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The cameras, projector and rotation stage are mounted rigidly with respect to each other, which is important for high quality results. See figure \ref{fig:hardware0} for an image of the inside of the main scanner assembly. A darkening curtain can be lowered, to prevent ambient light from interfering with the measurement procedure.
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The cameras, projector and rotation stage are mounted rigidly with respect to each other, which is important for high quality results. See figure \ref{fig:hardware0} for an image of the inside of the main scanner assembly. A darkening curtain can be lowered, to prevent ambient light from interfering with the measurement procedure.
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\begin{figure}[h]
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\begin{figure}[h]
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\centering
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\centering
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\includegraphics[width=.9\textwidth]{hardware0.jpg}
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\includegraphics[width=.9\textwidth]{hardware0.jpg}
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\caption{The scanner hardware. Two industrial cameras and one projector constitute the optical parts. An angel figurine acts as the scan object, and is placed on top of the circular rotation plate. This plate is screwed onto a microrotation stage. The calibration target is also seen on its holder.}
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\caption{The scanner hardware. Two industrial cameras and one projector constitute the optical parts. An angel figurine acts as the scan object, and is placed on top of the circular rotation plate. The calibration target is also seen on its holder.}
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\label{fig:hardware0}
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\label{fig:hardware0}
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\end{figure}
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\end{figure}
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The geometry of the scanner is illustrated on figure \ref{fig:hardwaredimensions}, which also indicates the minimum focus range of the cameras and projector.
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The geometry of the scanner is illustrated on figure \ref{fig:hardwaredimensions}, which also indicates the minimum focus range of the cameras and projector.
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\begin{figure}[h]
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\begin{figure}[h]
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\subsection{Cameras}
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\subsection{Cameras}
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These are high resolution 9MPx industrial CCD colour cameras. While colour information is usually not necessary in structured light, it enables us to full colour texture the scanned object. In the program code, a white balance is used for the camera, which was chosen ad-hoc to approximately match the colour profile of the projector. To capture real true colours, a colour calibration would have to be done.
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These are high resolution 9MPx industrial CCD colour cameras. While colour information is usually not necessary in structured light, it enables us to full colour texture the scanned object. In the program code, a white balance is used for the camera, which was chosen ad-hoc to approximately match the colour profile of the projector. To capture real true colours, a colour calibration would have to be done.
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\subsection{Rotation stage}
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\subsection{Rotation stage}
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This is a so-called micro-rotation stage, commonly used in high precision photonic research and production. A larger diameter plate was attached. The rotation stage has a stepper motor which drives a worm-gear. This gives high precision and very high repeatability. Note that the rotation stage does not have an optical encoder. It is reset to 0 degrees at each program start in software. The motor controller can be configured for different levels of microstepping and motor current. Higher motor current provides more torque and less risk of missing steps. Load on the plate should not exceed 20 kg, and be centered around the rotation axis. Objects can be stabilised on the plate using e.g. modelling clay.
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This is a so-called micro-rotation stage, commonly used in high precision photonic research and production. A larger diameter circular breadboard is fixed onto the rotation stage. The rotation stage has a stepper motor which drives a worm-gear. This gives high precision and very high repeatability. Note that the rotation stage does not have an optical encoder. It is reset to 0 degrees at each program start in software. The motor controller can be configured for different levels of microstepping and motor current. Higher motor current provides more torque and less risk of missing steps. Load on the plate must not exceed 20 kg, and the load's centre of mass rotation axis. Objects can be stabilised on the plate using e.g. modelling clay.
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\subsection{Calibration target}
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\subsection{Calibration target}
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A calibration target is also part of the scanner. It was produced by printing a checkerboard in vector format, and gluing it onto a thick piece of float glass using spray adhesive. The target is asymmetrical, which is necessary to uniquely match chessboard corners in both cameras. The calibration target was designed to fill the scan objects space. If you need a smaller scan area, a smaller calibration target would be beneficial.
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A calibration target is also part of the scanner. It was produced by printing a checkerboard in vector format, and gluing it onto a thick piece of float glass using spray adhesive. The target is asymmetrical, which is necessary to uniquely match chessboard corners in both cameras. The calibration target was designed to fill the scan objects space. If you need a smaller scan area, a smaller calibration target would be beneficial.
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\section{Software components}
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\section{Software components}
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