Search

Materials and structures with shape morphing capabilities are attractive in aerospace, maritime vehicles and robotics: such systems offer lighter weight, better distributed stresses, simpler kinematics, smaller numbers of actuators and higher reliability. Current morphing materials are either very compliant to achieve large shape changes (metamaterials, compliant mechanisms, hydrogels), or very stiff but with infinitesimal shape changes that require large actuation forces (metallic or composite sandwich panels with piezoelectric actuation). Morphing efficiency and structural stiffness are therefore mutually exclusive properties in current engineering morphing materials, which limit the range of their application. Here we propose a design for a stiff morphing beam made of "meta-elements" with unusual combinations of elastic properties, and which can be actuated from a simple push/pull at the base. To capture the performance of the beam we propose and use three metrics: The "morphing amplitude", the "morphing compliance" and "structural stiffness". We develop nonlinear finite elements to explore a wide range of designs, and to show some inevitable tradeoffs of stiffness and morphing. To aid the design of the structure we propose ternary diagrams to select optimum combinations of properties for the meta-elements. Finally, we fabricated and tested three prototypes of stiff morphing beams to validate the approach. [ABSTRACT FROM AUTHOR]

Notch flexure hinges with longitudinal/transverse asymmetries can be widely found in compliant mechanisms to balance the performance trade-offs. However, the transverse asymmetry often leads to difficult analyses of kinetostatics and dynamics. In this paper, a miniaturized piezoelectric gripper featuring reversed Scott-Russell compliant amplifier with transversely asymmetric single-notched flexure hinges is designed for use in confined spaces. The compliance and vibration characteristics of the transversely asymmetric single-notched flexure hinges are quantitatively analyzed by a new transfer matrix method. The proposed theoretical methodology involves discretizing the transversely asymmetric flexure hinge into a series of constant beam segments with non-coaxial nodes, which enables a straightforward modeling process and hence simplifies the kinetostatic and dynamic analyses of compliant mechanisms comprised of complex flexure hinges. Comparative validations with respect to the finite element simulation and experiments confirm the advantages of easy operation and small-scale equation sets of the proposed modeling method. As to the designed piezoelectric microgripper with single-notched flexure hinges, the jaw displacement amplification ratio of 20 and resonance frequency of 1250 Hz has been experimentally tested with a small size of 38 mm × 15 mm × 7 mm. [Display omitted] • A new transfer matrix of transversely-asymmetric flexure hinges is introduced. • A miniaturized reversed Scott-Russell amplified piezoelectric gripper is designed. • Kinetostatics and dynamics of the microgripper are formulated and analyzed. • A jaw stroke amplifying ratio 20 and resonance frequency 1250 Hz are achieved. [ABSTRACT FROM AUTHOR]

A stress-constrained topology optimization design for the multi-material thermo-hyperelastic compliant mechanism is investigated in this article, using inverse motion analysis. Through the inverse motion analysis approach, precise control over the geometry of the deformed structure is achieved. A topology optimization model is established for the multi-material thermal hyperelastic compliant mechanism, incorporating constraints on volume, cost and stress, while maximizing displacement as the objective function. Filtering is implemented using an improved partial differential equation, and the stress problem is addressed using the ϵ-relaxation method and the p-norm aggregation function. The sensitivity analysis of the displacement objective function and the stress constraint is conducted. Considering the multi-material thermally actuated actuator as an example, the influence of the stress constraint on the topology optimization design is studied. The results indicate that inverse motion analysis allows for effective control of the output end position of the deformed compliant mechanism. [ABSTRACT FROM AUTHOR]

An XY-compliant mechanism is a two-degree of freedom positioner which is considered to have some distinguishing characteristics in ultra-precision technology. To ensure a long working life, it is necessary to study the fatigue life, however, in the related works of the XY-compliant mechanism, no research into design optimization for maximum fatigue life has been conducted so far. Moreover, the sample size of fatigue data is often inadequate to develop a surrogate model. This paper pioneers a new method for maximizing the fatigue life of the proposed mechanism, in the context of small-size fatigue life samples. Particularly, the Synthetic Minority Oversampling Technique is utilized to enlarge the sample size. A machine learning technique is then applied to create the surrogate model, in which fatigue life is considered the output. The Hunger Games Search is then used to maximize the output. In this study, Steel A36 and AL 6061T6 materials are utilized for the mechanism. The numerical results of two case studies show that using Synthetic Minority Oversampling Technique can predict appropriately the fatigue life, compared to using the original data. Specifically, after taking the natural logarithm of fatigue life, the average mean square error when using simulated data is 1.8 % and 36.8 % better than when using original data, for Case 1 and Case 2, respectively. The optimal fatigue life found by the proposed method compared with the baseline is about 350 % for Case 1 and 1250 % for Case 2, respectively. The optimal findings are also confirmed using ANSYS software, in which the errors of fatigue life are less than 5 % . [ABSTRACT FROM AUTHOR]

