Engineering Projects/Easy Head Changer for 3D Printers

Project Head Changer
Create a mechanism to allow quick and easy removal and replacement of print heads from a 3D printer which: holds the head firmly in place, accomplishes electrical as well as mechanical connections, and provides feedback to assure proper operation. The long term goal is to automate the process.

Conceive
The problem with the original print head is that it is cumbersome to change and involves using a screwdriver to remove and replace screws, and tracing 4 sets of wires (going in different directions) to the circuit board to disconnect and reconnect them.

My objective was to create a mechanism that allows quick and easy removal and replacement of print heads from a 3D printer that:


 * Is relatively inexpensive to reproduce
 * Is simple, and will take no more than 2 to 3 steps
 * Aligns exactly where the previous print head was
 * Holds the head firmly in place
 * Accomplishes electrical as well as mechanical connections
 * Provides feedback to ensure proper operation

Design
Initially, to jump start my design ideas I began researching quick change options that have been successful in other applications. I actually found a blog that featured a 3-way Quick-fit Extruder, that fit into the Quick-fit X Carriage and locked down. What was important for my project was the fact that it had a universal adapter that you could attach various printheads to, slip it into a base, then turn a latch to secure it in place. It could be designed in a 3D software and printed using a 3D printer. I figured this would be the basis for my design. The design had some initial constraints because it needed to fit the original base footprint, and expand from there.

I researched several latching options, but eventually chose one that seemed to be perfect for the design, and could also be printed instead of purchased. I included an example in the first mock-up (cardboard).

Prototype 1
Next I focused on creating 3D models of the Quick Change base and adapter using Solid Edge, but found that to be challenging so I switched to SketchUp to further develop the design. The goal was to create a model that would seamlessly attach to the printer. In SketchUp, the design went through three more iterations before I had a model that I could fully test on the printer.

Prototype 2
The base and adapter fit together nicely, as designed, but when the model was compared with the printer there were several noticeable issues that didn't allow the prototype to fit on the printer. First, there wasn't enough space between the rear supports to fit around the back plate, so that space needed to increase. The rear screw insert cutouts were not spaced far enough apart and they needed to be notched out to fit in/around the back plate. The rectangles in the surface of the base for the side support arms were too small and needed to be widened. Also, I needed to create a way to attach the side support screws. There was too much vertical space between the adapter plate and the guide arms, so I had to reduce that to create a more snug fit. I also needed to increase the diameter of the screw head inset in the adapter plate so the screw could sit properly in the plate. Finally, I needed to create ramps on the guide arms so the insertion of the adapter plate into the base is smoother.

Prototype 3
This is the reworked design.

...with small tab-stops added on the guide arm to help hold the adapter plate in position once it is slid into the base.

When compared with the printer, this model actually fit well. I was able to successfully attach the Quick Change Base to the printer supports. What needed to be addressed next in the design was how to incorporate the electrical connections. Brandon was able to secure 15-pin D-sub connectors for the electrical connections, which worked great for our purposes. He was able to solder the connections to the paste extruder and test it with an arduino...it worked, so I began redesigning the Quick Change to incorporate the D-Sub connectors.

Prototype 4
My first solution for incorporating the D-sub's was to put it in the side of the base. This was the simplest option, and would require minimal changes to the model in SketchUp. Also modified the male D-Sub for a smoother connection.

Upon further consideration it was determined that it would be better to attach the printhead in one motion...setting the printhead in place and making the electrical connection at the same time. I then sketched a design where the D-subs were incorporated on the underside of the base (left and right), and on the new, modified adapter sled. I added the modifications for the D-subs to the design in SketchUp, as well as a place to mount the fan, and to route the electrical wires. I also increased the depth of the v-shaped recesses for the side screws.

Prototype 4 Print
With the models cleaned up, I was able to attach the two 15-pin D-subs (male & female) to the base and adapter, then connect them. Everything lined up as intended.

Implement
I began by cutting the wires connecting the stepper motor, fan, and extruder nozzle to the printer, then used the soldering iron to connect them to the D-Sub connectors for the base and adapter.


 * Attached the print head to the adapter plate, and secured the D-subs.


 * Attached the new base to the printer, and secured the D-Subs.
 * Connected the print head adapter to the base.
 * Organized the wiring from the base to the circuit board.

Parts
In addition to the PLA used to print my parts from the MakerBot Replicator 2 I used: All other parts, screws & nuts, used to attach the base and adapter were already part of the printer hardware. (5 each on the base and 2 each on the adapter.)
 * 2 -- 15-Position male D-Sub connectors (This could potentially be replaced with a 9-Position D-Sub)
 * 2 -- 15-Position female D-Sub connectors (This could potentially be replaced with a 9-Position D-Sub)
 * 8 -- #4-40 x 1/2" machine screws w/nuts (4, used on the base) to attach D-Subs)
 * 1 -- 12VDC 0.13A 1.56W DC Brushless Fan, 40 mm x 40 mm x 10.2 mm (only used with a heated nozzle)
 * 2 -- Additional screws to attach fan

Operate
This particular printer work with a software called Pronterface. I had to downloaded and install Pronterface on my Mac from a link on the RepRap Wiki page (see below). Initially there were errors recognizing the printer. I kept getting an error dealing with the baud rate, but I was able to increase the baud rate and enter the refresh code "M999" which caused the printer work. I was then able to move the printhead along the x and z-axis, as well as heat up the nozzle. There was a problem though because the nozzle didn't retain the desired temperature. It would heat to the set temperature point, but would decline after that….it wouldn't hold consistent at the desired temperature.

The next thing to test was the printhead stepper motor and it's ability to extrude. It was set to extrude at 5.0 mm @ 100 mm/min, but when I selected extrude I kept getting an error that read 0. Like there was no filament in the printer. I eventually reentered the "5.0" mm then selected "Extrude" and it began to work.

During Project Day presentations I was able to set up the printer and get it working…partially. The printer nozzle was able to heat up and hold the set temperature for a longer period of time, but after awhile it still began to decline and I couldn't stop it. I did notice that whenever the heated extruder was disconnected from the base it caused an error in the software, and needed to be refreshed after the head was reconnected. When the paste extruder was attached it didn't work at all. I kept getting an error about the extruder not being connected. Need to determine what is causing the error. May need to do some reprogramming.

I wasn't able to test the full functionality of the printer after adding the Quick Change.

Future Next Steps:

 * Secure wires from nozzle
 * Troubleshoot/determine why the heat is not being maintained
 * Incorporate functionality that communicates a proper install of print heads
 * For heated nozzles, construct mechanism to retain heat for quicker start-up
 * Automate print head change

Sources:

http://www.reprap.org/wiki/Printrun

http://koti.kapsi.fi/~kliment/printrun/