# Design and Analysis: Servo-Tube-Powered Liquid Jet Injector for Drug Delivery Applications
###### Abstract
AC current is converted to DC using a bridge rectifier, and the DC current is then fed to six internal gate bridge rectifiers (IGBTs), which act as high-speed switches. The switching of the IGBTs is controlled via a microcontroller within the drive at a maximum frequency of 16 kHz and utilizes a space vector modulation (SPVM) algorithm in order to obtain a three-phase AC waveform with the desired amplitude and frequency. The microcontroller also receives a desired motion profile, and the feedback from the sinusoidal encoder in conjunction with a PID loop will ensure the required motion ensues. In this study, the Compax3 is used in position control mode, whereby a finite series of pulses are sent to the drive at a predetermined frequency. The pulse train sent to the drive must adhere to industrial standards and therefore have a maximum amplitude of 24 volts, with a maximum frequency of 500 kHz. The drive then utilizes an internal map to correlate each rising edge of a pulse with a fixed linear distance of the actuator rod's pole pitch. The sinusoidal encoder provides real-time feedback of the actuator rod's displacement, and a PID loop ensures that motor windings are energized appropriately to compensate for any following error (Parker Hannifin Corp. 2013). The exact values of the parameters used in the PID loop were established after consultation with Dunkermotoren and optimized experimentally. This was accomplished using software provided by Parker (C3 servo Manager), whereby the system was tested under experimental load and optimized to decrease following error whilst maintaining stability of the PID loop. The parameters depicted in Table 3 represent the final tuning of the actuator. Tuning was performed by applying an oscillatory step response to the system at a speed of 4 m/s and a distance of 20 mm and then utilizing an oscilloscope to track the actual position, commanded position and following error versus time. The PID parameters were modified until minimal overshoot, minimal flowing error and good vibration suppression about the target destination were achieved. Figure 1 below demonstrates both the actual position and the flowing error. The time division on the horizontal axis is set to 400 ms, and the divisions for the error and position are 5 increments and 1000 increments, respectively. As is normal with a step response input to a PID loop, a maximum deviation of 8 increments (80 \(\upmu\)m) is observed; when the relative motion is commanded, the plunger deviates from its real-time target, but the error is recuperated in a timely manner. The tuning performed on the PID ensures that, when the actuator is coupled to the injector head, the plunger will follow its outlined trajectory with \(+/-\) 20 increments, irrespective of the changing factors, such as friction, nozzle size or fluid viscosity. This will greatly simplify modeling the output pressure of the device, as the only relationship that needs to be considered is that of the pressure increase in the injection chamber as a function of plunger displacement. \begin{table}
\begin{tabular}{l l} \hline \hline  & **Specification** & **Value** \\ \hline Power Input & 253 V.AC @ 60 Hz/50 Hz \\ Input Phases & 3 \(\mathcal{O}\) \\ PWM Switching & 16 kHz \\ Continuous Current Output (RMS) & 15 amps \\ Peak Current Output (RMS) & 30 amps \\ Commutation & Sinusoidal \\ Velocity Loop & 125 \(\upmu\)s \\ Position Loop & 125 \(\upmu\)s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parker Compax3 T10 Drive Specifications (Parker Hannifin Corp. parkermotion.com, accessed on 1 May 2022). The objective of this study is to design and manufacture a prototype liquid jet injector that can provide a platform capable of shaping the real-time jet injection pressure profile to adapt to different drug delivery needs.