Biological cells are exposed to a variety of mechanical stimuli from their environment. Cells convert these mechanical stimuli to specific biochemical signals through a process known as mechanotransduction, which is necessary for proper functioning of cells. Biaxial stretching is one such stimulus observed in tissues such as lung alveoli, pericardium, blood vessels and urinary bladder. To study the effect of biaxial stretching on cell function, or any other mechanotransduction process, it is essential to develop tools capable of manipulating cells in the respective deformation mode. Here, we report the design, fabrication and actuation of a compliant micromechanism for in-plane, biaxial stretching of single cells. Further, we demonstrate biaxial stretching of NIH-3T3 cells (mouse fibroblasts) using this micromechanism. Our device is an amalgam of a gripper mechanism and an auxetic structure, which can be actuated using a mechanical probe. Cells can be stretched equibiaxially or with any non-equibiaxial stretch ratio, by altering the mechanism geometry. The device is made of SU-8 using a two-layer lithography process. Since SU-8 is transparent and biocompatible, we could attach cells to the mechanism, stretch them and continuously image during stretching. Our device could be useful for elucidating the biological response of cells to biaxial stretching and for characterising the anisotropic mechanical properties of single cells. [ABSTRACT FROM AUTHOR]

Precision systems have extensively employed compliant mechanisms. Nevertheless, its utilization in vibration-assisted polishing has not garnered much interest. Therefore, this study presents a novel framework for a mechanism that adheres to two degrees of freedom. The mechanism that has been constructed exhibits a symmetrical design, enabling it to extract comparable performances in two directions. The proposed construction incorporates a novel combination of a three-lever amplification mechanism and a parallelogram to improve both the stroke and resonant frequency. The output amplification ratio is calculated by the graphical scheme method. The pseudo-rigid-body model, the free-body diagram, and the Lagrange method are all used together in this study to look into kinetostatics and dynamics. The water cycle algorithm is used to conduct structural optimization based on mathematical models. The prototype is fabricated by CNC milling, and physical tests are conducted. According to the findings for the resonant frequency, the analytical results well match the finite element analysis (FEA) results with an error of 8.44%. Besides, the measured resonant frequency was determined approximately 486 Hz, while the FEA yielded a result of 460.4 Hz. The discrepancy between the FEA and experimental results is 5.26%. The utilization of the design mechanism holds promise for the application of vibration-assisted polishing. [ABSTRACT FROM AUTHOR]

Origami-inspired mechanisms provide opportunities for deployable systems, including reflectarray antennas. There is a need for approaches to deploy and stabilize such arrays. Magnetic mechanisms show promise for meeting those needs and how methods for modelling their behaviour would facilitate their design and analysis. We demonstrate the existence of bistability in select configurations of magnetically stabilized hinges and characterize their equilibrium positions as a function of parameters estimated from simulation data for these mechanisms. Other relevant information such as potential energy, axial force data, angular position of unstable equilibria and transition values from bistability to monostability are also modelled. The results are verified through experimental torque and stability data for selected configurations of the mechanisms. This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'. [ABSTRACT FROM AUTHOR]

Multi‐stable structures can be reconfigured with fewer, lightweight, and less accurate actuators. This is because the attraction domain in the multi‐stable energy landscape provides both reconfiguration guidance and shape accuracy. Additionally, such structures can generate impulsive motion due to structural instability. Most multi‐stable units are planar structures, while spatial linkages can generate complex 3D motion and hold a more promising potential for applications. This study proposes a generalized approach to design a type of intrinsically multi‐stable spatial (IMSS) linkages with multiple prescriptible configurations, which are structurally compatible, and naturally stable at these states. It reveals that all over‐constrained mechanisms can be transformed into multi‐stable structures with the same design method. Single‐loop bi‐stable 4R and quadra‐stable 6R spatial linkages modules with intrinsic non‐symmetric stable states, which are transformed from fundamental kinematic linkage mechanisms unit such as Bennett and Bricard linkages, are designed to illustrate the basic idea and the superiority over the ordinary methods. Multi‐loop assembly by these IMSS linkage modules shows potential for practical applications that are required for the deployability and impulsivity of reconfiguration. Two preliminary design cases of a deployable tube and an impulsive gripper are experimentally presented to validate this applicability. Further promisingly, this design method of IMSS linkages paves the way for morphing platforms with lightweight actuation, high shape accuracy, high stiffness, and prescribed impulsive 3D motion. [ABSTRACT FROM AUTHOR]

