mar/content/case_experiment_recap.tex

%&tex
    \subsection{Recap}
            During the problem definition and the specifications step it was difficult to stay within the "what" has to be solved and not go into the "how" it has to be solved.
            Furthermore, the test definitions of the last step conclude the preliminary design phase.
            This preliminary design shows a clear notion of a hasty execution from a design standpoint.
            The preliminary design was performed over a period of 5 weeks, by one developer with little experience in design documentation.
            This makes notion of hasty not surprising for this unproven design method.
            That does not mean that this preliminary design is a waste of time.
            From the evaluation moments during the preliminary phase there are a couple of interesting points.
            \begin{itemize}
                \item The lack of a design team with experienced engineers would drastically improve the execution of this design phase.
                    Such a team is also able to find the smaller problems of such a design phase, which are currently completely overlooked.
                \item It is not possible to view each step in the design process as singular.
                    Each step creates more insight and information about the final design.
                    Making a very strong separation between the steps forces the developer to make decisions on to little information.
                \item The term features has to be split in to functions and components for a hardware design.
                    The actual implementation are the components such that they can perform the function.
            \end{itemize}

            Another point was noticed while evaluation the complete preliminary design phase.
            The lack of a team makes it easy to forget documenting intuitive design decisions.
            Although the design method is followed as closely as possible, it often occurs that a decision is made outside of the working environment.
            This was noticed during the writing of this chapter that some design decisions were completely missing.
            However, during the next phase, these decisions do play a crucial role.
            Therefore, this section will give a short recap of the planned design.

            \subsubsection{Complete system}
            From the initial design the abstract shape of the design is clear.
            This is still in line with \autoref{fig:general_design}.
            The SCARA is small and can therefore move the arm quick with a fine precision.
            At the end of the SCARA there is a end-effector that can grab, hold, end release tool.
            It holds a marker while writing and with help of the SCARA it can release the marker.
            Then it can grab a cleaning tool to erase whiteboard.
            To compensate for the small reach of the SCARA, the SCARA will be mounted to a carriage.
            This carriage is suspended from cables and can move along the whiteboard.
            The cables give the system a enormous range and velocity.
            However, it is not very good in acceleration as cables cannot push.
            This makes it suitable for the large and course movements along the board, which complements the movement characteristics of the SCARA.



            \subsubsection{SCARA}
            The central component of the system is the SCARA.
            There are a couple of design options for the SCARA.
            As the dynamic complexity is a important part of this design, there will be two arms.
            There are some different options for the configuration of the arms and their actuation.
            \autoref{fig:configurations} shows four of the possible configurations that are considered during the design phase.
            There are still options about where to place the motors and how to connect the joints.
            \rrot{Figure needs some graphic improvement}
            %\begin{figure}
            %    \centering
            %    \includegraphics[width=\linewidth]{graphics/IMG_20201001_134140.jpg}
            %    \caption{Four different SCARA configurations}
            %    \label{fig:configurations}
            %\end{figure}

            \subsubsection{End-effector}
            The end-effector is the connection between the SCARA and the tool.
            It has two main functions: lifting the tool from the board and switching the tool.
            The tool switching functionality is performed by the SCARA as well, by moving the end-effector to the right position.
            However, the role of the SCARA is strongly dependent\footnote{ Note, that this dependency exists but not represented in \autoref{fig:robmosys} due to the limitation of the current method.} on how the end-effector is implemented.
            For the grabbing function there is a configuration that uses a spring-loaded clamp.
            Where one side of the clamp is longer so it can be opened by moving the SCARA.
            This operation is shown in \autoref{fig:gripper}
            %\begin{figure*}
            %    \centering
            %    \includegraphics[width=\linewidth]{graphics/IMG_20201001_144018.jpg}
            %    \caption{Operation principle of a spring-loaded tool clamp showed from left to right. The green circle represents the tool and the red arm a tool holder. The solid ground is what pushed the upper arm open so the marker can be placed in the tool holder.}
            %    \label{fig:gripper}
            %\end{figure*}

            Another dynamically simpler option is to open the clamp with a motor.
            The motor adds weight to the end-effector which might require the SCARA to operate slower or to be build stronger.
            This component is probably the most difficult one because it requires clamping of the tools.
            Modeling this behavior is difficult as it will involve contact dynamics.

            \subsubsection{Cable driven Carriage}
            The end-effector and the SCARA are moved all together on a carriage.
            The carriage will be suspended from two or four cables.
            A configuration with two cables is the simplest.
            However, the tension in this system is generated by the gravitational pull.
            This introduces limitations in the acceleration of the system.
            If the carriage moves upwards and the cable pulleys stop.
            The carriage is only decelerated by the force of gravity.
            Moving over its set point, followed by crashing down in to the cables.

            However, making the system with four motorized pulleys makes the system over constrained.
            This will solve the acceleration problem. But it will create a difficult positioning system.
            As all the wires have to be tensioned but not distort the movement by restricting the other motors.

            \subsubsection{Electronics}
                Although this mainly is a hardware design, there is going to be some control-software.
                For this the likely option is a STM nucleo board with RIOT-OS as a embedded OS.
                This choice is mainly because of previous experience and local knowledge of the operating system.