A Novel Generation Method of High Quality Video Image for High Resolution Airborne ViSAR

Video synthetic aperture radar (ViSAR) can provide long-time surveillance of a region of interest (ROI), which is one of the hotspot directions in the SAR field. In order to better display ViSAR, a high resolution and high frame rate are needed. Azimuth integration angle and sub-aperture overlapping ratio, which determine the image resolution and frame rate, respectively, are analyzed in depth in this paper. For SAR imaging algorithm, polar format algorithm (PFA) is applied, which not only has high efficiency but is also easier to integrate with autofocus algorithms. Due to sensitivity to motion error, it is very difficult to obtain satisfactory focus quality, especially for SAR systems with a high carrier frequency. The three-step motion compensation (MOCO) proposed in this paper, which combines GPS-based MOCO, map-drift (MD) and phase gradient autofocus (PGA), can effectively compensate for motion error, especially for short wavelengths. In ViSAR, problems such as jitter, non-uniform grey scale and low image signal noise ratio (SNR) between different aspects images also need to be considered, so a ViSAR generation method is proposed to solve the above problems. Finally, the results of ViSAR in THz and Ku band demonstrate the effectiveness and practicability of the proposed method.

MOTION CHARACTERIZATION OF A SWITCHED RELUCTANCE ACTUATOR – A SIGNAL DRIVEN APPROACH

In this paper, the researchers have described the development, design and characterization of a Switched Reluctance (SR) actuator, with a rotary motion, having a single-excitation activity. This SR actuator design consisted of a stator and rotor core and was based on the simplest SR actuator model design, with a Stator-to-Rotor pole ratio (S: R) of 6:4. In this design, the winding was coiled at Phase A, which enabled the single step motion characterization based on a single excitation. This SR actuator prototype showed a compact size, with a 36 mm stack length and a 60 mm outer diameter. This feature allowed small machine applications like the precision robotic machining, but required a low production cost, as it lacked a permanent magnet. On the other hand, the SR actuator consisted of highly non-linear characteristics and showed uncontrolled motion behavior. While achieving a very precise motion, it is important to suppress the non-linear characteristics of an actuator. Hence, the researchers designed the linearizer unit based on its characterization at Position 0°, which was related to the excitation current and the rotary angles for the various initial rotor positions. This initial position was chosen as it reflected the characteristics which indicated the self-starting characteristics. Thereafter, the researchers experimentally investigated the appropriate driving signal for this SR actuator as the normal step input signal showed a lower precision motion because of the discharging effect-related issues.

Variable step control to improve scanning speed of gene sequencing stage

High-speed scanning is a huge challenge to the motion control of step-scanning gene sequencing stage. The stage should achieve high-precision position stability with minimal settling time for each step. The existing step-scanning scheme usually bases on fixed-step motion control, which has limited means to reduce the time cost of approaching the desired position and keeping high-precision position stability. In this work, we focus on shortening the settling time of stepping motion and propose a novel variable step control method to increase the scanning speed of gene sequencing stage. Specifically, the variable step control stabilizes the stage at any position in a steady-state interval rather than the desired position on each step, so that reduces the settling time. The resulting step-length error is compensated in the next acceleration and deceleration process of stepping to avoid the accumulation of errors. We explicitly described the working process of the step-scanning gene sequencer and designed the PID control structure used in the variable step control for the gene sequencing stage. The simulation was performed to check the performance and stability of the variable step control. Under the conditions of the variable step control where the IMA6000 gene sequencer prototype was evaluated extensively. The experimental results show that the real gene sequencer can step 1.54 mm in 50 ms period, and maintain a high-precision stable state less than 30 nm standard deviation in the following 10 ms period. The proposed method performs well on the gene sequencing stage.

Somatosensory actuator based on stretchable conductive photothermally responsive hydrogel

Mimicking biological neuromuscular systems’ sensory motion requires the unification of sensing and actuation in a singular artificial muscle material, which must not only actuate but also sense their own motions. These functionalities would be of great value for soft robotics that seek to achieve multifunctionality and local sensing capabilities approaching natural organisms. Here, we report a soft somatosensitive actuating material using an electrically conductive and photothermally responsive hydrogel, which combines the functions of piezoresistive strain/pressure sensing and photo/thermal actuation into a single material. Synthesized through an unconventional ice-templated ultraviolet–cryo-polymerization technique, the homogenous tough conductive hydrogel exhibited a densified conducting network and highly porous microstructure, achieving a unique combination of ultrahigh conductivity (36.8 milisiemens per centimeter, 103-fold enhancement) and mechanical robustness, featuring high stretchability (170%), large volume shrinkage (49%), and 30-fold faster response than conventional hydrogels. With the unique compositional homogeneity of the monolithic material, our hydrogels overcame a limitation of conventional physically integrated sensory actuator systems with interface constraints and predefined functions. The two-in-one functional hydrogel demonstrated both exteroception to perceive the environment and proprioception to kinesthetically sense its deformations in real time, while actuating with near-infinite degrees of freedom. We have demonstrated a variety of light-driven locomotion including contraction, bending, shape recognition, object grasping, and transporting with simultaneous self-monitoring. When connected to a control circuit, the muscle-like material achieved closed-loop feedback controlled, reversible step motion. This material design can also be applied to liquid crystal elastomers.

Design, Mobility and Kinematics Analysis of a Novel Reconfigurable Continuum Shape Morphing Mechanism

This paper presents a novel design for morphing mechanisms that combine the passive lockable reconfigurable variable geometry truss manipulator (VGTM) and the active parallel compliant mechanism. The structure of the VGTM is in a parallel-serial structure and its shape can be fully controlled just by using two active panels. This mechanism is suitable for the aerospace application due to its light, compact structure, load-carrying ability and can achieve multiple degrees-of-freedom (DOFs) deformation. The mobility and topological configuration of the mechanism are thoroughly analyzed. To make the moving process simple and efficient, a control strategy combining the approximate motion mode and the precise motion modes was proposed. The kinematic models for the multi-step motion are established and all solved analytically. At last, a prototype was fabricated to show the structure and the application on morphing wings.