This paper presents the development of a robotic ankle exoskeleton for human walking assistance. First, the biomechanical properties of a human ankle joint during walking are presented. Next, design of the robotic ankle exoskeleton is introduced. The exoskeleton is actuated by a novel parallel nonlinear elastic actuator. The cam-spring mechanism in the actuator can function as a parallel nonlinear spring with an adjustable stiffness, and the design of the cam profile curve is described. Additionally, an adaptive controller is proposed for the exoskeleton to generate a desired assistive torque according to the wearer's total weight. Finally, experiments are conducted to validate the effectiveness of the developed robotic ankle exoskeleton. The experimental results demonstrate that during a gait cycle, reductions of 42.7% and 40.1% of the peak and average currents of the driving motor in the actuator are observed, respectively, with the designed cam-spring mechanism. A peak assistive torque of 23.9 Nm can be provided for the wearers by the exoskeleton during walking. With the assistance provided by the exoskeleton, the average and peak soleus activities of the wearers during a gait cycle are decreased by 25.42% and 31.94%, respectively. [ABSTRACT FROM AUTHOR]

Decoupled compliant parallel mechanisms with isotropic legs possess many excellent performances, including ease of actuation, control, manufacture and mathematical analysis, as well as effective error compensation. Despite the advent of numerous isotropic compliant parallel mechanisms, their synthesis process predominantly relies on the empirical knowledge of engineers, with an absence of dedicated synthesis methodologies. This paper proposes the constraint algebra method, a novel synthesis method capable of autonomously exploring feasible constraint space for the synthesis. This method involves algebraic formulation of the constraints for the compliant modules, followed by solving constraint equations to find the feasible constraints and orientations, thereby facilitating the synthesis with intended performance characteristics. The multiplicity of solutions to the constraint equations enables the generation of diverse designs, including innovative configurations that are challenging to obtain via other methods and experience. Furthermore, by the consideration of machinability in several steps of synthesis, the optimal configuration can be selected for simplified manufacture. A design case has been monolithically prototyped and experimentally tested. The proposed methodology holds promise for potential extension to the synthesis of other types of compliant mechanisms. [ABSTRACT FROM AUTHOR]

This study presents a novel framework for the optimal design of compliant mechanisms, specifically addressing the structural drawbacks of conventional single-point or de facto hinges. The hinges often lead to structural instability and stress concentration while deriving maximum motion. To overcome these issues, we introduce a new method that can design stable and elastic domains connected by either revolute or prismatic joints. The new method, called sequential analysis based on the reaction force, can successfully eliminate weak hinge points while optimizing joint locations. The efficiency of developed methodology is validated through several numerical examples, yielding compliant mechanisms with suppressed hinges. [ABSTRACT FROM AUTHOR]

Creating a compliant mechanism that has a high displacement amplification ratio, a large workspace, low stress, and a high frequency is difficult. Thus, this paper used SolidWorks to design the gripper mechanisms using the series bridge-type (BT) compliant mechanism. Minitab software was used to create orthogonal arrays for the study. The finite element method (FEM) in ANSYS was used to analyze displacement and equivalent stress of the studying model. The Taguchi method was used to evaluate the influence of design variables. The grey relational analysis (GRA) method with MEREC weighting method was utilized to maximize displacement and minimize principal stress. In this investigation, the designed dimension consisted of the thickness of the flexure hinge (FH) was from 0.2 to 0.4 mm, the length of the FH increased from 3 mm to 4 mm, the distance between the centers of the two FHs changed from 0.8 mm to 1.2 mm depending on each position, and the radius between the rigid link and FHs increased from 0.4 to 0.8 mm. The outcomes of the FEM and analysis of signal-to-noise (S/N) of all of the models showed that the designed dimension had significant influenced on the displacement magnification ratio of the micro-gripper compliant mechanism. With an input displacement of 0.01 mm, the optimal displacement and equivalent stress were obtained at 0.62241 mm and 121.08 MPa, respectively, by the grey relational analysis. The optimal case is the third case, with the thickness of the FH was 0.2 mm, the length of the FH was 3 mm, the distance between the centers of the two flexure hinges was 1.2 mm, and the radius between the rigid link and flexure hinges was 0.8 mm. The make a decision criteria consisted of TOPSIS, SAW, WASPAS, and VIKOR techniques, all demonstrate that the third case was the best. [ABSTRACT FROM AUTHOR]

