Domino Tape Printer

Our position-correcting router relies on a field of high contrast dominoes - which are easy for the computer vision system to identify - in order to locate itself.	The printing accuracy of each domino directly influences the cutting accuracy of the tool. We print a non-repeating pattern, making each tape field uniquely identifiable.
Each spool has alternating locating features and spring fingers to keep the tape concentric and retained.	Both the encoder wheel and drive motor are mounted on eccentric pucks, allowing the gear clearances to be precisely adjusted.
This rotational adjustment range can be seen in the slotted mounting features.	The tape passes under a 0.5"-wide inkjet nozzle.
One of the first challenges we faced was smearing of the standard water-based inkjet ink. The top surface of masking tape has a waxy release coating to keep it from sticking to itself, but also prevented the ink from drying.	Switching to a solvent-based ink solved the problem. Additionally, we installed a fan to improve the drying time and increase print speed.
Finally, a clean roll of printed domino tape!	A small celebration!
Next, we focused on accuracy and print speed. One element of this was replacing the 3D printed encoder wheel with a precisely turned aluminum wheel.	Here you can see the drive gear being pressed into the back of the encoder wheel on the lathe, to help improve concentricity.
Moving the encoder wheel further from the printhead improved accuracy by increasing the wrap angle of the tape, and enabled us to increase speed by lengthening the drying distance.	Quality control was performed by laying 10 ft of tape on the floor of my attic, and measuring the average domino pitch over that distance.
Once the printing process was dialed in, the tape printer became a vital piece of infrastructure that for several years supported our prototyping and user testing activities.	With significant effort from the broader team, we eventually switched over to the industrial printing process we use today.