I created a prototype 3D printer filament alarm that worked, but the process also brought some new problems and issues to the surface that I hadn’t foreseen when I first started. Today I’m going to dive further into the prototyping process to gain some insight on designing for a well-specified problem. What I came up with is an easy to build pendant that passively hangs from the filament and alerts you if anything about that changes.
I began with a need to know when my 3D printer was out of filament, so that I could drop whatever I was doing and insert a new spool of filament right up against the end of the previous spool. By doing this within four minutes of the filament running out, printing very large jobs could continue uninterrupted. The device I designed was called Mister Screamer.
The Basic Concept
The idea is that if a 3D printer is attended (but not under constant supervision) and the operator is prepared to swap filament rolls when needed, then there is no need for the printer to perform any “smart” duties such as pausing the print. As long as there is a means of triggering an alarm when filament has run out, the operator can do everything needed to keep the machine printing uninterrupted, and the printer itself doesn’t even need to know.
The previous prototype physically sensed filament with a roller switch that triggered a buzzer when filament ran out. It had a successful trial run, but revealed some new problems:
- When pulling filament through the device by hand there was little to no resistance felt, but once it was riding a roll of filament in the printer it created much more binding and friction than expected. Printing was successful but the printer’s extruder had to work much harder than usual. I had hoped the device would put a negligible strain on the feed system and filament. This was not the case.
- When filament ran out, the device fell some distance to the tabletop. This was expected. But the impact almost knocked the batteries completely loose from the friction-fit battery holder, which was not expected. Had the batteries popped completely out, the device would not have done its primary job. The device needed to be drop-resistant, but the prototype design did not reflect this.
Even though the previous prototype did the job it was supposed to do, it was clear there were problems and a design update was needed.
Design Goals Summary
The fundamental requirements for Mister Screamer haven’t changed much. The device’s duties are:
- If filament is present, nothing happens.
- If filament runs out, scream your fool head off to alert a nearby operator.
Other elements of the design worked out well enough to keep, and remain mostly unchanged:
- Enclosure can be 3D printed
- Self-contained (no external power or signals)
- Requires no modifications to the 3D printer to be monitored
- Electrically simple, and using a minimum of easy to source parts
- Long battery life, low power usage
- Easy to turn off when responding to an alarm
Lessons from building and testing the first prototype were used to add the following design goals:
- Must not interfere with the printer’s normal operation. Ideally, the printer should not even notice it.
- Device must be rugged and drop-resistant.
- Ability to easily add the device to the filament of a print already in progress.
The New Prototype
The new prototype keeps the same basic function, but with an entirely different approach. The device is now sensitive to orientation, and senses the actual filament only indirectly. It is designed to hang by a ball-link chain like a pendant.
While the device hangs down it is silent. If it falls, the alarm sounds until it is picked back up. Therefore in operation…
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