Add end-effector cycle

content/case_experiment_end-effector.tex

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+With the preparation phase completed, the development cycle is next.
+This consists of three steps: Feature selection, Rapid Development and Variable Approach.
+The current section explains the first development cycle during the design.
+The end-effector is the feature that is selected in the first cycle.
+The implementation of the end-effector was not successful, as the design was too complex.
+Fortunately, this failure did give valuable insight on the design method.
+
+    \subsection{Feature Selection}
+        \begin{table}[]
+            \caption{Overview of the different features and their dependencies, number of tests that can be completed and the risk/time factor.
+            The risk/time factor is calculate as risk divided by time.}
+            \label{tab:firstfeatureselection}
+            \begin{tabular}{|l|l|l|l|l|l|}
+                \hline
+                Feature      & Dependees   & Tests  & Risk   & Time    & Risk/Time  \\ \hline
+                SCARA        & -           & 3      & 40\%   & 10 days & 4          \\ \hline
+                End-effector & SCARA       & 2      & 60\%   & 8 days  & 7.5        \\ \hline
+                Carriage     & -           & 2      & 30\%   & 10 days & 3          \\ \hline
+            \end{tabular}
+        \end{table}
+        The feature is selected according to the feature selection step, explained in \autoref{sec:feature_selection}.
+        For each component in the system the dependees, tests and risk/time factor is determined.
+        These values are combined into \autoref{tab:firstfeatureselection}.
+
+   %%%%%Euhm, ja dat staat dus niet in het initial design.
+        The SCARA is dependent on the end-effector, as was explained in the initial design.
+        However, for the carriage no dependency was defined even though it has to lift the other two components.
+        This is mainly because the behavior of the SCARA changes depending on the end-effector, resulting in a possible design change.
+        For the carriage it only changes the mass that has to be lifted.
+        Upgrading the motor torque is a minor parametric change and the dependency is therefore insignificant.
+
+        The testing number is directly the number of tests that can be completed by implementing that single component.
+        For the risk and time it was a engineering judgement and no specific protocol to determine the values.
+        The estimated risk is high for the end-effector due to the collision dynamics of the operation.
+        It has to grab something and that is difficult to model. Furthermore, it was not known if that design would work.
+        The SCARA has the most moving parts, but no difficult dynamics and has therefore an estimated risk of medium.
+        For the carriage the there was no real risks and got therefore a low risk indication.
+        
+        The SCARA would be implemented first based on number of tests, but is dependent on the end-effector.
+        Beginning with the end-effector is an obvious choices. 
+        It unlocks the SCARA and has the highest risk/time factor.
+
+        \subsubsection{Evaluation}
+            This first step of the detail design phase did go well.
+            A more refined method for this step could be very useful.
+            But the risk and time assessment will probably always be a engineering judgement from the developer.
+            Within a design team a form of planning poker\footnote{\url{https://en.wikipedia.org/wiki/Planning_poker}{Wikipedia entry: Planning Poker}} could be a good option.
+
+    \subsection{End-effector model}
+        The end-effector will operate as an interface between the SCARA and the different tools.
+        For that it has to be able to grab and release the tools.
+        The initial design is shown in \autoref{fig:gripper}. 
+        With only some experience in modelling with collisions the decision was made to try to make some collisions in the 20-sim 3D mechanics editor.
+        Unfortunately, collisions in a 20-sim model are difficult.
+        There is little tooling available and there are no debugging options if the model does not behave as expected.
+        The marker kept falling trough the gripper or flew away.
+        With the small amount of progress made in two days the implementation was not promising. 
+        A crash in the software caused the model to corrupt, where the complete configuration of the shapes and their collisions was lost.
+        Therefore it was decided that end-effector would be removed from the design.
+
+        With the end-effector removed, the SCARA will get a direct connection with the marker.
+        The lifting of the marker will be included in the SCARA as well.
+        Furthermore, this means that the wiping will no be possible via the SCARA.
+
+        \subsubsection{Evaluation}
+            The lost progress of the model is unfortunate, but the implementation did not go expected anyway.
+            It was probably for the best as it forced an evaluation of the design and avoided a tunnel vision while trying to get it to work.
+            However, it did show the value of the risk/time analysis.
+            This early failure resulted in changes for other components.
+            But as none of the components were implemented yet, no work was lost.
+