Final Design
Flow Chemistry System
The final design of the system consists of the following components: the system's graphical user interface, the modular syringe holder, the servo motor refill mechanism , the corrosion-resistant stainless steel threaded rod, the electronics box and the touchscreen stand.
Nextion Graphical User Interface
The graphical user interface was designed using the Nextion Editor software for the 7.0" Nextion Intelligent Series HMI Touch Display with enclosure. This display was chosen because the program editor makes it easy to design a graphical user interface (GUI) by simply dragging in components such as buttons and sliders onto the interface screen being designed.
The user interface was designed in a way as to be user friendly and to provide a way to control every aspect of the syringe pump solely with the interface. To do this, the user interface together with the Arduino were programmed so that the user can input syringe parameters into the system such as syringe size (mL), syringe inner diameter (mm) and current volume inside the syringe (mL). Then the user is able to set the pump parameters: flow direction, flow rate and volume to either dispense or withdraw. After setting all these parameters the syringe pump is ready to run.
Video walkthrough of setting up 2 syringe pumps for flow chemistry experiment.
Modular Syringe Holder
Under the Croatt Research Group's design the syringe holder in the system only supports one size of syringe at a time. The user must replace the holder every time if they wish to change the syringe size. We wanted to eliminate this issue, so we designed a new modular syringe holder that can hold all the different standard syringe sizes (1, 3, 5, 10 mL) without the need to swap any parts.
Modular Syringe Holder
Automated Refilling
Once the syringes are loaded into the system with all the tubing, there needs to be a way to refill the syringes as it can be quite cumbersome to disconnect everything just to refill the syringe again. One way is to use check valves in the tubing network. Check valves only allow fluid flow in one direction, so a valve would be needed for both the fluid coming in to refill the syringe and one for the fluid coming out from the syringe. With the valves, the fluid pushed out of the syringe would not be able to go back and the syringe would not be able to push fluid into the refilling tube. The problem with this is that check valves are incredibly expensive. Thus, we want to find an alternative cheaper way to refill the syringe.
One method, used in the Burkart lab, is using a 3-way stopcock to control where the fluid will flow. Essentially, the stopcock will only allow for a connection between two tubing pathways. This means that when refilling the system would only be connected to the refilling tube and when pumping out, the system will only be connected to the output tube. This is a much cheaper solution, and the process can be automated with a servomotor to turn the valve and switch the connections. When the syringe is nearly empty (at an upper or lower limit position), the servomotor will swap the connection and the syringe will be driven in the reverse direction.
Servo Motor Refill Mechanism
Corrosion-Resistant Stainless Steel Rod
As this syringe pump system will deal with a lot of chemicals and reactions under a fume hood, it is important that the key components of the system are resistant to corrosion from chemicals such as ozone. The overall chassis of the system is 3d-printed and would be composed of plastic so it would generally be resistant to corrosion. However, some of the other key parts of the system are composed of metal, like the lead screw mechanism used to push the carriage block. As such, the threaded rod in this mechanism needs to be of a suitable material to withstand chemicals. After some research, we found that 316 Grade stainless steel to be the best option for our system as it very inexpensive and holds up to chemicals very well. So, we fitted most of the metal components in our system to be made from 316 Grade stainless steel.
Electronics Box and Touchscreen Stand
The electronics containment box is intended to house all of the electrical components excluding the power supplies. The box is intended to protect the electrical components from any liquid and chemicals in the lab. The power supplies are kept outside of the box due to heating concerns. A stand for the touchscreen was also purchased to hold up the touchscreen.
Electronics Box
Inside of Electronics Box
Touch Screen Stand
How the Flow Chemistry System Works
The control system, as pictured below, consists of a Nextion graphical user interface which is able to send commands to Arduino via its serial monitor. From those commands the Arduino microcontroller is able to control the speed and position of the stepper motor which are the two most important variables for controlling the system. The speed of the motor is directly related to the flow rate which is the volume of liquid that is either dispensed or withdrawn by the syringe pump per unit of time. While the position of the motor relates to how much volume is dispensed or withdrawn by the pump since each rotation of the motor moves the carriage pusher blocker together with the syringe plunger approximately a distance of 1.27 mm.
