Sensors and Actuation Technologies in Exoskeletons: A Review

Exoskeletons are robots that closely interact with humans and that are increasingly used for different purposes, such as rehabilitation, assistance in the activities of daily living (ADLs), performance augmentation or as haptic devices. In the last few decades, the research activity on these robots has grown exponentially, and sensors and actuation technologies are two fundamental research themes for their development. In this review, an in-depth study of the works related to exoskeletons and specifically to these two main aspects is carried out. A preliminary phase investigates the temporal distribution of scientific publications to capture the interest in studying and developing novel ideas, methods or solutions for exoskeleton design, actuation and sensors. The distribution of the works is also analyzed with respect to the device purpose, body part to which the device is dedicated, operation mode and design methods. Subsequently, actuation and sensing solutions for the exoskeletons described by the studies in literature are analyzed in detail, highlighting the main trends in their development and spread. The results are presented with a schematic approach, and cross analyses among taxonomies are also proposed to emphasize emerging peculiarities.

DC Bus Voltage Control of Grid-Side Converter in Permanent Magnet Synchronous Generator Based on Improved Second-Order Linear Active Disturbance Rejection Control

In the permanent magnet synchronous generator (PMSG), the DC bus voltage fluctuates up and down under the influence of the load and power grid, which greatly affects the safe and reliable work of PMSG. In order to suppress the wide range fluctuation of DC bus voltage under disturbance and enhance its anti-disturbance performance, an optimized DC bus voltage control strategy is proposed by using the improved linear active disturbance rejection control (LADRC) in the voltage outer loop. By considering factors, such as load disturbance and grid voltage mutation as the total disturbance of the system, the improved reduced-order linear expansion state observer (RLSEO) is used to estimate and compensate the total disturbance, which greatly improves the stability of DC bus voltage. Firstly, the mathematical model of grid-side converter is established. On this basis, the LADRC control based on RLESO is designed, which reduces the phase lag of the linear extended state observer (LESO) and enhances the disturbance observation accuracy of the system. Then, a lead lag correction link is added to the total disturbance channel of RLESO to reduce the noise amplification effect of RLESO. Finally, the frequency domain characteristic analysis and stability proof of the improved LADRC control strategy are carried out. The simulation results show that the control strategy proposed in the article has a better control effect on the DC bus voltage.