Cable-Driven Tool Changer System

thingiverse

Update! This version has now been superseded by a more mature [version 2](https://www.thingiverse.com/thing:3805144). I will leave this one up for reference, though. [Demos for the curious!](https://youtu.be/yCwlqF1J5I8) Long-form writeup can be found [here](http://www.doublejumpelectric.com/projects/toolchanging_pen_plotter/2019-03-17-toolchanging_pen_plotter/). Let's kick things off with a quick video summary of the [tool changer](https://youtu.be/ibJpjYAcjaM) and [parking post](https://youtu.be/QcsXqRd0ouY). And let's throw in some quick [repeatability testing](https://youtu.be/TebSZKkX770) for good measure. Note: CAD files on this project are finished, but full integration onto my 3D printer is still a work-in-progress. This project is a complete solution for tool-changing, including * a highly-repeatable tool locking/unlocking mechanim * a generic tool base with reliable geometry for parking that can be adapted to many tools such as 3D printer extruders, pen holders, inspection cameras, etc. * a generic parking post This tool-changing system has been my labor of love. Here's a quick feature breakdown. ## Features: * Attaches directly to an MGN9H carriage block like [this one](https://motionconstrained.com/store/hiwin-linear-guides/hiwin-mg-series-linear-guides/new-hiwin-mgn9h-linear-guides-mgn-series-linear-bearings-30mm-to-1190mm-long/) * Easy to print. (No overhangs or crazy geometries) * small number of printed parts. The tool-changer is only 7 printed parts! * Highly repeatable using a kinematic coupling based on off-the-shelf parts * no magnets * easy to source parts for. * generic. The base tool platform can be easily scaled to a variety of tools ## How it Works "in Theory" The toolchanger uses a kinematic coupling to connect and disconnect tools. The result is that a tool is located onto the carriage with (in theory) exactly 6 points of contact. Coupling in this fashion is extremely repeatable. In fact, machined variants of this type of coupling have sub-micron repeatability. I haven't quantified mine, but I'd expect it to be within 50 microns. The tool get's picked-up and locked-in using a T-shaped lock and a 3D-printed wedge feature. The wedge feature lives on its own part and can be replaced when it wears out. For the most long-lasting results, I suggest using a stepper motor driver with stall detection to detect when the motor is locked, although if you can't do this, simply dial down the motor torque setting until it's just enough to lock the tool. Part of what makes this mechanism so reliable is that, while it's 3D printed, the actual mating surfaces are either steel or stainless steel. In this case, the coupling is made from 3 steel balls, which live on the tool holder, and 6 shoulder screws, which live on the carriage. This concept of mixing-and-matching stock parts with printed parts is what I call "functional printing," but the idea comes back from the days of RepRap, when nuts-and-bolts of their mostly-printed printer were called "vitamins." We're living in a marvelous age where mass-manufacturing has made stock parts pretty ubiquitous. (Heck, even Amazon.com sells a giant hoard of machine screw types along with bearings, bushings, and other precision motion components.) I'm hoping to see more of us take advantage of this hybrid approach to 3D printed projects, so I'm here to showcase this idea at its best. ## Drawbacks: Nothing's perfect. Here's a couple of minor issues. * One machined part, although, with some hacks, you could print this part too.. * Most stock parts come from McMaster-Carr, which does not ship worldwide. * Many more parts compared to simply one 3D-printed part. Nevertheless, I use these parts all the time, so there's no shame in having a few in baggies in the lab. * Needs software. (Suggestions welcome!) I love progress pictures! If you do too, here's my progress-log [here](https://www.flickr.com/photos/77947059@N05/albums/72157697745453260) # Shopping Lists For all the parts you can't