Oct 14, 2022

Public workspaceDeriving steps per mm for an LVE system V.1

DOI
https://dx.doi.org/10.17504/protocols.io.ewov1o8jplr2/v1
  • Robert Jess1,
  • Jonathan Widdowson1,2,
  • Feihu Zhao1,
  • Christopher Wright1
  • 1Swansea University;
  • 2Procoll Ltd
Robert B Jess
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DOI: https://dx.doi.org/10.17504/protocols.io.ewov1o8jplr2/v1
Protocol Citation: Robert Jess, Jonathan Widdowson, Feihu Zhao, Christopher Wright 2022. Deriving steps per mm for an LVE system. protocols.io https://dx.doi.org/10.17504/protocols.io.ewov1o8jplr2/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License,  which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: In development
We are still developing and optimizing this protocol.
Created: September 20, 2022
Last Modified: October 14, 2022
Protocol Integer ID: 70293
Keywords: 3D Bioprinting, Bioprinting, LVE, Steps, Stepper Motor, Software, Firmware, Control, Syringe pump, Mathematic, source syringe pump hardware, accurate control of the syringe pump, 3d printer, source syringe pump, cost laboratory 3d bioprinter, 3d printer system, large volume extruder, syringe pump, bioprinter, 3d printer electronic, shelf fused filament fabrication, fused filament fabrication, steps per mm, rich control over the 3d printer system, fff printer firmware, extrusion, lve system modification
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Abstract
Modification of off-the-shelf fused filament fabrication (FFF) 3D printers with a syringe pump, used as a large volume extruder (LVE) is a common method for the creation of low-cost laboratory 3D bioprinters. Open-source syringe pumps with accompanying firmware exist, however they require researchers to choose accurate control of the syringe pump over rich control over the 3D printer system. The combination of open-source syringe pump hardware controlled with 3D printer electronics and firmware gives the best of both worlds, however this firmware is not designed to control fluids, consequently some parameters may need to be calculated differently. FFF printer firmware (such as RepRapFirmware) uses E-steps-per-mm to translate the movement of the stepper motor into the extrusion of filament pre-nozzle. This method finds the value of this parameter for a bioprinter with a bowden-tube based LVE.
Guidelines
This method is for an LVE that is based around the MOST Open Source Syrigne Pump [1], or similar syringe pumps such as the Poseidon from Patcher Lab [2], connected to the printer carriage and print head via a bowden tube.

[1] Joshua M. Pearce, Bas Wijnen (2016). "Open-source syringe pump". Appropedia. Retrieved October 13, 2022.
[2] A. Sina Booeshaghi, Eduardo da Veiga Beltrame, Dylan Bannon, Jase Gehring and Lior Pachter, "Principles of open source bioinstrumentation applied to the poseidon syringe pump system", Scientific Reports 9, Article number: 12385 (2019)
Materials

Equipment
Open Source Syringe Pump
NAME
Syringe Pump
TYPE
MOST OSSP
BRAND
n/a
SKU
https://www.appropedia.org/Open-source_syringe_pump
LINK

Troubleshooting
Take measurements
Take the following measurements:

Required
Thread Pitch (mm)
Required
Thread Starts
Required
Internal radius of the syringe (mm)
Required
Internal radius of the bowden tube (mm)
Required
Motor Steps
Required
Micro-Stepping


Finding the thread's lead
Most lead screws are single start, and the one recommended in the MOST OSSP is single start, this means that the lead (the distance the carriage travels with one rotation of the lead screw) is equal to the pitch (the distance between the crests of the thread).

If you are using a multi-start lead screw the following formula should be used to calculate the thread's lead:

Deriving the revolutions per mm
The ratio between the syringe and the Bowden tube can be calculated as follows:

Where is the distance travelled by the syringe plunger, is the resultant distance the gel travels through the bowden tube, is the internal radius of the syringe, and is the internal radius of the bowden tube.

The ratio between the motor and the syringe is equal to the ratio between the motor and the linear distance travelled by the syringe plunger is:


From this we know, when ls = lead, the ratio between the lead screw and the Bowden tube, is:

This makes the revolutions per mm:






Finding the E-Steps-per-mm
Multiply the motor steps by the micro-stepping by the length of filament produced through thr bowden tube with one revolution of the stepper motor