Dynamic Performance of Vibrometer Steering System for Dynamic In-Fight Tracking and Measurement

Noncontact dynamic measurements of lightweight flexible aerospace structures in motion present several challenges. Achieving high frequency and high resolution measurements requires multiple registered metrology systems. Many noncontact measurement methods are based on the object staying aligned with the sensor. Yet sometimes the desired loading is a result of the motion interacting with structural dynamics as is the case with aeroelasticity. Triangulation of video data can capture large scale motion, but limits the speed and resolution of the measurement. Laser vibrometry can capture minute structural vibrations but assumes vibrations about an equilibrium point. This paper presents a method of registering a laser vibrometer steering system to a motion capture system to produce dynamic in-flight tracking measurements (DITM). The basis of the calibration lies with determining the location of the laser steering system through the videogrammetry capture volume for DITM. A method for using video capture of the laser is presented to determine 3-D lines through the capture volume that are used to determine origin of laser with respect to the video system. Results of the calibration are sufficient to have the laser track within half a degree for distances over 4m. The laser is then able to be open-loop steered with static and dynamic accuracies presented. Initial dynamic accuracies were insufficient, so a Kalman filter was incorporated to estimate the target’s current position. This system can provide real-time structural awareness enabling active control. Vibration tests were also conducted to ensure the system did not produce any significant noise or shift in frequency data using tuning forks. The vibration data was captured under different conditions and compared to a baseline signal. For each case tested there was no change in frequency but the signal amplitude was noticeably affected by directing the laser through the mirrors.