\chapter{Conclusions and Future Work}\label{chapter:conclusions}
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The conclusions of this work are detailed the next Section, evaluating the success of the proposed objectives. The Future Work Section gives proposals for the continuation of this work and future of this project.
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\section{Conclusions}\label{sec:conclusions}

The first objective of this work was to implement the ROS platform in the PHUA. This has been done successfully; the modular capabilities of this platform are very useful for this project, where treating each problem separately has shown immense potential. The message communication system of ROS works well with the problems presented here. It allowed for a easy data transmission mechanism and an easy visualization. The usage of the \textit{rosbag} utility needs to be rethought; the loss of messages is problematic for future work of robot teaching from demonstration algorithms.

The data acquisition unit for the load cells was successfully developed and tested. The retrieval of the load cells signal is solid and stable and it gives the project a reliable source for environment sensing. There is still space for improvement now that this design was tested and proven to work, more is explained in Section \ref{subsec:future_hardware}.

Thanks to the modular software development and message communication, the link between the load cells information and the haptic force feedback was successful. Although the concept is proven, it still needs improvement in the force generation functions for a better sense of feel by the operator. A multiphase polynomial formulation may be worth to explore \citep{cruz_haptic_2012}. The formulation presented in this work (and future ones) should be tested with multiple users after which they give testimony in order to pinpoint the optimal solution.

The control of the PHUA robot's legs by the PHANTOM haptic device was successful; the control in position is capable of correcting the position of the robot. A speed based control is the next step for this project as is referred in Subsection \ref{subsec:future_control}.

Even though the used kinematics worked well in the demonstrations, there is a lot space for improvement in this part of the project. The continuation of the work here developed needs a full mathematical formulation for the control of both legs simultaneously with torso integration, direct, inverse and differential kinematics. This will allow for three dimensional control in both position and velocity.

The demonstrations were successful in different levels. The first one proved the concept of tele-operation of the robot by the haptic device where servomotors responded with little delay to the implemented kinematics. The load cells showed a quick and stable response to the movements of the robot giving the calculated COP a great accuracy. In the second experiment, even with the transmission slip, it was proven that the user can feel enough force on the haptic device to keep the robot in a stable position. The fact that only three load cells sense more than the pre-compression did not interfere with the behaviour of the COP; even then, for all the cells to be in contact with the floor and have a complete knowledge of the COP a proposal in given in Subsection \ref{subsec:future_hardware}. The force feedback's dead zone proved to be an asset to the tele-operation system as it prevented instability due to positive feedback and straining on the user's manipulation of the device. The last demonstration aimed to gather further knowledge for the preparation of the walking gait. Although more experiments with sophisticated kinematics are needed, it proves that the robot can perform the forward balancing motion that is needed for the gait.


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\section{Future work}\label{sec:future}


\subsection{Software}\label{subsec:future_software}

The software developed in this work can now be considered the base for further development in this project. With the ROS platform, the project can evolve each module separately with little or no repercussion to the rest of it. More software modules can be added depending on the needs of the project.

The path for growth in this project is the refinement of the haptic force generation and the robot control. The force generation can be further developed in terms of mathematical formulation to increase the feel of the robot's unbalance by the user. More on this subject in Section \ref{subsec:haptics}.

The robot control needs more refining. Due to the small force workspace, a velocity control instead of a position control may bring improvements. This might be difficult though because of the servomotors communication. These particular servomotors can only handle position or speed commands making this type of control complex.

\subsection{Haptics}\label{subsec:haptics}

The haptic interface has a lot to be developed in this project. It needs more improvement in terms of force generation and possibly more sources of information for a better feel for the user.

Different approaches should be taken to the force generation. In this work only two dimensional forces were created, a third direction may improve the user experience by creating a more intuitive interface. A possible use for the third force component is the effect the inertial forces at the end of the movements; the data for this effect can be accounted for by the total forces of each foot. In the generation itself, more complex mathematical formulations should be attempted, polynomial, exponential or sets of both can be experimented on different users for a more practical interface.

There is also space for more sensory information. The addition of other types of sensors, like inertial or tilt, can bring additional information and complexity to the force feedback generation. Each type of sensor needs a module to read/communicate with the sensor and then a new \textit{node} in the \textit{haptic\_force} module can be written to translate the new type of information into force feedback. Only after these steps can all the sensory data be merged into a single force generation routine.

\subsection{Command}\label{subsec:future_control}

The command of the servomotors present in the PHUA robot needs a refinement. A more comprehensive study of both the haptic device's and the robot's kinematics needs to be done. Another possible solution for the command issue is the use of two haptic devices, one for each leg. Although this can bring a lot of control problems, it represents the possibility to execute more complex movements, like one leg balancing or a human-like walking gait. When implemented, the torso's joints can work in function of the COP's deviation to help with the robot's balance.

To prevent saturation of the serial communication line for the servomotors, the usage of multiple serial lines where one line commands one member of the robot; this may require a rearrangement of the software control with a \textit{node} for each line/member and a central one to control them all. This will bring more the need for computer power for this project, possible solutions for this issue are addressed in the next Subsection.

\subsection{Hardware}\label{subsec:future_hardware}

The continuation of this work in terms of hardware passes through the reduction of size of the data acquisition unit for the load cells. A smaller unit capable of being installed in the robot's shin is the ideal solution. The ARDUINO Nano board is similar and smaller to the Fio and can easily be placed in the robot. The signal acquisition board can be adapted with smaller component packages (SOIC or QFP) to fit the Nano board footprint and pin layout.

One of the problems encountered during the experiments was the spiking of the belted transmissions teeth's due to the low contact ratio between the servomotor's pinion and the belt. This requires an intervention on the ankle's Inversion/Eversion and the hip's Abduction/Adduction that has a similar reduction; a stretcher for the belts or a change in the reduction may solve the problem.

A solution for the over usage of the CPU and RAM can pass through the application of the \textit{peer-to-peer} capabilities
of ROS; this allows for the ROS \textit{nodes} to be launched in different machines while keeping the ROS messages socket system working between them. This way a distributed system can be used form controlling the PHUA robot increasing the computational power.


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