# Design and Analysis: Servo-Tube-Powered Liquid Jet Injector for Drug Delivery Applications
## 2 Materials and Methods  
### Prototype Device Specification  
In order to produce the required liquid jets for experimental analysis, an injection chamber, a small-diameter plunger and a nozzle must be added to the actuator. The injection chamber is fitted to the servo actuator by utilizing an adapter block that mounts directly to one of the stator's end caps. This ensures concentricity between the actuator and the injection chamber. Furthermore, in this manner, the device can be used for future works, and different injection chamber geometries can be studied and verified for performance. The prototype consists of an injection chamber with a 6.35 mm bore that is terminated by a thread that receives a nozzle. The orifice-type nozzles manufactured by O'Keefe used in this experimental device have successfully been used in previous studies [25; 54] to obtain confined jets with minimal divergence. This study will evaluate the performance of the device in shaping pressure profiles utilizing four different nozzles outlined in Table 4.  
Figure 1: Following error as a function of displacement.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Specification** & **Value** \\ \hline Pulses Per & 1000 cm \\ Permissible Deviation & 20 increments \\ Actuator Rod Weight & 1.310 kg \\ Stiffness Gain & 200\% \\ Damping Gain & 40\% \\ Mass Inertia Gain & 60\% \\ Velocity Feed Forward Gain & 100\% \\ Acceleration Feed Forward Gain & 100\% \\ Current Feed Forward Gain & 100\% \\ Tracking Error Filter & 50 us \\ \hline \hline \end{tabular}
\end{table}
Table 3: PID Loop Relevant Parameters.  
The injection chamber also contains one threaded port, which serves as a filler inlet, in order to recharge the chamber with fluid. The injection chamber also houses a plunger with an O-ring sealed tip, see details in Table 5. It is important to note that, when the plunger is clear of the filling port, the size of the bore is increased to allow air to vent as the chamber is filled. The plunger is coupled to the actuator rod through a threaded coupling. The stator end cap on the opposing side of the injection chamber is capped by a block containing an OMRON D5A limit switch capable of 3 \(\upmu\)m precision. The limit switch will enable the precise referencing of a home position, from which absolute measurements can be applied. Figure 2 illustrates how these individual components are coupled together to produce the injector.  
In order to accurately gather pressure traces, the experimental prototype is fitted to a specially designed stand, as shown in Figure 3. This stand makes it possible to mount the injector in a vertical position and provides fine positioning of the injector height so that the standoff distance can be adjusted and accurately maintained upon subsequent runs. The stand weighs 75 kg and is constructed from a 12.7 mm thick plate; this provides the necessary stability to cope with the forces generated by the servo-tube actuator.  
\begin{table}
\begin{tabular}{l c} \hline \hline  & **Nozzle Number** & **Orifice Diameter (\(\upmu\)m)** \\ \hline
6 & 150 \\
8 & 200 \\
10 & 250 \\
12 & 300 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Nozzle specification.  
Figure 2: Schematic of complete servo-tube-driven injector.