@[osf](zptyn) ### Open Source 3-D Filament Diameter Sensor for Recycling, Winding and Additive Manufacturing Machines **Highlights** - Developed a portable optical computer vision-based diameter measurement system. - The module can be integrated into a control system of a plastic waste recycling machine. - Multi-axis measurements with ovality detection and texture analysis assure quality. - Measurement logging allows tracking the quality of the filament along its length. **Abstract** 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. --- **Wiring diagram** @[osf](tuws9) --- **Image acquisition scheme** @[osf](zqg8j) a) image acquisition based on the pinhole camera model; b) filament projection in the absence of mirrors; c) filament projection with two mirrors installed at 45-degree angles --- **Filament segmentation and diameter measurement procedure** @[osf](qkry6) a) single camera frame; b) segmented filament; c) rectified regions reveal filament thickness and its surface structure based on light intensity. The red lines represent the detected filament centerlines, while the green ones represent their straightened counterparts, making it easier to concatenate adjacent texture sections together. --- **Edge segmentation process** @[osf](k5ut8) a) grayscale input images with the selected single-pixel slices (white vertical bars); b) filament edges detected for the single-pixel image slices demonstrated for red, gray and transparent filament. --- **Measurement logging** @[osf](peytb) a) diameter and ovality measurements during the winding process; b) diameter distributions for the main image and upper and lower mirror reflections. Dashed and dotted lines represent the manufacturer's declared diameter and ovality tolerance limits, respectively.