) can
be outside of the support area, but the zero momentum point (ZMP), cannot [33].
The ZMP criteria has been broadly used to generate biped control algorithms
[34], [35].
In this thesis, the walking problem is divided and focus on two themes: the

balance control and the walking sequence control.
In balance control, a feedback-force system at each robot's foot was implemented to calculate the ZMP and then feed it in to the incremental fuzzy PD
controller to decrease the ZMP error [14]. The controller's goal is to adjust the
lateral robot's positions to maintain the ZMP point always inside of the support
The walking sequence control of a biped robot can be determined by con-



Single support phase
Stable position

Double support phase
Stable position


Unstable position

Figure 5.1: Static walking.
trolling the hip and foot trajectories [15]. To achieve stable dynamic walking,
the change between simple supports walking phase and double supports walking

phase should be smooth. In this thesis cubic polynomials algorithms are used to
control the sagittal motion and guaranties a smooth change between the walking
phases [6].
The robot's stability at dynamic walking was achieved applying the ZMP
criteria in the incremental fuzzy PD controller to guaranties the balance control
at walking [14] and the cubic polynomials algorithms to control the walking
sequence control.
In the next sections, the static and dynamic walking are presented, the ZMP
concept is widely explained, then the balance control and the walking sequence
control are explained.

5.2 Static walk
Static walking assumes that the robot is statically stable. This mean that, at
any time, if all motion is stooped the robot will stay indenitely in a stable
position. It is necessary that the pr...
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