Difference between revisions of "Team:Grenoble-Alpes/pipetting module"

In our system, we need to pipette automatically different volumes to execute our biological process.

The solution we chose is to use an electronic pipette Biohit e10. The main advantage is that after removing the cap of the pipette, we can solder wires to the electronic card to control the different buttons of the pipette and it will work by itself!

The button functions are described in the following figure:

To make the pipette work, we need a power supply of 5 Volts and 1.5 Ampers at least. Wires are connected from an Arduino card (microcontroller) to the buttons to control them later.

We needed a pipetting system moving vertically above the samples on the circular plate. For that, we used a linear guide with a lead screw and a motor allowing to move the pipette vertically with a good precision. All the pieces, like the guiding bars, the coupler and the lead screw have been bought on a professional website [2] to guarantee us a fluid and precise movement. It provides the precision required to pipette at the wanted depth in the Eppendorf tubes. The precision reached is about one-tenth of mm.

This linear guide system has been fixed on a wooden plate between two aluminum bars. The plate has been first engraved with a laser-cutting machine to mark the positions to drill the holes for the screws at the right position.

The vertical movement of the pipette is realized by a motor controlled with an Arduino microcontroller.

We printed a piece in 3D to hold the pipette and to fix it to the linear guide.

A piece designed on a Computer-Aided Design (CAD) software and printed 3D is fixed on the linear guide and holds the pipette. The dimensions have been measured carefully to fit perfectly with the pipette. Some foam rubber is added to get a better fixation of the pipette with higher pressure forces.

One issue of this system was to take a pipette tip on the circular plate with the pipette. The pipette had to go down, insert in the tip and push a bit to attach. However, the force required to push was too strong and instead of inserting in the tip, the pipette was detaching from the 3D-printed holding piece. This problem was solved by drilling a hole at the back of the 3D-printed piece. With a screw passing through this hole and nuts, the pipette is now perfectly fixed.

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In the first stage of the project development, we thought of 3 main ideas to realize the functions of the pipetting module.

A simple syringe, whose piston is connected to a motor.

The use of a simple syringe with a motor pulling or pushing the piston has the advantage of being an affordable solution. However, we cannot control how much we really pull or push the piston with our motor: if our stepper motor misses a step, it would be very difficult for us to notice it. Hence, there is no repeatability of the biological process possible.