This article presents a frog-inspired swimming soft robot whose joints are articulated pneumatic soft actuators. The soft actuator is designed and prepared by studying the biological structure and limb movement characteristics of frogs. A schematic limb motion diagram of the robot is established based on the kinematic model, and the design scheme is determined by a combined control system. The torso size is 0.175 × 0.100 × 0.060 m, which realizes frog-inspired swimming robot miniaturization. The experimental results show that the average propulsion speed during linear motion is 0.075 m/s, and the average turning speed is 15°/s. The rationality of the robot structural design and correctness of the control system are verified by prototype experiments.

This article presents the design, fabrication, modeling, and preliminary tests of a bloodworm-inspired soft gripper for universal grasping. The gripper was designed and fabricated based on a toy called water snake wiggly (WSW). The toroidal WSW can evert itself inside-out or outside-in, just like a bloodworm everting its teeth outside to hunt and inside to feed. By driving a WSW rolling itself outside-in to wrap around the items, a bloodworm-inspired gripper was achieved with a flexible and passive form-fitting grasp. To enhance the capability of the gripper, two alternative detachable modules were added to the gripper—a vacuum suction cup for handling objects with smooth nonporous surfaces and an end-needle for taking in and expelling noncorrosive liquids like a syringe. We analyzed the working principles of the gripper and derived the relationship between the gripper's holding force and the objects' scale. Preliminary experiments with a motor-driven gripper prototype were conducted to verify its performance. The experimental results conform well with our theoretical analysis and also indicate the gripper's good universal grasping capacity and reliability in handling a wide range of objects with different surface shapes, geometric dimensions, and stiffness. In addition, the gripper has the unique abilities to pick more than one object during a maneuver, grasp multiple objects in a row without releasing the former ones, and even grasp powdered objects. These have presented a challenge for the existing robotic grippers.

This paper focuses on the problem of extracting the physical dynamic parameters which are fundamental for computing the positive-definite link mass matrix. To solve this problem, a minimal set of dynamic parameters were firstly identified by the standard least squares method. In order to simplify the dynamics model, a new set of essential dynamic parameters were calculated by eliminating the poorly identified parameters with an iterative approach. Based on these dynamic parameters with better identification quality, a universally global optimization framework was proposed here to retrieve the set of physical dynamic parameters of a serial robot, in which parameter bounds, linear and nonlinear constraints with physical consistency can be easily considered, such as the triangle inequality of the link inertia tensors, the total link mass limitations, other user-defined constraints and so on. Finally, validation experiments were conducted on the KUKA LBR iiwa 14 R820 robot. The results show that the proposed optimization framework is effective, and the identified dynamic parameters can predict the robot joint torques accurately for the validation trajectories.

Improving the comfort and portability of exoskeleton structures for human locomotion assistance is challenging. Research shows that the misalignments between exoskeletons and human joints will lead to interference and undesired interaction forces in locomotion. Moreover, the weight and inertia of exoskeletons will lead to rapid changes in impact forces acting on the wearer. When the exoskeleton is tightly bound to the wearer’s body, such forces are usually unavoidable. These issues not only reduce the comfort and portability of exoskeletons, but also increase the energy costs to wearers. To address these issues, we propose a novel lower limb exoskeleton with a constant-force suspension mechanism and self-adapting compliant joints. The constant-force suspension mechanism aims to isolate the impact force on the back of the wearer, while the self-adapting compliant joints aim to reduce the misalignments between the exoskeleton and the wearer. For the first time, a structure designed to isolate the impact force of exoskeletons is proposed. Moreover, compliant joints exhibiting comprehensive great performances in portability, flexibility, self-aligning, and weight-supporting ability have also been rarely reported. The experimental results demonstrate that the developed mechanisms can reduce the impact forces and misalignments in locomotion. Furthermore, the proposed exoskeleton can reduce the metabolic rate during walking at 5 km/h by 10.95 $\pm$ 4.40% and that during running at 9 km/h by 1.71 $\pm$ 4.54% compared with locomotion without the exoskeleton. These results confirm that the proposed designs can improve the performance of the exoskeleton in locomotion.

This paper presents an adaptive decoupling control strategy for a gyroscopically stabilized pendulum. In the proposed model, the gyro moment acts directly on the pivot of the pendulum, the magnitude of which is restricted by gyroscopic precession. A decoupling algorithm based on virtual control is proposed to regulate the upright posture of the pendulum through gyroscopic precession. Virtual control is considered a control torque that acts on the pivot of the pendulum; it forms nonlinear mapping along with the precession command. Consequently, gyroscopic precession matches the stability condition of the pendulum well. In the control design, an adaptive disturbance estimation method based on a smooth saturation function is proposed to avoid the adverse effects of parametric uncertainties, mechanical vibrations, and system nonlinearities. Accurate estimation of unstructured disturbances is easily achieved by adaptively tuning the weight coefficient of the saturation function. The results of stability analysis, simulations, and experiments show the validity of the proposed pendulum model and adaptive decoupling control scheme.