Calibration of an electro-mechanical shutter: dynamical effects

Photometric measurement with a CCD camera by means of an electromechanical shutter, are possible only if the trajectory and velocity of blades during motion in front of the CCD are dully characterised and repeatable according to the requirements. The aim of the present work is to describe the numerical and experimental characterisation, emphasising the obtained results. In the characterised shutter each blade is mounted on a four bar mechanism driven by a dedicated torque motor. A high resolution encoder was integrated on each motor shaft. The transfer function between the encoder output and the blade position has been evaluated by means of a mathematical and a numerical model. The effects of elastic deformation on body motion has been taken in account. In this way the phenomenon of in plane motion vibration of blade has been highlighted, and the amplification between amplitude speed oscillation of encoder disk and amplitude of blade speed oscillation has been evaluated by numerical model (21.4 dB) and compared with the measurement results (20±1 dB).