  To overcome the challenge of upcycling plastic waste into 3-D printing
filament in the distributed recycling and additive manufacturing systems, this
study designs, builds, tests and validates an open source 3-D filament diameter
sensor for recycling and winding machines. The modular system for multi-axis
optical control of the diameter of the recycled 3-D-printer filament makes it
possible to analyze the surface structure of the processed filament, save the
history of measurements along the entire length of the spool, as well as mark
defective areas. The sensor is developed as an independent module and
integrated into a recyclebot. The diameter sensor was tested on different kinds
of polymers (ABS, PLA) different sources of plastic (recycled 3-D prints and
virgin plastic waste) and different colors including clear plastic. The results
of the diameter measurements using the camera were compared with the manual
measurements, and the measurements obtained with a one-dimensional digital
light caliper. The results found that the developed open source filament
sensing method allows users to obtain significantly more information in
comparison with basic one-dimensional light sensors and using the received data
not only for more accurate diameter measurements, but also for a detailed
analysis of the recycled filament surface. The developed method ensures greater
availability of plastics recycling technologies for the manufacturing community
and stimulates the growth of composite materials creation. The presented system
can greatly enhance the user possibilities and serve as a starting point for a
complete recycling control system that will regulate motor parameters to
achieve the desired filament diameter with acceptable deviations and even
control the extrusion rate on a printer to recover from filament
irregularities.
