3D BioPrinter

Initial MEchanical design

The initial challenge was to design a mechanism that can lift the print head with precision and accuracy while taking up as little space as possible. Several types of mechanisms were considered, including a servo operated rack & pinion system.

Time was also a factor because I could only work as a GRA for the duration of my robotics degree and the printer had to be functional before work could begin on the next phase of my research, the bioreactor.

Joe and I went to Hyrel to discuss their previous ideas for a similar system. Karl, the CEO, was kind enough to gift us two Misumi LX30 linear ball screw assemblies, sans motors. I was able design the system around these by creating a special mounting plate between the truck and the linear rail of the print head and by making a simple mount for a NEMA 11 stepper motor to drive the screw. The LX30 mounted to the back of the modified gib from the SDS 5. This assembly was able to mount to the printer by the same method as the original print head. 

I milled the truck and motor mounts from aluminum.

Electronics Design

Once the early prototype of the mechanism was built, the next step was to develop the electronics and actually make it run.

The System 30M printer that we were working with was an older model that had been previously scavenged for parts and abandoned in a dark corner somewhere. Joe, having worked at Hyrel, was in charge of getting the machine up and running again. I was developing the print head lifting system while he did that. He and I discussed the possible methods of driving the actuator. 

One of the defining features of Hyrel printers is their ability to mount multiple, interchangeable tool heads of varying types and functions. Because of this, each print head slot has electrical connections for extruder motors, fans, lights, and more. Since the SDS 5 print head only uses a single motor, the 12v auxiliary power supply and the cooling fan connections were not used. I was able to take advantage of that. The SDS 5 circuit board has passthrough connections for these.

I used the auxiliary 12v supply to power the Head Lifter control board and motor and to use the fan signal to activate it. This allowed us to control it with a simple line in the GCODE. It lowers when the fan signal is high and raises to its home position when the signal is low.

The next step was to select the necessary components. I needed a versatile and compact microcontroller that could handle a screen, several inputs, and run a stepper motor. I picked the Seeeduino Xiao ESP32C3 and programmed it using micropython.  For the initial prototype, a relay was used to detect the fan signal. For positioning, a hall effect sensor was used. The hall effect sensor gives a signal when it detects the magnetic field from a magnet mounted in on the linear rail. The travel distance can be adjusted by three buttons and the display screen. The Head Lift controller sends motion control to the stepper motor via a stepper motor driver. The 12V auxiliary supply feeds the stepper motor driver, and a buck converter that steps the voltage down to 5V for the microcontroller. 

This system functioned, but the controller enclosure was clunky and prone to faulty connections. It was also difficult to see and adjust, given its location. The range of motion along the Y-axis was also limited by the size and placement of the enclosure. Despite its flaws, it was a successful proof of concept.

The next design featured a transistor in place of the relay and was incorporated into a custom circuit board. I used EasyEDA to design the board and had them manufactured by JLPCB. 

Final Mechanical Design

 The custom PCB needed to be mounted, so as I was designing it, I also redesigned the top of the extruder assembly again to accommodate it. 

Results

 The system worked beautifully! We loaded the syringes with petroleum jelly and three different colored collagen solutions. The modifications to the printer worked perfectly during every test. The resulting media is shown below.