Development of a robotic system for automating synthetic chemistry workflows using visual feedback
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Date
2026-10-06
Authors
Καρατράντος, Βασίλειος
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Abstract
This thesis develops a robotic system for automating liquid-handling procedures in a chemistry laboratory, using a seven-degree-of-freedom manipulator that locates the objects it handles by fiducial markers, observed by a camera before each operation, rather than replaying coordinates fixed in advance.
The task imposes a requirement that governs the whole design: the arm carries an open test tube containing liquid, and the tube must remain vertical throughout its motion and not merely at the endpoints. In motion-planning terms this is a path constraint on the orientation of the end-effector, and it confines the admissible configurations to a surface of measure zero within the space a sampling-based planner explores. General-purpose planners address such constraints by rejecting samples or by projecting them numerically, and both remedies are expensive and satisfy the constraint only approximately.
The contribution of this work is to remove the constraint from the search rather than to enforce it during the search. The manipulator has a spherical-shoulder, revolute-elbow, spherical-wrist structure, which is established here from its kinematic model, and which admits a closed-form inverse solution. Exploiting that structure, an explicit analytic chart of the constraint surface is constructed, so that the planner searches a five-dimensional parameter domain each point of which maps in closed form to a complete seven-joint configuration. Within the nominal kinematic model of the arm, no configuration violating the constraint can be produced, because none exists in the space being searched.
Three planning architectures are built and compared: constrained search in the full joint space, a conservative four-dimensional reduction reported as a measured negative result, and the analytic chart. On the physical arm the chart planned each of the transits it handled in 7.7 - 80.5 ms with a maximum planned tool tilt of 0.00035°, against 457 to 7055 ms and tilts of up to 33.0° for the constrained baseline on the transits the chart declined. On a common benchmark of the same transits, repeated ten times per method, the chart planned about twenty times faster than the baseline. In a proof-of-concept evaluation, fourteen of sixteen complete transfers succeeded.
The system is assembled from a low-cost educational manipulator, a commodity webcam, printed fixtures and open-source software, and is operated through a graphical interface requiring no knowledge of the algorithms beneath it.
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Keywords
Robotic manipulators, Kinematic redundancy, Constrained motion planning, Constraint manifolds, Closed-form inverse kinematics, S-R-S structure, ArUco markers, ROS 2, Laboratory automation