Design and Dynamic Control: A Free-Flying Space Robot Inspired by Water Striders.

This work designed a free-flying space robot (FFSR) that simulates the on-orbit assembly of large space telescopes, drawing inspiration from the flexible movement of water striders on water surfaces. Initially, we developed the system structure of the robot, including the corresponding air-floating ground simulation system. This system enables floating movement of the robot in a gravity-free environment through the utilization of planar air bearings. Subsequently, we established the kinematics and dynamics models for the FFSR. Following that, we propose a novel adaptive boundary layer fuzzy sliding mode control (ABLFSMC) method to achieve trajectory tracking control of the FFSR. The virtual angle and angular velocity are formulated to serve as references for the angle and angular velocity in the body coordinate system. Furthermore, a fuzzy logic system is employed to minimize the chattering effect of the sliding mode control. The global stability of the proposed controller is guaranteed through the Lyapunov stability theory. Finally, we validate the effectiveness of the proposed control method as well as the high trajectory tracking accuracy of the developed FFSR through simulation and experimental results, respectively. Overall, our findings present a crucial experimental platform and development opportunity for the ground-based validation of technologies concerning the on-orbit assembly of large space telescopes.

Lightweight Force-Controlled Device for Freehand Ultrasound Acquisition.

This study investigates a force-controlled auxiliary device for freehand ultrasound (US) examinations. The designed device allows sonographers to maintain a steady target pressure on the US probe, thereby improving the US image quality and reproducibility. The use of a screw motor to power the device and a Raspberry Pi as the system controller results in a lightweight and portable device, while a screen enhances user-interactivity. Using gravity compensation, error compensation, an adaptive proportional-integral-derivative algorithm, and low-pass signal filtering, the designed device provides highly accurate force control. Several experiments using the developed device, including clinical trials relating to the jugular and superficial femoral veins, validate its utility in ensuring the desired pressure in response to varying environments and prolonged US examinations, enabling low or high pressures to be maintained and lowering the threshold of clinical experience. Moreover, the experimental results show that the designed device effectively relieves the stress on the sonographer's hand joints during US examinations and enables rapid assessment of the tissue elasticity characteristics. With automatic pressure tracking between probe and patient, the proposed device offers potentially significant benefits for the reproducibility and stability of US images and the health of sonographers.

Portable Device to Assist With Force Control in Ultrasound Acquisition.

This study presents a portable device that ensures precise contact force between a subject and a probe to improve the stability and reproducibility of ultrasound (US) acquisition. The mechanical portion of the device includes a servo motor, gears, and a ball screw linear actuator; two photoelectric switches are used to limit the stroke. A combined force and position control system is developed, and a pressure threshold is introduced to reduce the chattering of the system so that it can be applied to US examinations of tissues of different stiffness levels. Force control experiments were conducted on the device, and the results showed that the device can overcome the chattering of a physician's hand and movement caused by a subject's respiration. Additionally, the stability of the US acquisition was substantially improved. Based on clinical trials on humans, this device was observed to improve the consistency of ultrasonic results and the repeatability of images, and it assisted sonographers with maintaining suitable contact force and improving imaging quality. The device can either be handheld by a physician or easily integrated with a manipulator as an autonomous robotic US acquisition device, thereby validating its potential for US applications.

Adaptive nonsingular fixed-time sliding mode control for uncertain robotic manipulators under actuator saturation.

This paper describes an adaptive nonsingular fixed-time sliding mode control (ANFSMC) scheme under actuator saturation that can track the trajectory of a robotic manipulator under external disturbances and inertia uncertainties. First, a novel NFSMC that offers rapid convergence and avoids singularities is proposed for ensuring robotic manipulators global approximate fixed-time convergence. An ANFSMC is then developed for which the bound of the coupling uncertainty is not necessary to know in advance. The controller exhibits small absolute tracking errors and consumes little energy. An actuator saturation compensator is designed and shown to minimize the chattering of the system while accelerating the trajectory tracking. The proposed schemes are analyzed using Lyapunov stability theory, and their effectiveness and superiority are demonstrated through numerical simulations.