print, here's a breakdown sorted by subsystem ## Tool-Changer: * 1x NEMA 17 motor like [this one](https://www.amazon.com/gp/product/B00PNEQ79Q/ref=ppx_yo_dt_b_asin_title_o08__o00_s00?ie=UTF8&psc=1) * 2x Spring Guide cut to desired length. [SG-088-020-120](http://stocksprings.drtempleman.com/item/spring-guides/spring-guide/sg-088-020-120) is sold as one 120-in. cable, but it can be cut with hard wire cutters. (Bicycle brake cable will NOT work.) * 2-meters control cable. Either [0.56mm Spectra Line](https://www.amazon.com/gp/product/B003ZZ8DWE/ref=oh_aui_search_asin_title?ie=UTF8&psc=1) or [1/32-in Steel Cable](https://www.amazon.com/gp/product/B0013HEOA6/ref=oh_aui_search_asin_title?ie=UTF8&th=1) will work * 1x sleeve bearing [2938T1](https://www.mcmaster.com/2938t1) * 3x M3 Heat-set Inserts [94180A331](https://www.mcmaster.com/94180a331) * 6x M3 shoulder screws, 4mm diameter, 12mm length [90265A122](https://www.mcmaster.com/90265a122) * 2x M3 screws, 6mm length, [92095A179](https://www.mcmaster.com/92095a179) * 6x M3 flathead screws, 6mm length [92125A126](https://www.mcmaster.com/92125a126) * 1x M3 set-screw, 4mm length [92605A098](https://www.mcmaster.com/92605a098) * 1x dowel pin 3.175mm diameter, 12.7mm len [97325A380](https://www.mcmaster.com/97325a380) * 2x wheel hub, 5mm bore, M3 holes. 2-packs sold from [Pololu](https://www.pololu.com/product/1998) * OPTIONAL Nylon sleeving 0.25-in. [Amazon](https://www.amazon.com/gp/product/B074GM1PK1/ref=ppx_yo_dt_b_asin_title_o07__o00_s00?ie=UTF8&psc=1) * OPTIONAL heat-shrink tubing (8mm len) ## Tool Base: * 3x "Kossel-style" 10mm threaded balls with M4 threads like [these](https://www.newegg.com/Product/Product.aspx?Item=9SIA6RP6KB3392&ignorebbr=1&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC-_-pla-Alexnld-_-3D+Printers+Accessories-_-9SIA6RP6KB3392&gclid=Cj0KCQiAj4biBRC-ARIsAA4WaFhLvXvss8rNGhMRVsrAPycqDwCeyswcbwuWq3SPxSJ2l5NPRcVrLVkaAhbHEALw_wcB&gclsrc=aw.ds) * 3x M4 buttonhead screws, 10mm length [92095A190](https://www.mcmaster.com/92095a190) * 3x M3 flathead screws, 8mm length [92125A128](https://www.mcmaster.com/92125a128) * 4x M2 screws, 6mm length [91292A831](https://www.mcmaster.com/91292A831) * 3x M3 Heat-set Inserts [94180A331](https://www.mcmaster.com/94180a331) * 4x M2 Heat-set Inserts [94180A307](https://www.mcmaster.com/94180a307) ## Tool Parking Post: * 2x dowel pins, 5mm diameter, 50mm long [91585A581](https://www.mcmaster.com/91585a581) (McMaster-Carr sells 10-packs) # Print Settings All prints were tested with my Prusa i3 Mk3. Print all parts in the rendered orientation! I make not guarantees about part performance if printed otherwise. Good news, though: none of these parts require any support material! ## Tool Changer Base * 0.2mm layer height * 6 perimeter layers * 80% honeycomb infill * PLA (ABS probably ok too) * Brim recommended ## Shoulder Screw Reinforcement Plates You can laser-cut these parts too from 0.0625-in. Delrin. Use the attached PDF file to do so. * 0.2mm layer height * 4 perimeters * print solid. (They're tiny.) * PLA (ABS probably ok too) * Note: you may need to drill out the larger two holes to 3mm to fit the shoulder screws. ## Cable Drive Motor Post Vertical * 0.2mm layer height * 4 perimeters * 20% rectilinear infill (more is ok too) * PLA (ABS probably ok too) ## Pulleys * 0.2mm layer height * 4 perimeters * 20% rectilinear infill (more is ok too) * PLA (ABS probably ok too) ## Pulley Cinch Backing * 0.2mm layer height * 6 perimeter layers * 20% honeycomb infill (more is ok too) * 3mm raft highly recommended * PLA (ABS probably ok too) * Brim recommended ## Alignment groove disc * 0.15mm layer height * 4 perimeter layers * 20% rectilinear infill (more is ok too) * PLA (ABS probably ok too) ## Generic Parking Post Base * 0.2mm layer height * 4 perimeters * 20% rectilinear infill (more is ok too) * PLA (ABS probably ok too) ## Tool Base Flexure * Laser-Cut from 3.175mm (0.125-in.) Delrin * PDF has been pre-offset by 0.0762mm (0.003-in.) to account for the width of the laser spot size