Hi!
Had this idea for a while to combine the smooth delivery of Bowden with the agility of direct-drive.
Bowden fitting on the hot-end is mounted to small servo-motor (3mm +/- throw from 'neutral' position) so the spacing between nozzle and Bowden tube can be adjusted on the fly.
The Extruder doesn't pull the filament back for retraction, it just stops feeding.
The servo pushes the Bowden fitting farther from the nozzle, making the filament pull back from the nozzle.
Bowden tube and filament compression/drag/springiness are no longer part of the problem!
This results in much faster retraction, more precise pressure regulation.
Gone are the days of grinding filament during every retraction cycle!
As a bonus, monitoring servo drive-current can give a good estimate of force applied to the filament.
The servo uses feedback to maintain a command position relative to the nozzle.
As force against the Bowden fitting changes over time (normal printing, clogged nozzle, retraction), the power consumption will rise and fall.
One could 'read' power use activity and tell the printers health in near real-time.
Zero nozzle pressure = minimal current to hold servo position.
Slight 'negative' force on the filament could signal reaching a retraction goal.
Jammed nozzle = maximum force, plus or minus! Can't push, can't pull, stop please.
For some fun, modulate the servo to paint images on printed surfaces.
Rapid fluctuations in nozzle pressure would leave impressions on the surface, making flat surface lithophanes.
Robert is your parents sibling.
