Sunday, January 05, 2025
FPath: The Pantograph
My first physical step down the Feynman Path is a pantograph.
“What”, you say, “something that stopped being hi-tech in the 1700’s is somehow relevant on a path to Nanotechnology”. Well, no and yes. No, the pantograph is not really an optimal solution – I think flexures such as are being developed for the RepRapMicron are the more promising avenue… and... Yes. I do think machinery at the micro and nano levels will resemble massively parallelized versions of older solutions - maybe not the 1700’s but certainly the 1800’s. I will have more to say on this complexity vs simplicity issue in future blog posts.
Back to the point. My primary interest at the moment is how errors might be removed as big devices build smaller devices. The pantograph is a simple thing built out of LEGO bricks and has a reduction ratio of slightly over 5:1. The goal is to create a really nice, visible circle using closed loop feedback to iron out the errors as extremely inaccurate large scale actuators move the tool head about. The tool head has a barrel and lead scavenged from a mechanical pencil mounted on it to record the path.
The image above shows the pantograph. The macro end is on the left (red arrow) and the toolhead is in the center at the micro end (green arrow).
Closed loop control was used to drive the macro and micro ends around a circular path. The image on the left shows a typical path taken by the toolhead when the control was applied to the macro end (it is also supposed to be a circle). This forms kind of a baseline case representing the inherent accuracy of the hardware. The image on the right shows the path taken when the control was applied to the micro end of the pantograph.
It is
fairly clear from the image on the right that the errors attributable to the pantograph
mechanism have been greatly reduced by applying closed loop control to the
toolhead. Please see the webpage (FPath_Ex006) and short (8 min) video for more a more complete discussion.
Interestingly, both Heinlein and Feynman proposed using pantographs to have large machines make smaller machines. One reason I decided to use a pantograph as my “first device” is to acknowledge their ideas – a kind of homage if you will.
Labels: Feynman Path, FPath, Nanotechnology, Pantograph, Stigmergic Path Following
Sunday, December 08, 2024
FPath: Graphical Stigmergy
One of the major problems with the Feynman Path approach is minimizing and correcting the unavoidable errors as large tools make smaller tools. One way forward is to simply accept that the machinery will be imprecise and use a closed loop feedback system to help eliminate those errors. Developing such a control system is the reason why most of the work on the FPath Project has so far been software.
In Experiment 004 the Walnut software was used to demonstrate a path following and error correction behavior using real time object recognition. A rather crude XY stage was used to move a 5mm red circle along a green path. The green path is entirely virtual and is overlaid on the video stream by software.
The video documentation for Experiment 004 can be found at the link: https://youtu.be/bCb2k8tKX6k
If you watch the video you will see that cheap DC motors glued to LEGO bricks are used to move the tool head. Why do this? Surely something of higher quality would be better? Well, yes and no. Yes, the quality of the movement could be improved and it certainly would not be hard to find better alternatives to the gear motors currently in use. But no, I actually want the poor quality movement. The goal here is not to have accuracy handed to me on a plate but rather to get experience taking inaccurate tools and making the resulting output accurate. This is a simulation of what needs to happen when larger machines make smaller machines and there is no realistic way to improve the accuracy of the parent. Errors must be corrected and it is much easier to get some practice at this while still at the macro scale.
Stigmergy is the use of the environment to coordinate actions. If you watch the video you will get a sense of how Graphical Stigmergy could be a useful part of an error correction system.
Labels: Feynman Path, FPath, Graphical Stigmergy, Nanotechnology, Stigmergic Path Following
