% -------------------------------------------------------------
% Contexto e motivação
% -------------------------------------------------------------
\section{Context and Motivation}\label{sec:context}
Postural balance is a concern that applies both to humans and bipedal robots. For humans, this issue is focused on detecting some pathologies, evaluating individual balance capability, and gather data on how equilibrium is maintained. On the other hand, the robot's postural study aims to evaluate the machine's control and help tune it.

%ORDENAR MELHOR ISTO, RETIRAR A REF PARA A SECÇAO DO PHUA!!!!!!

University of Aveiro Humanoid Project (PHUA) began in 2003/2004, as a result of a partnership between the Mechanical Engineering Department (DEM) and Electronics, Telecommunications and Informatics Department (DETI), of the University of Aveiro, with the purpose of creating a humanoid platform to study control, perception and behaviour. Its main goal is the development and application of hardware and software components in a functional low-budget platform, to carry out research in balance and locomotion tasks. The robot's current physical appearance is shown in Figure \ref{figure:phuaviews}.

	  \begin{figure}[!hb]
	  \centering
	  \includegraphics{Imagens/phua_views.png}
	  \caption{Front and side views of the PHUA platform's full body \cite{Serra}.}
	  \label{figure:phuaviews}
	  \end{figure}


The high degree of complexity associated with PHUA places some restrictions on the definition of accurate models to the study of motion patterns. Some work has been done on trying to take advantage of the concept of robot learning from demonstration, where a human user teleoperates the robot in different motion and balance tasks using a haptic joystick.  The data collected during the tests can be used in learning algorithms, so the robot will be able to move, balance and walk on its own \cite{Barros2014}.

Currently the humanoid project faces the problem of maintaining balance under perturbations. This means that the balance algorithms need to be studied better. To do this the induced perturbations have to be repeatable.%, to make sure if the humanoid responses are random or produced by its balance algorithms. 

Also, there is the possibility of extending this technique to humans (to study pathologies, assess the recovery of a patient, etc.).


% The  high  degree  of  complexity  associated  with  the  humanoid  robotic  platforms
% places  some  restrictions  on  the  definition  of  accurate  models  to  the  study  of  mo-
% tion patterns.  Thus, in the context of the University of Aveiro Humanoid Project -
% PHUA, some work has been done on trying to take advantage of the new concept of
% robot learning from demonstration, where a human user teleoperates the robot in
% diferent motion and balance tasks using a haptic joystick.  The data collected dur-
% ing the tests can be used in learning algorithms, so the robot will be able to move,
% balance and walk on its own. 


%Given the need to test PHUA's (\ref{sec:phua}) equilibrium, the idea of creating a balance disruption system came up, and considering that it is a humanoid robot, quickly, another idea followed, which was building a similar system to use on humans.
%Also, PHUA's control is based on a learning procedure, where information from human balance and gait cycles is gathered and then applied on the robot. This balance disruption system shall have contributions to the progress of the humanoid project, since it will collect information on how to maintain balance after a disturbance.

% -------------------------------------------------------------
% Decrição do problema
% -------------------------------------------------------------
\section{Problem Description and Solution Overview}\label{sec:probdesc}
For both robot and human, the chosen method to study postural equilibrium is done by applying a controlled and repeatable balance disrupting stimulus and measure responses, such as ground reaction forces, accelerations, body movements and energy expended. All this data will be analysed to obtain a model of the behaviour or set of reactions that counteracted the disturbance.

Measuring all these quantities can be achieved with a motion capturing system, a force plate, inertial systems and electromyography. For robots, this last technique can be partially replicated by measuring servo current consumption, for example.

For the success of this approach, the subject responses have to be precisely measured, and the stimuli must be well known, controlled and repeatable. Taking this in consideration, the first system to test the PHUA's balance will be a prototype of the human scaled one, which needs to be a servo-controlled system that can be applied in a biometric and motion capturing environment. Therefore, it must have a low visual influence, assure the subject safety, allow calibrations and adjustments as automatically as possible. 


So, the system to test PHUA's robot has to be designed taking all this in consideration.
Advancing to a possible solution, the type of stimulus to be used in the tests, can be traction forces (without excluding other possibilities) applied to the subject's body. Figure \ref{figure:1stsolution} visually describes this concept; the ropes would pull the subject in the posterior, anterior, right and left directions.

	\begin{figure}[!hb]
	\centering
	\includegraphics{Imagens/system_idea.png}
	\caption{Possible solution for the balance disruption system}
	\label{figure:1stsolution}
	\end{figure}

Servo motors would provide the tension needed, and backed up by force sensors, integrated on the ropes, to assure the stimulus data is stored and is within the desired range. On a final phase of the project, all other data will be gathered with the sensing infrastructure available in the motion capturing lab at ESSUA and by PHUA's own sensors. %The servo system should have an initial phase where it would calibrate, establishing a starting equilibrium state, and the tension on the ropes would be adjusted to a desired value.

As for the stimulus itself, one or two servos would pull, and the others would provide as much rope needed to maintain a certain tension, so that the subject doesn't become at risk of falling. Making the system like this, leaves room to use other types of stimuli that can be used alongside with this one, to interfere with the visual and vestibular systems.



% -------------------------------------------------------------
% Objectivos
% -------------------------------------------------------------
\section{Objectives}\label{sec:objectives}
The main objectives of this dissertation are the following:

%Development of a combined stimuli application model to generate controlled balance disruption. 

%Development of an integrated electromechanical model to apply stimuli to PHUA, using suitable components.

%Design of the mechanical, electrical and control components of the human scaled system.
\begin{itemize}
\item Conceive a mechanical set-up to test the concept.
\item Conceive and test stimuli patterns to the mechanical system in order to assess the reliability of the concept.
\end{itemize}



% -------------------------------------------------------------
% Guia da tese
% -------------------------------------------------------------
\section{Thesis Guide}\label{sec:guide}
The stages of this work are presented in the following chapters, organized as follows:

\begin{itemize}
\item Chapter \ref{chap:intro} gave the context and motivation for the current work as well as description of the problem, an overview of the solution and explained the objectives.
\item Chapter \ref{chap:back} compiles relevant information for this project. It briefly presents human balance, balance testing systems and force control with servo motors.
\item Chapter \ref{chap:exp} details the hardware and software used in this work. More specifically it presents the characteristics of: PHUA; the servos and the interface to communicate with them; the sensors and their acquisition unit; the software platform.
\item Chapter \ref{chap:pendu} documents experiments done with an inverted pendulum. It presents strategies to achieve a state of balance.
\item Chapter \ref{chap:stimu} documents experiments done with the inverted pendulum. More specifically, some stimuli are applied to the pendulum and the results are presented and discussed.
\item Chapter \ref{chap:conc} discusses the main conclusions of this dissertation work, and presents some proposals for future works.
\end{itemize}


