Design of compliant mechanisms using continuum topology optimization: A review

Lattice structures, which are also known as architected cellular structures, have been applied in various industrial sectors, owing to their fascinated performances, such as low elastic modulus, high stiffness-to-weight ratio, low thermal expansion coefficient, and large specific surface area. The lattice structures fabricated by conventional manufacturing technologies always involve complicated process control, additional assembly steps, or other uncontrollable factors. Furthermore, limited types of unit cells can be used to construct lattice structures when using conventional processes. Fortunately, additive manufacturing technology, based on a layer-by-layer process from computer-aided design models, demonstrates the unique capability and flexibility and provides an ideal platform in manufacturing complex components like lattice structures, resulting in an effective reduction in the processing time to actual application and minimum of material waste. Therefore, additive manufacturing relieves the constraint of structure design and provides accurate fabrication for lattice structures with good quality. This work systematically presents an overview of conventional manufacturing methods and novel additive manufacturing technologies for metallic lattice structures. Afterward, the design, optimization, a variety of properties, and applications of metallic lattice structures produced by additive manufacturing are elaborated. By summarizing state-of-the-art progress of the additively manufactured metallic lattice structures, limitations and future perspectives are also discussed.

Additive manufacturing of metallic lattice structures: Unconstrained design, accurate fabrication, fascinated performances, and challenges

Vibration control based metamaterials and origami structures: A state-of-the-art review

Improving the functionality of soft continuum manipulators to expand their application space has always been an important development direction for soft robotics. It remains very challenging to calculate the deformations of soft materials and predict the basic structure of soft fingers under complex objective functions and constraints. This work develops a cable-driven soft robotic gripper with multi-input and multi-output using topology optimization considering geometric nonlinearity, which not only performs adaptive grasping but also enables finer manipulations such as rotating or panning the target. A scheme that can describe adaptive grasping behavior is proposed, which converts the contact between the clamping surface and the object into a boundary condition to circumvent complex contact nonlinearities. An additive hyperelasticity technique is used to overcome numerical instabilities, and the finite element analysis is performed in ANSYS. Numerical simulations and experimental results are performed to demonstrate the effectiveness of the optimization algorithm and to illustrate the application potential of the proposed gripper.

Topology optimization of a cable-driven soft robotic gripper

The piezoelectric-actuated compliant microgripper (PEACM) plays an essential role in the application fields such as biomedical engineering, microelectronics, and optical engineering. As compared with other categories of grippers, PEACM exhibits the advantages of high accuracy of displacement, large power to weight ratio, low energy consumption, and fast response speed. This paper reviews the recent advances on performance indices, classification, structural composition, optimization and modeling method, and control of PEACM. First, the gripper's performance indices and classifications are elaborated, which is beneficial to determine the design goal. Then, the compliant mechanisms adopted in the microgripper design are discussed, including the flexible hinge, displacement amplifier, and guiding mechanism. In addition, the optimization and modeling methods of the microgripper are presented. Popular types of position/force sensors and different displacement/force control strategies employed in the microgripper are surveyed. Moreover, the prospect on future development trend of the PEACM is discussed. The paper provides the reader with an overview of the recent advances on PEACM design and also a guideline on further development of the microgripper.

Recent design and development of piezoelectric-actuated compliant microgrippers: A review

In this article, a novel force sensor is designed based on the optical fiber bending loss theory utilizing a structure with periodically corrugated semicircular flexure beam units. The fiber bending loss theory composed of the pure bending loss and the transition loss is related to the curvature radius according to the theoretical analysis. Both the optical working modes and the mechanical properties of the designed sensor are discussed. The output voltage attenuation of different curvature radii is tested and the curvature radius of 6 mm is selected for further experiment. The actual sensing results are acquired using a commercial force sensor. The result shows that the nonlinear errors of the forward and the reverse force applying process are 11.82% and 17.86%, respectively. The sensitivity is 13 mV/N and the precision is 160 mN. The experiment under different temperatures ensures the temperature-insensitive characteristics of the sensor.

A Novel Force Sensor Based on Optical Fibers Used for Semicircular Flexure Beam Unit


 The symmetrical origami Waterbomb(WB) base shows promising applications in engineering due to its considerable mechanical behaviors. As the common phenomenon in actual origami, the stability performance of the WB base has attracted more and more attention. However, there are few studies on graphical design for the stability of WB base. Based on the phase diagram of the intrinsic parameters, this paper proposes an intuitive and synthesized stability design method for the WB base. First, the basic principles are demonstrated by using the Euler-Lagrange functional equation. Besides, the detail of the method is illustrated by two typical WB bases with the given stiffness ratio. Second, according to the proposed design method, the case studies are presented, and the stability behaviors are evaluated by the analytical method and Finite Element Analysis(FEA) simulation. Finally, the prototypes of the case study are designed, the measurement experiment of the stable statuses is carried out. Both FEA simulation and the experimental result can demonstrate the effectiveness of the proposed design method.

A Phase Diagram-Based Stability Design Method for a Symmetrical Origami Waterbomb Base

A novel one-degree-of-freedom translational partly compliant mechanism with variable motion direction

This paper presents a compliant mechanisms synthesis method using moving morphable components (MMC) topology optimization with a view of replacing de facto hinges by specific flexure hinge characteristic. The shape of a common used corner-filleted hinge is embed into the profile of quadratically varying thickness component. The geometric parameters of the hinge is treated as design variables, participate in the optimization process directly. To obtain relatively stable topological configurations in different spring stiffness, keynodes connectivity preservation is applied which can provide a forced connection between components and input, output and fixed ports. The validity of the method is demonstrated using numerical examples.

Topology Optimization of Compliant Mechanisms Using Moving Morphable Components with Flexure Hinge Characteristic


 This paper presents a novel wheel-legged mobile robot with a reconfigurable frame, which uses a compliant kaleidocycles inspired spring-hinged eight-bar mechanism. The kinematic model of the mechanism is established and the relationships between actual rotation angle and the joint angles is thoroughly obtained in the spherical coordinate system. According to the analysis of the multivariable potential energy surface, the relationship among multistable performance, under-actuated behavior and potential mechanism energy is studied. On account of under-actuated kinematic relationship and multistability of the proposed mechanism, a cable-driven approach is used and its feasibility is finally verified by the experiment of the prototype robot.

Hongchuan Zhang

Papers

A Novel Force Sensor Based on Optical Fibers Used for Semicircular Flexure Beam Unit

A Phase Diagram-Based Stability Design Method for a Symmetrical Origami Waterbomb Base

A novel one-degree-of-freedom translational partly compliant mechanism with variable motion direction

Topology Optimization of Compliant Mechanisms Using Moving Morphable Components with Flexure Hinge Characteristic

A Novel Reconfigurable Wheel-Legged Mobile Mechanism