In complex systems like aircraft engines and oil refinery machines, pipeline inspection is an essential task for ensuring safety. Here, we proposed a type of smart material–driven pipeline inspection robot (weight, 2.2 grams; length, 47 millimeters; diameter, <10 millimeters) that could fit into pipes with sub-centimeter diameters and different curvatures. We adopted high–power density, long-life dielectric elastomer actuators as artificial muscles and smart composite microstructure–based, high-efficiency anchoring units as transmissions. Fast assembling of components using magnets with an adjustable number of units was used to fit varying pipeline geometries. We analyzed the dynamic characteristics of the robots by considering soft material’s unique properties like viscoelasticity and dynamic vibrations and tuned the activation voltage’s frequency and phase accordingly. Powered by tethered cables from outside the pipe, our peristaltic pipeline robot achieved rapid motions horizontally and vertically (horizontal: 1.19 body lengths per second, vertical: 1.08 body lengths per second) in a subcentimeter-sized pipe (diameter, 9.8 millimeters). Besides, it was capable of moving in pipes with varying geometries (diameter-changing pipe, L-shaped pipe, S-shaped pipe, or spiral-shaped pipe), filled media (air or oil), and materials (glass, metal, or carbon fiber). To demonstrate its capability for pipeline inspection, we installed a miniature camera on its front and controlled the robot manually from outside. The robot successfully finished an inspection task at different speeds.

Dielectric elastomer actuators (DEAs) as a typical class of electroactive polymers have been developed rapidly in the last two decades due to their advantages such as large strain, high energy density, and fast response. The high‐frequency characteristics of DEAs enable them to be applied in a wider range of fields. In this review, the high‐frequency (>10 Hz) characteristics and applications of DEAs are focused on. The basic concepts and metrics for high‐frequency DEAs are first given. Next, the commercial and synthesized dielectric and electrode materials of DEAs used in high‐frequency applications are reviewed. Following materials, strategies for extending the lifetime of DEAs are introduced. Subsequently, the dynamic modeling approaches for DEAs are presented, considering damping, inertia, and the electrical loss. Building on the fundamental research, some important applications are summarized based on the high‐frequency motions of DEAs including loudspeakers, active vibration suppression, pumps/valves, haptic devices, and high‐speed mobile robots. Finally, the conclusions and future perspectives are given. This review will give readers a clearer understanding of how to design and use high‐frequency DEAs.

Singularity analysis is one of the most important issues in the field of parallel manipulators. An approach for singularity analysis should be able to not only identify all possible singularities but also explain their physical meanings. Since a parallel manipulator is always out of control at a singularity and its neighborhood, it should work far from singular configurations. However, how to measure the closeness between a pose and a singular configuration is still a challenging problem. This paper presents a new approach for singularity analysis of parallel manipulators by taking into account motion/force transmissibility. Several performance indices are introduced to measure the closeness to singularities. By using these indices, a uniform “metric” can be found to represent the closeness to singularities for different types of nonredundant parallel manipulators.

Recently, various soft universal grippers have been developed due to their reduced control complexity and satisfying grasping capability. The gripping range of a gripper plays a key role in its universality. This article presents a pneumatically actuated soft-rigid hybrid multifinger gripper that has a wide gripping range by adjusting its initial grasp postures. The gripper is compact (dimensions: $\text{100} \times \text{60} \times \text{170}$ mm), lightweight (weight: 380 g), and modular. It consists of four modules, with each module containing three pneumatic actuators (a distance-adjusting actuator, an angle-adjusting actuator, and a finger actuator) and rigid connectors. Through initial grasp posture adjustment, and fingers with tapered angles to generate nonconstant bending while grasping, the gripper can grasp objects of a wide variety of sizes and weights, thus increasing its universality. The gripper is tested to characterize its distance adjustment range, angle adjustment range, and stiffnesses in load-bearing directions, at continuously changing pneumatic pressures. The distance adjustment range and angle adjustment range of the gripper are 0–64.4 mm (64.4% of the initial gripper length) and 0 $^{\circ}$ –140 $^{\circ}$ , respectively. The maximum stiffnesses of distance-adjusting actuator and angle-adjusting actuator are 3331 and 1.15 N $\cdot$ m/rad, respectively. Finally, grasping experiments show that our gripper can successfully grasp objects with diameters ranging from 0.5 to 180 mm, lengths ranging from 10 to 325 mm, and the heaviest object it can grasp is 2.1 kg (more than five folds of its own weight). The results demonstrated that our pneumatic gripper has an increased gripping range without adding other types of energy sources and its enhanced universality will expedite various applications in daily life and industry.

The spherical 5R parallel manipulator is a typical parallel manipulator. It can be used as a pointing device or as a minimally invasive surgical robot. This study addresses the motion/force transmission analysis and optimization of the manipulator by taking into account the motion/force transmissibility. The kinematics of the manipulator is analyzed. Several transmission indices are defined by using screw theory for the performance evaluation and dimensional synthesis. The process of determining the optimal angular parameters based on performance charts is presented. The manipulator that has a large workspace and good motion/force transmissibility is identified.

Because of the increasing demand in industry for A/B-axis tool heads, particularly in thin wall machining applications for structural aluminium aerospace components, the three-degree-of-freedom articulated tool head with parallel kinematics has become very popular. This paper addresses the dimensional optimization of two types of tool head with $3-P̱VPHS$ and $3-P̱VRS$ parallel kinematics (P, R, and S standing for prismatic, revolute, and spherical joint, respectively; the subscripts V and H indicating that the direction of the P joint is vertical or horizontal, and the joint symbol with underline means the joint is active) by considering their orientation capability and positioning accuracy. We first investigate the tilt angle of the spherical joint, the orientation capability, and the error of one point from the mobile platform caused by input errors. Optimization of the $3-P̱VPHS$ tool head is easy. For the $3-P̱VRS$ tool head, a design space is developed to illustrate how the orientation capability and error index are related to the link lengths. An optimization process is accordingly presented. Using the optimization method introduced here, it is not difficult to find all the possible optimal solutions.