The technological developments in the field of image based sensing have led to a vast growth in the use of drones in various domains. The drone is usually equipped with an image sensor (camera) which collect images over the target area. These images are then post-processed to extract the important information. Efficiency and accuracy of the image based sensing are largely dependent on the captured image quality. Therefore, it is important to prevent the transmission of the drone vibrations to the camera. Most of the current camera mounting systems use passive rubber mounts for isolation. However, these mounts are effective only in vertical direction and essentially adds damping to the system which degrades the performance of the isolation at high frequency. In this paper, a multi-degree of freedom isolation system, based on a Stewart platform configuration, is proposed for drone camera stabilization. The important features of the proposed isolation system are-(i) high frequency roll-off, (ii) no use of flexible joints, (iii) uses non-contact voice coil actuator thus avoiding spurious resonances of the legs, (iv) adjustable stiffness, (v) 3D printed lightweight parts and (vi) centralized control using a single sensor (inertial measurement unit). A prototype of the proposed system has been manufactured and validated experimentally. The proposed isolation system is found to reduce the response of the isolation system near resonance without compromising performance at high frequency. The application of the isolation system can be easily extended to other fields which require high quality image acquisition.

High performance control requires high loop gain and large control bandwidth. However, the spurious resonances at the higher frequencies can limit the performance of such type of systems. This drawback can be overcome by using sensor fusion technique. In sensor fusion, two or more sensors are combined in synergy such that good performance is achieved at lower frequencies while ensuring robustness of the system at higher frequencies. This paper presents a new technique, termed as ''virtual sensor fusion", in which only one of the sensors is physically installed on the system while the other sensor is simulated virtually. The virtual sensor is selected based on desired high frequency response. The effectiveness of the proposed technique is demonstrated numerically for a case of active seismic isolation. A robustness analysis of virtual sensor fusion is also carried out in order to study its stability in the presence of spurious resonances. Finally, the technique is experimentally verified on active isolation of pendulum system from ground motion. The results obtained demonstrate good isolation performance at lower frequencies and robustness to plant uncertainties (spurious resonances) at higher frequencies. This technique can be effectively used for high precision control of sensitive instruments.

This paper investigates the use of Integral Force Feedback (IFF) for the active damping of rotating mechanical systems. Guaranteed stability, typical benefit of IFF, is lost as soon as the system is rotating due to gyroscopic effects. To overcome this issue, two modifications of the classical IFF control scheme are proposed. The first consists of slightly modifying the control law while the second consists of adding springs in parallel with the force sensors. Conditions for stability and optimal parameters are derived. The results reveal that, despite their different implementations, both modified IFF control scheme have almost identical damping authority on suspension modes.

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