Analysis methodology for a piezoelectric-driven optical tracker for ground-based interferometry

James H. Clark, F. Ernesto Penado

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations


We present our analysis methodology for a 20.3 cm prototype optical tracker to determine why instabilities occur below 50 Hz and suggest improvements. The Navy Precision Optical Interferometer makes use of six small optical telescope stations spaced along a Y-array to synthesize an equivalent single larger telescope. Piezoelectric-driven optical trackers steer 12.5 cm output beams from each station to an optics laboratory up to 700 m distant. A percentage of this starlight is split off and used in a closed-loop feedback to update the pointing of the telescope and steering of the tracker. Steering stabilizes atmospheric induced beam trajectory deviations, required for fringe generation. Because of closedloop feedback, we require all fundamental frequencies to be at least 3 times the desired operational frequency, or 150 Hz. These trackers are modified commercial aluminum gimbal mounts with flex-pivot axles and very small damping ratio. Steering is tip/tilt mirror rotation by push-only actuators and a return spring. It is critical contact be maintained between actuator, mirror mount and return spring. From our dynamic analysis, the 122 N return spring is 2.9 times that required, and has a natural frequency equal to 238 Hz. The range of steering, 140 microradian, is double that required and the 0.077 microradian precision is 2.6 times that required. The natural frequency of the tracker is 66 Hz and the tuned closed-loop operational frequency is only 22 Hz. We conclude the low fundamental frequency of the mount limits its performance below 50 Hz and stiffening the structure is required.

Original languageEnglish (US)
Title of host publicationOptical System Alignment, Tolerancing, and Verification VIII
EditorsRichard N. Youngworth, Jose Sasian
ISBN (Electronic)9781628412222
StatePublished - 2014
EventOptical System Alignment, Tolerancing, and Verification VIII - San Diego, United States
Duration: Aug 17 2014Aug 18 2014

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherOptical System Alignment, Tolerancing, and Verification VIII
Country/TerritoryUnited States
CitySan Diego


  • Frequency response
  • NPOI
  • Optical interferometry
  • Optical tracker
  • Piezoelectric actuator

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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