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@ -63,6 +63,7 @@ Desktop\footnote{\url{https://signal.org/download/}}, Telegram
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Desktop\footnote{\url{https://desktop.telegram.org/}}).
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\subsection{Market analysis of available mechanical keyswitches}
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\label{sec:market_forces}
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To gather information about available actuation forces, we collected the product
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lines of keyswitches for all well known manufacturers, namely
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Cherry\footnote{\url{https://www.cherrymx.de/en/mx-original/mx-red.html}},
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@ -83,7 +84,7 @@ actuation force is 35 g ($\approx$ 0.34 \gls{N}) the most common one is 50 g
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\begin{figure}[ht]
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\centering
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\includegraphics[width=1.0\textwidth]{images/keyswitches_brands}
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\includegraphics[width=0.8\textwidth]{images/keyswitches_brands}
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\caption{Available actuation forces for keyswitches of major keyswitch manufacturers}
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\label{fig:keyswitches_brands}
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\end{figure}
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@ -105,5 +106,100 @@ subjects were all personal contacts. Subjects professions were distributed as
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follows: computer science students (3/6), physiotherapist (1/6), user experience
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consultant (1/6) and retail (1/6). All Participants were given instructions to
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exert maximum force for approximately one second onto the key mounted to the
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measuring device described in Section \ref{sec:force_meas_dev}. The order of
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positions in which the participants had to press the key was complete counterbalanced
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measuring device described in Section \ref{sec:force_meas_dev}. We also used a
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timer to announced when to press and when to stop. We provided a keyboard to
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every participant, which was used as a reference for the finger position before
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every measurement. To reduce order effects, we used a balanced latin square to
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specify the sequence of rows (top, home, bottom) in which the participants had
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to press the keys \cite{bradley_latin_square}. Additionally, because there were
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only six people available, we alternated the direction from which participants
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had to start in such a way, that every second subject started with the little
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finger instead of the index finger. An example of four different positions of
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the finger while performing the measurements for the keys \textit{Shift, L, I}
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and \textit{Z} can be observed in Figure \ref{fig:FM_example}.
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\begin{figure}[ht]
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\centering
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\includegraphics[width=1.0\textwidth]{images/FM_example}
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\caption{Prototype of the force measuring device used to gather data about the
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maximum applicable force to a key with different finger positions. The
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positions for certain keys are simulated by aligning the wrist pad (left
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picture) to the scale of the device. The four different positions for the
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keys \textit{Shift, L, I, Z} (right pictures) are color coded according to
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the keys on the scale}
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\label{fig:FM_example}
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\end{figure}
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The results of the measurements are given in Table \ref{tbl:finger_force}. The
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median of the means (15.47 N) of all measurements was used to calculate the
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actuation forces in gram for the keyswitches later incorporated in the layout
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for adjusted keyboard. We used Eq. (\ref{eq:N_to_g}) and
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Eq. (\ref{eg:actuation_forces}) to calculate the gram values for each measured
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keyswitch.
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\begin{equation}
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\label{eq:N_to_g}
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GFR = \frac{50 g}{M_{maf}} = \frac{50 g}{14.47 N} = 3.23 \frac{g}{N}
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\end{equation}
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\begin{equation}
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\label{eq:actuation_forces}
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AF_{key} = GFR * MAF_{key}
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\end{equation}
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With $M_{maf}$ the median of the means of applicable forces, $50 g$ the most
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commonly found actuation force on the market (Section \ref{sec:market_forces}),
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$GFR_{key}$ the gram to force ratio, $MAF_{key}$ the median of applicable force
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for a specific key and $AF_{key}$ the actuation force for that specific key in
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grams.
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An example where we calculated the theoretical actuation force for the \textit{P}
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key can be seen in Eq. (\ref{eq:force_example}).
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\begin{equation}
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\label{eq:force_example}
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AF_{P} = GFR * MAF_{P} = 3.23 \frac{g}{N} * 10.45 N \approx 33.75 g
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\end{equation}
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Because there are only certain spring
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% Custom spring stiffness
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% https://www.engineersedge.com/spring_comp_calc_k.htm
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\begin{table*}[]
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\centering
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\ra{1.3}
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\begin{tabularx}{13cm}{?l^l^l^l^l^l^l^l}
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\toprule
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\multicolumn{8}{c}{\textbf{Bottom Row}}\\
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\rowstyle{\itshape}
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\emph{Key} & ↑ & - & : & ; & M & N & B \\
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\midrule
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\emph{Mean Force (N)} & 11.23 & 10.84 & 14.22 & 15.34 & 16.38 & 15.6 & 14.36\\
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\emph{Actuation Force (g)} & 36.05 & 34.8 & 45.65 & 49.24 & 52.58 & 50.08 & 46.1\\
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\end{tabularx}
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\begin{tabularx}{13cm}{?l^l^l^l^l^l^l^X}
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\multicolumn{8}{c}{\textbf{Home Row}}\\
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\rowstyle{\itshape}
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\emph{Key} & Ä & Ö & L & K & J & H &\\
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\midrule
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\emph{Mean Force (N)} & 11.88 & 12.27 & 15.84 & 18.56 & 17.78 & 18.43 &\\
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\emph{Actuation Force (g)} & 38.13 & 39.39 & 50.85 & 59.58 & 57.07 & 59.16 &\\
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\end{tabularx}
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\begin{tabularx}{13cm}{?l^l^l^l^l^l^l^l}
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\multicolumn{8}{c}{\textbf{Top Row}}\\
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\rowstyle{\itshape}
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\emph{Key} & + & Ü & P & O & I & U & Z \\
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\midrule
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\emph{Mean Force (N)} & 10.8 & 10.7 & 10.45 & 14.34 & 17.95 & 17.0 & 16.8 \\
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\emph{Actuation Force (g)} & 34.67 & 34.35 & 33.54 & 46.03 & 57.62 & 54.57 & 53.93\\
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\bottomrule
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\end{tabularx}
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\caption{Maximum force measurements for all digits of the right hand in
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different positions. The mean force of six participants is shown in the
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first row of each table and the resulting actuation force for the
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corresponding keyswitch in the following row. The columns indicate the label
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of the scale on the measuring device which can be seen in Figure
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\ref{fig:FM_example}. \textit{↑} stands for the shift key.}
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\end{table*}
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phga
4 years ago
