Closed-Loop Actuator Control for Cochlear Surgery: Lessons from the Lab
PWM, potentiometer feedback, and the ±2 mm tolerance that decides whether a control loop is honest.
I joined a PhD project at Brunel working on robot-assisted cochlear implant insertion. The brief was simple to state and humbling to implement: move a linear actuator slowly, smoothly, and predictably, because the patient is the load.
The hardware loop
Actuonix L12 actuators, driven by PWM from an Arduino, with the built-in potentiometer providing position feedback into MATLAB. The control loop reads target position, samples actual position, computes error, and adjusts duty cycle.
Why velocity is harder than position
Position is straightforward. Velocity is where the safety story lives. We investigated the current–resistance–velocity relationship so the same actuator could be commanded to insert at a controlled speed rather than just stop at a controlled depth.
Communicating across disciplines
Most of the team are not software engineers. UML activity diagrams of the control flow turned out to be the most valuable artefact I produced — more than the firmware itself.
Safety-critical code earns its name in the documentation, not just the binary.