Fish have excellent swimming performance, and one key factor is their ability to autonomously adjust body stiffness, which can help them efficiently swim at different speeds and complex environments. At present, the variable‐stiffness design of robotic fish still suffers from structural complexity, severe deformation, and small variation range, which limits the application of variable‐stiffness theory in robotic fish. In this article, a variable‐stiffness tail is designed based on layer‐jamming for robotic fish, which can conveniently achieve online stiffness adjustment while maintaining the optimal stiffness distribution and the shape is unaffected. A modeling method for the tail is proposed by combining the mechanical characteristics of the layer‐jamming structure with the pseudo‐rigid body model. To validate the performance of the tail, a series of experiments are conducted, which show that the stiffness variation range of the tail is around 10 times, and the accuracy of the model in predicting the kinematics of the tail is also verified. Moreover, the thrust tests demonstrate that stiffness adjustment is beneficial for fish swimming at different frequencies. The proposed variable‐stiffness tail will promote the development of efficient underwater biomimetic robots. [ABSTRACT FROM AUTHOR]

The dimensional synthesis of compliant mechanisms (CMs) leverages the flexibility of their components to achieve precise motion and functionality. This study introduces a novel approach using the parametric fuzzy form of the Freudenstein equation with triangular fuzzy numbers (TFNs) to address the complexities and uncertainties inherent in CM design. By integrating fuzzy logic with advanced computational techniques such as Newton's method, the proposed methodology offers a robust framework for synthesizing CMs that can adapt to varying conditions. This approach enables the creation of flexible links modeled as fuzzy regions, allowing for optimized performance and reliability across a range of operational scenarios. Numerical examples illustrate the practical application and efficacy of the proposed methods, highlighting significant improvements in the design and synthesis of CMs. The integration of fuzzy logic in the synthesis process not only enhances the resilience of the mechanisms but also paves the way for future advancements in the field. This study demonstrates the potential of fuzzy logic principles in optimizing CM designs, ensuring they meet specific functional requirements with high precision. [ABSTRACT FROM AUTHOR]

The objective of the currentwork was to develop an all-electric distributed propulsion and flight control (DPFC) architecture that will have no more than 10-9 catastrophic failures per flight hour (pfh). The DPFC architecture was broken into four system design teams: (i) electrical power and distribution system, (ii) drive and power system, (iii) thermal management system, and (iv) flight control system. System designs were updated and iterated upon, working with reliability and safety analysis teams to develop compliant designs. The firm designs were reflected in a preliminary system safety assessment (PSSA) for initial verification of compliance. Additionally, design and analysis excursions are presented in which aircraft attributes were modified to investigate sensitivities to propulsion type, number of rotors, and control schemes. Excursion results found that all aircraft evaluated likely have paths to comply with the stringent, probabilistic catastrophic failure criteria. However, stability and control models showed large power transients that must be addressed, and PSSA results show that future work is needed in single load path structures, high voltage power storage and distribution, and motor/rotor overspeed protection. [ABSTRACT FROM AUTHOR]

Designing guidance mechanisms using bistable mechanisms with two stable positions is a common low-power solution for maintaining the guidance position without continuous external energy input. However, the coupling between kinematics and statics in compliant bistable mechanisms poses a challenge for their application in mechanism synthesis. To address this issue, this paper introduces the pole similarity transformation theory into the synthesis of compliant mechanisms and proposes a general synthesis method for planar serial-based compliant bistable mechanisms. This method models the compliant mechanism using the strain energy method and analyzes the bistable characteristics of the mechanism within its motion plane using the saddle point searching method. By doing so, the proposed method can identify stable positions without predetermined motion trajectories, making it more suitable for designing compliant bistable mechanisms with general planar motion. Additionally, this method utilizes the pole map to describe the stable positions of the rigid components in the compliant mechanism and establishes an information database for compliant bistable mechanisms. Through leveraging the pole similarity transformation, the pole maps of the mechanisms in the information database are matched with the pole map of the motion task, thus achieving the synthesis of planar serial-based compliant bistable mechanisms for the rigid-body guidance problem. The paper provides a detailed explanation of the mechanism synthesis process and demonstrates its application through a case study. [ABSTRACT FROM AUTHOR]

A rhombus-nested compliant amplification mechanism is proposed for versatile usages of precision actuators and force sensors with an easy tuning of stiffness. Such a monolithically planar rhombus-nested compliant mechanism has the dual functions of two-stage displacement or force amplification by changing the input and output ports. It features a large ratio of inter-stage stiffness, thus resulting in an enhanced amplification ratio, load capacity and dynamic bandwidth. The geometrically nonlinear analytical equations of displacement amplification ratio and input stiffness are derived in the presence of pronounced axially-loaded stiffening and kinematic-arching effects based on the beam constraint model. It allows an insightful evaluation of geometrically nonlinear deformation behaviors sensitive to structural dimensions in a parametric way. Insights into geometrically nonlinear behaviors in the case of large-stroke and axially-loaded motions are discussed as well. A proof-of-concept prototype with embedded piezoelectric stacks is fabricated with the dimensions of 74mm × 60mm × 10 mm. The dual functions of precision actuator with amplified motion strokes and force sensor with enhanced sensitivity are experimentally demonstrated. [Display omitted] • A monolithically rhombus-nested compliant amplification mechanism is designed. • Geometrically nonlinear analytical model of amplification ratio is derived. • The dual functions of a precision actuator and force sensor are demonstrated. [ABSTRACT FROM AUTHOR]

