Abstract:
Needle-free jet injection allows delivery of liquid drugs through the skin in the
form of a narrow fluid jet traveling at high speed, minimizing the risk of accidents.
The use of a controllable actuator to drive this process has many advantages, but
the voice coil actuators previously used for this purpose are too large and heavy for
practical use with common injection volumes (1 mL). Linear synchronous motors, on
the other hand, promise significant mass reduction for future portable jet injection
systems.
In this thesis, the requirements on linear synchronous motors were examined
and tailored to selecting a linear synchronous motor design capable of delivering
1 mL jet injections in the form of a clinically appropriate injectors. The types of
linear synchronous motors included Permanent Magnet Linear Synchronous Motor
(PMLSM), Linear Flux Switching Motor (LFSM), and Linear Transverse Flux Motor
(LTFM).
Two modelling approaches for linear synchronous motors were developed: A
semi-analytical solution for Harmonic Modeling for PMLSM; and a Response Surface
Modelling method, powered by Artificial Neural Networks for PMLSM, LFSM,
and LTFM. Both Harmonic Modeling and Response Surface Modelling were found
to have very similar modeling results. All three types of motors were optimized to
the same set of requirements previously engineered with minor adaptations. PMLSM
was found to be the best performing type of motor in this case study.
A final prototype motor design was determined using an optimization scheme
for finding the lowest motor mass at a fixed power dissipation, and an automated
routine for estimating the cogging force using finite-element analysis. A prototype
motor was constructed, with a nominal mass of 322 g, a stroke of 80 mm, and a
target operating power of 1.2 kW; experimental data show that the motor constant
is within 10% of the target, and that the cogging force is in close agreement with the
model. Test ejection of water into a force sensor and porcine tissue verified that the
motor is fit for delivering 1 mL needle-free injections.
The design methodology explained here shows the benefits to integrated design
optimization of both the actuator and the load, particularly in systems that drive
fluid pressure loads, and also opens the door to controllable injector designs for
larger volumes.