A Linear Permanent Magnet Synchronous Motor for Large Volume Needle-Free Jet Injection

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 are too large and heavy for practical use with common injection volumes (1 mL). We instead propose a compact slotless tubular linear permanent magnet synchronous motor design for jet injection. The design was determined by utilizing a semi-analytical electromagnetic modeling technique to predict the performance of any given motor design, an optimization scheme for the motor mass at a given power dissipation, and an automated routine for estimating 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 verified that the motor is fit for needle-free injection. 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.