To ensure the manufacturability of compliant mechanisms, this paper presents a new approach for optimal design of electro-thermo-mechanical microactuators by employing minimum length scale constraints. A sequential coupling method is adopted to carry out finite element analysis for electric-thermal-mechanical coupling multiphysics. The inflection point fields of the solid and void phases are identified by structural indicator functions. The minimum length scales of the solid and void phases are adopted as constraints. The optimization objective is designed to maximize the output displacements of electro-thermo-mechanical microactuators. The validity of the proposed optimal design method is demonstrated through several numerical examples. In the optimal designs obtained by the proposed method, the minimum length scales of the two phases can be properly controlled. The electro-thermo-mechanical microactuator's output displacements decrease when the allowable value of the minimum length scale is increased. The effects of different mesh discretizations and output spring stiffnesses on the optimized designs are discussed. [ABSTRACT FROM AUTHOR]

In the present work, a parallel continuum manipulator for trunk rehabilitation tasks for patients who have suffered a stroke was analyzed and redesigned. The manipulator had to perform active assistance exercises for the motor recovery of the patient. Based on this background, a series of requirements were defined, which determined the design framework during the modeling of the manipulator. Finally, an improved prototype was built and tested to verify that the model can properly characterize the behavior of the manipulator. Such tests were carried out using a self-made dummy that replicates the simplifying hypotheses and conditions assumed in the mathematical model. [ABSTRACT FROM AUTHOR]

Cell micromanipulation is an important technique in the field of biomedical engineering. Microgrippers play a crucial role in connecting macroscopic and microscopic objects in micromanipulation systems. However, since the operated biological cells are deformable, vulnerable, and typically distributed in sizes ranging from micrometers to millimeters, it poses a huge challenge to microgripper performance. To solve this problem, this paper develops a dual-driven piezoelectric microgripper with a high displacement amplification ratio, large stroke, and parallel gripping. By adopting modular configuration, three kinds of flexure-based mechanisms, including the lever mechanism, Scott–Russell mechanism, and parallelogram mechanism are connected in series to realize three-stage amplification, which effectively makes up for the shortage of small output displacement of the piezoelectric actuator. At the same time, the use of the parallelogram mechanism also isolates the parasitic rotation movement, and realizes the parallel movement of the gripping jaws. In addition, the kinematics, statics, and dynamics models of the microgripper are established by using the pseudo-rigid body and Lagrange methods, and the key geometric parameters are also optimized. Finite element simulation and experimental tests verify the effectiveness of the developed microgripper. The results show that the developed microgripper allows an amplification ratio of 46.4, a clamping stroke of 2180 μ m, and a natural frequency of 203.1 Hz. Based on the developed microgripper, the nondestructive micromanipulation of zebrafish embryos is successfully realized. [ABSTRACT FROM AUTHOR]

Copyright of Technisches Messen is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A rotary vibration-assisted polishing device (RVAPD) is designed to enhance polishing force by converting PZT's linear motion into the rotary motion of a central platform via a flexible mechanism, improving material surface quality. The RVAPD is optimized, simulated, and tested to meet high-frequency and large-amplitude non-resonant vibration polishing requirements. Its structure, designed using theoretical models and finite element software, offers a wide range of polishing parameters. Performance parameters are validated through open-loop tests, confirming effectiveness in polishing experiments. The lever mechanism and Hoeckens connection enhance vibration parameters and motion efficiency, reducing surface flaws in SiC and improving uniformity. Adjusting the RVAPD structure and using the proposed method significantly improve SiC surface quality. [ABSTRACT FROM AUTHOR]

