Reliable Filament Runout Sensor

thingiverse

Human: [ Edit Feb 27 2018: See also the recent (and still more thorough) "Even More Reliable Filament Runout Sensor and Spool Holder" -- https://www.thingiverse.com/thing:2809260 ] Here is my design for a more reliable filament runout sensor, designed for mounting on and below a 2020 bar. I'm using it on a Folgertech FT-5, with the filament spool above it, but it should be usable with other printers with similar bars for mounting. **Background** I've been trying to install a reliable sensor for some time (tried like about six different designs including several variations of some of those!) but always seemed to run into problems. My issues might be from the type of printing I've been doing -- large objects printed with a wide nozzle so that filament gets used quickly (which is why there is urgent need for a sensor!) and the filament usually moves through the system quickly causing vibration and significant tension changes. Sensors that depend on filament directly pushing a microswitch closed, while seemingly simple, turned out to be a balancing act between having the switch tight enough against the filament that it causes a drag on the extruder and losing any kind of reliable signal from the sensor. The same problem occurs when trying to rely solely on optical sensors, which often get confused by the varying reflectivity of the filament. **Design Overview** This design uses an opto-interruptor to detect the presence or absence of a thin printed flag, which is attached to the end of the spool and can be easily seen through the gap in the interruptor. When the spool runs out of filament, the flag falls into the gap, blocking the light from passing through and triggering the sensor. **Components** - Opto-interruptor (PC4-M10 connector type) - Printed flag - 608 bearing - PTFE tube **Assembly Instructions** 1. Push the 608 bearing all the way into the provided opening in the lever arm, until it seats inside the opening -- the bearing should end about flush with the end of the opening. Using a vice is an easy way to accomplish this if you can't do it by hand. 2. Arrange the PC4-M10 connectors so that the plastic push-cap faces away from the spool on the line of filament travel, so the print head can't pull the PTFE tube out of position. **Notes** - Be careful, the printed flag is thin and fragile and easy to break (or to melt if you are using heat-shrink tubing). Go carefully if you need to attach an opaque cover to the little flag, and make sure that the flag can still easily fall into the gap in the opto-interruptor! - Note that operation of nearly any type of runout sensor depends on the filament freely leaving its spool when it runs out. Don't use filament brands that tape the end to the unreachable inside part of the spool (!) and make sure to clip off any bit of filament that may snag the spool at the end (you can usually reach the inside end of the filament through the hole in the center of the spool). **Wiring** - The cable and connectors provided with the opto endstop boards probably aren't long enough to reach to the controller board, so you'll have to extend them (using any gauge wire available). A wiring diagram for an MKS gen 1.4 board is shown in the illustrations. **Links for example parts:** - PC4-M10 connectors: https://www.amazon.com/gp/product/B01KHN1HWY/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 - Opto end-stop boards: https://www.amazon.com/BIQU-Optical-Endstop-Control-Printer/dp/B01FLSA47O/ref=sr_1_2?ie=UTF8&qid=1502728465&sr=8-2&keywords=optical+limit+switch