Closed loop control of slippage during filament transport in molten material extrusion

In the quest to achieve functional 3D printed parts with open source machines and tools it is required to study all the error sources. Flow control is a major contributor to accuracy of parts manufactured additively with material extrusion and a precise filament feed rate is therefore essential. Filament slippage is measured in this work. The speed difference between filament feed gear speed and filament speed is measured with a cost effective, automated setup, using a low cost USB microscope video camera and image processing. The filament width is also measured simultaneously, allowing for real time volumetric flow rate estimation. Extrusion temperature and feed rate are found to influence the amount of slippage. Significantly, the amount of slippage varies dynamically and therefore cannot be fully corrected for statically. Proof of concept closed loop control of the extruder is also implemented and reduces the amount of slippage considerably.