Axial micromotion between bone fragments can stimulate callus formation and fracture healing. In this study, we propose a novel mechanically compliant locking plate which achieves up to 0.6 mm of interfragmentary motion as flexures machined into the plate elastically deflect under physiological load. We investigated the biomechanical performance of three compliant plate variations in comparison to rigid control plates with small and large working lengths in a comminuted bridge plating scenario using humeral diaphysis surrogates. Under static axial loading, average interfragmentary motion was 6 times larger at 100 N (0.38 vs. 0.05 mm) and nearly three times larger at 350 N (0.58 vs. 0.2 mm) for compliant plates than rigid plates, respectively. Compliant plates delivered between 2.5 and 3.4 times more symmetric interfragmentary motion than rigid plates (p < 0.01). The bi‐phasic stiffness of compliant pates provided 74%–96% lower initial axial stiffness up to approximately 100 N (p < 0.01), after which compliant plate stiffness was similar to rigid plates with increased working length (p > 0.3). The strength to failure of compliant plates under dynamic loading was on average 48%–55% lower than rigid plate groups (p < 0.01); however, all plates survived cyclic fatigue loading of 100,000 cycles at 350 N. This work characterizes the improvement in interfragmentary motion and the reduction in strength to failure of compliant plates compared to control rigid plates. Compliant plates may offer potential in comminuted fracture healing due to their ability to deliver symmetric interfragmentary motion into the range known to stimulate callus formation while surviving moderate fatigue loading with no signs of failure. [ABSTRACT FROM AUTHOR]

AbstractA tripod is a classical lower mobility parallel manipulator with three degrees of freedom. The usual geometrical constraints enforce a type of motion with two rotations on a horizontal plane and a translational motion in a vertical direction. These devices are applicable where a task requires a precise orientational motion. Nevertheless, some parasitic motions occur on the constrained degrees of freedom. Parallel Continuum Manipulators are devices where some elements have been replaced by slender rods whose deformation is source of mobility, allowing the elimination of some of the kinematic joints. This type of closed-loop compliant mechanisms have some features that can be useful in certain applications, e.g., the deformed state introduces a certain preload that avoids backslash, they have an inherent compliance that can be useful in some delicate tasks, and a certain control on wrench applied can be obtained. In this article, the comprehensive kinetostatic analysis of a tripod-type parallel continuum manipulator, 3P¯FS, is explained and compared with that of its rigid counterpart 3P¯RS. Workspace and singularity locus is obtained, positioning accuracy and wrench generation are evaluated experimentally. [ABSTRACT FROM AUTHOR]

The ultra-precision field is popular for its micro-nanometer positioning accuracy and large working stroke. Piezoelectric actuators based on the stick-slip operational principle exhibit superior performance characteristics, making them stand out with unique advantages in this field. This paper provides a comprehensive review of the developments in stick-slip piezoelectric actuators over recent years. Starting with a detailed explanation of their operating principles, the article proceeds with a brief introduction to the more commonly used driving waveforms and their applications. Subsequently, various design and optimization technologies for existing compliant mechanisms are presented. Furthermore, stick-slip piezoelectric actuators are categorized based on different motion forms, including linear, rotary, and multi-degree of freedom types. Each category is thoroughly examined in terms of structural design and performance features. Following this, the discussion shifts toward controller method research and friction modeling analysis, featuring a particular emphasis on the advancements related to displacement backlash suppression studies. This systematic summary aims to provide a reference for researchers within related fields, thereby facilitating the further development and application of stick-slip piezoelectric actuators. [ABSTRACT FROM AUTHOR]

This paper presents a new approach that automates the tuning process in topology optimization of parameters that are traditionally defined by the user. The new method draws inspiration from hyperparameter optimization in machine learning. A new design problem is formulated where the topology optimization hyperparameters are defined as design variables and the problem is solved by surrogate optimization. The new design problem is nested, such that a topology optimization problem is solved as an inner problem. To encourage the identification of high-performing solutions while limiting the computational resource requirements, the outer objective function is defined as the original objective combined with penalization for intermediate densities and deviations from the prescribed material consumption. The contribution is demonstrated on density-based topology optimization with various hyperparameters and objectives, including compliance minimization, compliant mechanism design, and buckling load factor maximization. Consistent performance is observed across all tested examples. For a simple two hyperparameter case, the new framework is shown to reduce amount of times a topology optimization algorithm is executed by 90% without notably sacrificing the objective compared to a rigorous manual grid search. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering & Architectural Faculty of Eskisehir Osmangazi University / Eskişehir Osmangazi Üniversitesi Mühendislik ve Mimarlık Fakültesi Dergisi is the property of Eskisehir Osmangazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In minimally invasive surgery, grippers are essential for tissue manipulation. However, in commercial tendon‐driven systems, challenges remain, including tendon fatigue and bulkiness. Promising alternatives are magnetically actuated systems, offering contactless steering but limited forces. To overcome this, a miniaturized, locally actuated magnetic gripper with variable stiffness is presented. The gripper employs thin planar coils (75 μm) and a radially magnetized plunger, enabling local actuation and enhanced orientation control. The variable stiffness compliant mechanism made from shape‐memory polymer facilitates different gripping strategies. In its rigid state, pulsed pulling forces of 340 mN and continuous forces of 90 mN are achieved, exceeding the gripper weight by factors of 70 and 18, respectively. The soft state, with a fast response time of 20 ms, enables soft gripping of various targets, including moving ones and rat tissue samples. Demonstrating the applicability, contactless steering and target retrieval within a stomach phantom is showcased. This study introduces promising improvements to magnetically actuated grippers for surgical procedures, addressing key challenges in current designs. [ABSTRACT FROM AUTHOR]

