Proof of principle of a novel angular sensor concept for tracking systems

Lorenzo Iafolla, Lilian Witthauer, Azhar Zam, Georg Rauter, Philippe Claude Cattin

Research output: Contribution to journalArticlepeer-review


Robot-assisted and computer-guided minimally-invasive procedures represent a turning point in Minimally-Invasive Surgery (MIS) because they overcome significant limitations found in current state-of-the-art manual MIS procedures (e.g. imprecise motion, hand tremor, fatigue of the surgeon, limited workspace/maneuverability, etc.). Importantly, robotic systems can only reach the required high accuracy and precision when a tracking system with the corresponding accuracy and precision level for the surgical tool's end-effector enables closed-loop feedback control. Herein, we present a tracking system meeting the above required high accuracy and precision called ASTRAS (Angular Sensor for TRAcking Systems). In this paper, the working principle and performance of ASTRAS are presented and characterized respectively. ASTRAS is arranged in a way that a tilt of a mirror produces a shift of a shadow cast on an image sensor. Since the mechanical constraints between the light source, mirrors, shadow mask, and image sensor are known, the angle can be derived from the measured shadow shift. The working principle of ASTRAS allows the measurement of 2 degrees of freedom at once. Additionally, the commercial availability of small image sensors (∼1 × 1 × 0.5 mm3) allows implementing ASTRAS in the future as a down-scaled version in surgical tools such endoscopes. The characterization of ASTRAS was performed with an experimental setup evaluating the angular measurement performance in one degree of freedom. The results revealed a precision of ∼3·10−6 rad, a thermal stability of 1.9·10-5 rad/°C, a long term drift 10-5rad/day, and a linearity error of ∼10-4 rad. Future developments will focus on implementing a miniaturized prototype and making a chain of sensors to use in articulated devices.

Original languageEnglish (US)
Pages (from-to)390-398
Number of pages9
JournalSensors and Actuators, A: Physical
StatePublished - Sep 1 2018


  • Angular sensor
  • Medical tracking device
  • Rotary encoder

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering


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