Visit iXblue at

SPIE Optical Metrology


Visit iXblue at SPIE Optical Metrology



Tuesday 25 June 2019 4:10 PM - 4:30 PM

Session 6: Interferometry II

An improved control structure for the tracking of sine command in a motion simulator

Speakers: Mehdi Bussutil, Damien Ponceau, Bernard Vau – iXblue Motion Systems Division


The evaluation of inertial sensor’s frequency response is a crucial step during the development of such sensor (gyroscope, accelerometer…) or of that of the inertial navigation system.

An accurate measurement of the sensor’s gain and phase requires a test equipment, usually a motion simulator, able to create accurately controlled motions over a wide frequency band, with minimum amplitude and phase uncertainty. State-of-the-art motion simulators use brushless electric motors as actuators and optical encoders as angular position sensor. They also include a servo-loop (often made of PID controller) whose bandwidth is necessarily limited either for theoretical reasons, like the Bode Integral Theorem, or for physical ones, such as the inevitable time-lags occurring in the loop, or even mechanical resonances. Nevertheless, the appropriate bandwidth is required to allow for an accurate inertial sensor characterization. A well-known manner to cope with the intrinsic limitations of the feedback control structure in a servo-drive consists in introducing a specific filter (called feedforward) between the motion trajectory generator and the feedback loop, to provide an anticipation independently of the feedback structure.

This compensation requires a good modelling of the controlled system transfer function but is never perfect. Moreover, in a motion simulator, the tested inertial equipment is subject to change, and a unique feedforward filter cannot provide an accurate enough compensation. Thus, iXblue has introduced an adaptive feedforward structure in the controllers of their motion simulators, leading to a more accurate tracking of sine commands, beyond the initial closed-loop bandwidth.

The benefits of this control structure reveal to be very significant: a very accurate sine tracking is obtained, with very small amplitude attenuation and phase lag.