Compliant mechanism work based on the elasticity of material, dimension of the compliant mechanisms and the shape of flexure hinge. In order to larger workspace, most published works use theoretical models to determine the displacement amplification of the mechanical systems, which is very difficult to do. A simpler method that can still achieve efficiency while designing a mechanism with high displacement gain and low stress that ensures a stable working structure is to use combined grey relational analysis Taguchi method is based on the results of finite element analysis in ANSYS. To do this, first select the design variables for the symmetric differential lever displacement amplifier model. Next step, use Minitab software to design 27 cases. Then use SolidWorks to design 27 models of symmetrical differential displacement amplifier. Next to finite element analysis in ANSYS to obtain displacements and stresses of the symmetrical differential lever compliant mechanism with circular flexure hinge. The results obtained from the finite element model are used for optimization by grey relationship analysis combined with the Taguchi method. The FEM results indicated that the designed variables significantly affected on the displacement and stress of the symmetrical differential lever displacement magnification compliant mechanism. The problem was also confirmed by grey relational analysis with Taguchi method. The predicted and optimal values of the displacement were 0.11276 mm and 0.1179 mm, with error of 4.36%. The input displacement was 0.01 mm, while the displacement magnification ratio was 11.79 times. The results verified by decision-making criteria: TOPSIS method, MOORA method and EDAS method. [ABSTRACT FROM AUTHOR]

Using soft materials in robotic mechanisms has become a common solution to overcome many challenges associated with the rigid bodies frequently used in robotics. Compliant mechanisms allow the robot to adapt to objects and perform a broader range of tasks, unlike rigid bodies that are generally designed for specific applications. However, soft robotics presents its own set of challenges in both design and implementation, particularly in sensing and control. These challenges are abundant when dealing with the force control problem of a compliant gripping mechanism. The ability to effectively regulate the applied force of a gripper is a critical task in many control operations, as it allows the precise manipulation of objects, which drives the need for enhanced force control strategies for soft or flexible grippers. Standard sensing techniques, such as motor current monitoring and strain-based sensors, add complexities and uncertainties when establishing mathematical models of soft grippers to the required gripping forces. In addition, the soft gripper creates a complex non-linear system, compounded by adding an adhesive-type sensor. This work develops a unique visual force sensor trained on synthetic data generated using finite element analysis (FEA) and implemented by integrating a non-linear model reference adaptive controller (MRAC) to control gripping force on a fixed 6-DOF robot. The robot can be placed on a mobile platform to perform various tasks. The virtual FEA sensor and controller, combined, are termed virtual reference adaptive control (VRAC). The VRAC was compared to other methods and achieved comparable control sensing and control performance while reducing the complexity of the sensor requirements and its integration. The VRAC strategy effectively controlled the gripping force by driving the dynamics to match the desired performance after a limited amount of training cycles. The controller proposed in this work was designed to be generally applicable to most objects that the gripper will interact with and easily adaptable to a wide variety of soft grippers. [ABSTRACT FROM AUTHOR]

This article presents a generalized model of two-axis flexure hinges based on quadratic rational Bézier curve. The generalized closed-form compliance equations are derived based on the virtual work theory and the superposition relationship of the deformation. Then, how to determine the number of sensitive axes, the location of the primary and secondary sensitive axes, and the configuration of the notch profile are discussed. There are 20 types of notch profiles derived from single or mixed, symmetrical or asymmetrical curves. And, the correctness of the compliance equations is verified by finite-element analysis. The maximum relative error does not exceed 10%. Finally, the precision of rotation, the maximum stress, and the effect of structural parameters on the compliance are analyzed. The results show that for two-axis flexure hinges with a flush single curve notch profile, the proximity of the center of rotation to the load end does not significantly affect the axial compliance as well as the torsional compliance. For hybrid two-axis flexure hinges with symmetric structure, the ability to maintain the center of rotation under lateral forces is better than that under the same torque. The proposed generalized model provides a reference for the design of spatial compliant mechanisms. [ABSTRACT FROM AUTHOR]

