The advancement in technology has seen a rapid increase in the use of unmanned aerial vehicles for various applications. These unmanned aerial vehicles are often equipped with the imaging platform like a camera. During the unmanned aerial vehicle flight, the camera is subjected to vibrations which hamper the quality of the captured images/videos. The high-frequency vibrations from the unmanned aerial vehicle are transmitted to the camera. Conventionally, passive rubber mounts are used to isolate the camera from the drone vibrations. The passive mounts are able to provide reduction in response near the resonance. However, this comes at the cost of amplification of response at the higher frequency. This article proposes an active vibration isolation system which exhibits improved performance at the higher frequencies than the conventional system. The active isolation system consists of a contact-less voice coil actuator supported by four springs. Experiments are carried out to study the effect of vibrations on the quality of images captured. The characterization of drone vibrations is also carried out by recording the acceleration during different flight modes. The performance of the proposed isolation system is experimentally validated on a real drone camera subjected to the recorded drone acceleration spectrum. The isolation system is found to perform better than the conventional rubber mounts and is able to reduce the vibrations to a factor of one-fourth. It can be effectively used to improve the image acquisition quality of the unmanned aerial vehicles.

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.

Collocated control has the advantages of robustness and guaranteed stability. In collocated control, the sensor and actuator are placed close to each other. True collocation can be achieved using self-sensing in which the actuator can also be used as a sensor. In this article, we present a self-sensing electromagnetic actuator for vibration control of flexible structures. The back electromotive force (emf) generated in the coil is measured to evaluate the velocity of the structure (and hence, the displacement). The position measurements obtained from self-sensing are found to have good correlation with those obtained using an eddy current sensor. The efficacy of the proposed technique has been verified for the vibration control of a flexible cantilever beam. Self-sensing offers economical, simple and robust control architecture. It can be effectively used for applications where sensors and actuators cannot be collocated due to space and size limitations.

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Reaction wheels are widely used in the attitude control of spacecraft due to their capability of applying control torques, greatly reducing the propellant requirements and limiting its use to reaction wheel desaturation. However, the presence of unavoidable mechanical imperfections results in significant mechanical disturbances, being applied to the spacecraft, which can severely impact the operation of sensitive payloads. These microvibrations are broadband in nature, and therefore the effective mitigation of their effects requires a high isolation factor throughout a wide frequency range. This paper presents the development and experimental verification of a six-degree-of-freedom active isolation platform for a reaction wheel, integrating a soft suspension and active control using self-sensing actuators. A reduction in the transmitted forces of 65 dB at 270 Hz was experimentally demonstrated, while exhibiting negligible amplifications by its suspension resonance, which constitute very attractive performances.