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

A novel design concept for buckling-induced mechanical metamaterials for energy dissipation is presented. A topology optimization formulation is proposed, where the force-displacement curves of the unit cells of the metamaterials are tailored to maximize the buckling-induced dissipated energy in a mass constraint. A two-phase algorithm is proposed to find the optimized result from a uniform initial guess. The optimized design has a larger amount of buckling-induced dissipated energy than the structural prototypes based on the designers' intuition.

Topology Optimization of Metamaterials for Energy Dissipation

Design and Optimization of a Decoupled Rp Flexure Joint for an Adjustable-Motion-Direction Compliant Mechanism

Topology optimized compliant mechanisms have been widely utilized as the microdevices in microelectromechanical system. In applying topology optimization to design compliant mechanisms, one of the longstanding problems is that the obtained mechanisms often have highly localized compliance regions which make them very difficult to fabricate. In order to obtain manufacturable topology optimized compliant mechanisms, this paper presents a robust formulation based on the level set method. In the formulation, the goal is to maximize the objective for the worst case of three different structural configurations which are represented by three different level set functions. Not only the formulation can eliminate the highly localized compliance regions, it also can precisely control the minimum length scale in the obtained mechanisms. The validity and different aspects of the proposed formulation are demonstrated on several benchmark problems.

Topological Synthesis of Compliant Mechanisms Using a Level Set-Based Robust Formulation

A multistable compliant mechanism and a stability state analysis method thereof. The multistable compliant mechanism is formed by sequentially connecting a plurality of basic units (101) end to end, so as to form a closed annular structure (1). Each basic unit (101) comprises two flexible hinge portions (102, 103) perpendicular to each other on different planes, and two rigid connecting portions (104, 105) for connecting the flexible hinge portions (102, 103). The two flexible hinge portions (102, 103) are connected via one of the rigid connecting portions (104) disposed therebetween, and one of the flexible hinge portions (103) is connected to a flexible hinge portion (102) of an adjacent basic unit (101) via the other rigid connecting portion (105). The lengths of two rigid connecting portions (104, 105) in the same basic unit (101) must be equal, but the lengths of rigid connecting portions (104, 105) in different basic units are not necessarily equal.

Multistable compliant mechanism and stability state analysis method thereof


 This paper presents a modified evolutionary topology optimization method for designing compliant constant force mechanismS (CFMs). CFM is defined as mechanism that can generate constant force in the desired input displacement range, which is known as constant force range. The force variation, i.e. fluctuation of output forces over the constant force range, is a critical parameter, which reflects the stability of the output force. The key idea of the new method is that the design variables are increased or decreased for a certain small value instead of being changed between 0 (or x_{min} ) and 1 in other evolutionary structural optimization (ESO) method. As the CFMs have to experience a large deformation when it works, the influence of the nonlinearity need to be considered. An additive hyperelasticity technique is utilized to alleviate the instability of the finite element analysis, which is introduced by the low stiffness elements. The numerical examples show that the proposed design method can generate CFMs with desired constant force range and aspect ratio. The optimized CFM is manufactured by the 3D printing and the experimental result indicates that it can output an almost constant force(force variation ≤=2%) in a large relative constant force range(56.7%).

Hongchuan Zhang

Papers

Topology Optimization of Metamaterials for Energy Dissipation

Design and Optimization of a Decoupled Rp Flexure Joint for an Adjustable-Motion-Direction Compliant Mechanism

Topological Synthesis of Compliant Mechanisms Using a Level Set-Based Robust Formulation

Multistable compliant mechanism and stability state analysis method thereof

Topology Optimization Method for Designing Compliant Mechanism with Given Constant Force Range