Adaptive grasping is an important approach for robotic grippers to handle objects with irregular shapes. Compared to rigid-link-based adaptive grippers, the continuum-structure grippers benefit from their structural compliance and have thus a higher degree of adaptive grasping freedom. Based on this advantage, we have developed a continuum-structure-based double-finger gripper in this article to achieve the adaptive grasping. To improve the design efficiency, a 3-D-topology-optimization-based design method was adopted in this article, which realized the adaptive-grasping function of the robotic finger by introducing an additional spring into the design problem. The proposed robotic gripper was selective-laser-sintered with the material polyamide (PA2200) and was actuated by a linear motor. Experiments were also conducted to evaluate the grasping performance and load capacity of the developed gripper. Results have shown that the gripper could successfully grasp objects of different shapes and materials. In addition, with a total weight of only 180 g, the developed gripper can achieve a maximum grasping payload of 8.8 kg, which is about 49 times of its self-weight. From the methodological point of view, this work has successfully demonstrated the feasibility of optimization-based automatic design of robotic grippers.

Robotic legs are an important component of the quadruped robot for achieving different motion gaits. Although the conventional rigid-link-based legs can generally perform robust motions, they still have the issues with poor sealing when operating in complex and liquid terrains. To cope with this problem, fully compliant legs with monolithic structure have been introduced in recent years to improve the system compactness and structural compliance of quadruped robots. In this article, we present a topology-optimization-based method to achieve efficient design of compliant robotic legs. In order to balance the structural stiffness and bending flexibility of the realized leg, a multi-objective optimization algorithm is utilized. A series of design cases are presented to illustrate the design principle and analytical procedure of the proposed method. In addition, experimental evaluation is also performed, and the results have demonstrated that, a quadruped robot with the optimized legs can successfully achieve stable and continuous straight-line walking motions.

Compliant mechanisms are widely used in the design of medical robotics and devices because of their monolithic structure and high flexibility. Many compliant mechanisms derive their design ideas from nature, since the structure of biological organisms sometimes offers a better solution than the conventional mechanisms. However, the bio-inspired structures usually have very complex geometries which cannot be easily modeled and analyzed using traditional methods. In this paper, we present a novel finite element method (FEM) based modeling framework in Matlab to analyze the mechanics of different bio-inspired compliant mechanisms. Since the basic linear FEM formulation can only be employed to model small displacements of compliant mechanisms, a non-linear FEM formulation that integrates the modeling of large displacements, tendon-driven mechanisms and contact problems was implemented in the proposed framework to overcome the limitations. Simulations and experiments were also conducted to evaluate the performance of the modeling framework. Results have demonstrated the accuracy and plausibility of the proposed non-linear FEM formulation. Furthermore, the proposed framework can also be used to achieve structural optimization of bio-inspired compliant mechanisms.

Flexure-joint-based continuum robots are used in a variety of engineering applications, such as minimally invasive surgery and space exploration. However, some highly flexible joints, such as the leaf-spring joint, have a low torsional stiffness, which greatly limits the payload capacity of the constructed continuum robots in their curved configuration. On the other hand, some high-torsional-stiffness joints, such as the cartwheel joint, also suffer from the issue of stress concentration. To cope with these problems, in this article, we propose a 3-D-topology-optimization-based method in this article to achieve multiaxis design of flexure joints. Using a multiobjective algorithm, the torsional stiffness and rotational flexibility of different axes of the joint structure are taken into account in the optimization process. In addition, artificial spring elements are introduced in the design problem to realize a balanced stress distribution. To evaluate the feasibility of the proposed method, experiments are also performed to test the bending performance and torsional stiffness of the constructed continuum robot. Results have demonstrated that, the continuum robot equipped with the optimized flexure joints can successfully achieve high torsional stiffness while maintaining its bending flexibility.

Tendon-driven continuum robots are widely used in different engineering disciplines due to their simple structure and high flexibility. The typical structure of a tendon-driven continuum robot usually contains a series of identical compliant joints in its backbone to achieve large-deflection bending movements. However, with compliant joints of the same geometry, the real bending shape of the robot backbone is an arc with variable curvature, which results in uneven stress distribution along the robot backbone. In the long term, higher stresses in the compliant joints near the fixation base could lead to fatigue or fracture of the entire robot structure. To cope with this problem, we propose a fish-tail-inspired method in this letter to optimize the stress distribution along the serial compliant joints. Several optimization examples were presented to show the performance of the proposed method. Simulation and experimental results have demonstrated that the developed method can effectively reduce the stress differences in serial compliant joints during large-deflection bending movements.

In this paper, we present a novel method for achieving automatic design of compliant surgical forceps with adaptive grasping functions. Compliant forceps are much easier to assemble and sterilize than conventional rigid-joint forceps, hence their use is spreading from traditional open surgery to robot-assisted minimally invasive applications. However, many compliant forceps still perform stiff grasping, and thus can damage sensitive organs and tissues during the operation. Adaptive grasping function is therefore required for safe manipulation of vulnerable structures. Currently, it is difficult and time consuming to use empirical methods for designing adaptive compliant forceps for different surgical robotic applications. To cope with this problem, we developed a topology-optimization-based method able to synthesize adaptive compliant forceps automatically. Simulation and experimental tests were conducted to evaluate the adaptive grasping function of designed surgical forceps. The results demonstrated that the developed method greatly simplifies the design process and makes it possible to efficiently realize task-specific compliant forceps.