Current design methods for flexure (or compliant) mechanisms regard stress as a secondary, limiting factor. This is remarkable because stress is also known as a useful design parameter. In this paper we propose the Stress And Geometry (STAGE) method, to design the geometry of a flexure mechanism together with a desired stress field. From this design, the stress-free to-be-fabricated geometry is computed using the inverse finite element method. To demonstrate the potential of the method, the geometry of the well-known crossed-flexure pivot is taken as example. We first show how this mechanism can be redesigned for the same functional geometry with various internal stresses. This results for a specific choice of stress field in a design of a crossed-flexure pivot with 23% lower peak stresses during motion as compared to the known designs, for a ± 45° rotation. We then present a second example, of a Folded Leaf Spring (FLS). With a parameter sweep the optimal stress field is calculated, showing a peak stress reduction of 28% during motion. This result was validated with an experiment, showing a normalized mean absolute error of 5.5% between experiment and theory. With a second experiment it was verified that the functional geometry of the FLS with internal stresses was equal to the one without internal stresses, with geometric deviations smaller than half the thickness of the flexures. • A method is proposed to design the geometry and stress of flexure mechanisms simultaneously. • The peak stress in a Crossed-Flexure Pivot has been reduced by 23% using the proposed method. • This stress reduction is achieved without changing the functional geometry of the mechanism. • Similarly, the peak stress in a Folded Leaf Spring has been reduced by 28%. • Empirical tests validate that the stresses are reduced without changing the functional geometry. • The fabrication method used in the article is proven in Industry (wire-EDM). [ABSTRACT FROM AUTHOR]

Innovative designs such as morphing wings and terrain adaptive landing systems are examples of biomimicry and innovations inspired by nature, which are actively being investigated by aerospace designers. Morphing wing designs based on Variable Geometry Truss Manipulators (VGTMs) and articulated helicopter robotic landing gear (RLG) have drawn a great deal of attention from industry. Compliant mechanisms have become increasingly popular due to their advantages over conventional rigid-body systems, and the research team led by the second author at Toronto Metropolitan University (TMU) has set their long-term goal to be exploiting these systems in the above aerospace applications. To gain a deeper insight into the design and optimization of compliant mechanisms and their potential application as alternatives to VGTM and RLG systems, this study conducted a thorough analysis of the design of flexible hinges, and single-, four-, and multi-bar configurations as a part of more complex, flexible mechanisms. The investigation highlighted the flexibility and compliance of mechanisms incorporating circular flexure hinges (CFHs), showcasing their capacity to withstand forces and moments. Despite a discrepancy between the results obtained from previously published Pseudo-Rigid-Body Model (PRBM) equations and FEM-based analyses, the mechanisms exhibited predictable linear behavior and acceptable fatigue testing results, affirming their suitability for diverse applications. While including additional linkages perpendicular to the applied force direction in a compliant mechanism with N vertical linkages led to improved factors of safety, the associated increase in system weight necessitates careful consideration. It is shown herein that, in this case, adding one vertical bar increased the safety factor by 100 N percent. The present study also addressed solutions for the precise modeling of CFHs through the derivation of an empirical polynomial torsional stiffness/compliance equation related to geometric dimensions and material properties. The effectiveness of the presented empirical polynomial compliance equation was validated against FEA results, revealing a generally accurate prediction with an average error of 1.74%. It is expected that the present investigation will open new avenues to higher precision in the design of CFHs, ensuring reliability and efficiency in various practical applications, and enhancing the optimization design of compliant mechanisms comprised of such hinges. A specific focus was put on ABS plastic and aluminum alloy 7075, as they are the materials of choice for non-load-bearing and load-bearing structural components, respectively. [ABSTRACT FROM AUTHOR]

Compliant mechanisms with embedded piezoelectric actuators have widely been used in high vibration environments, which brings a requirement that the fundamental frequency should be greater than the external excitation frequency to avoid resonance. Existing topology optimization methods focus on enhancing the output stroke of compliant mechanisms while ignoring their dynamic properties. Hence, this work presents a concurrent optimization method of compliant structures embedded with movable piezoelectric actuators considering both the output stroke and dynamic properties. A density-based material interpolation scheme is developed to represent material properties in different sub-domains occupied by compliant mechanisms or actuators, and the topology of host compliant mechanisms and position of actuators are optimized simultaneously through designing the density field and geometric variables. To enhance dynamic properties of the mechanism, the fundamental frequency constraint is introduced into the standard compliant mechanism optimization formulation, in which the objective function is output displacement, and the constraint is volume fraction. The p-norm approximation function is adopted to alleviate the non-differentiability arising from the repeated eigenvalues and mode switching during the iterative process. Furthermore, using the adjoint method, the sensitivities of the objective function and constraints with respect to design variables are derived for the gradient-based optimizer. Several numerical examples are investigated to verify the effectiveness of the proposed optimization method and demonstrate the influence of the fundamental frequency constraints on the optimized results. The topologic results illustrate that the proposed method can attain a reasonable design, in which the output stroke is maximized and the fundamental frequency constraint is satisfied. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a Physics-Informed Neural Networks (PINNs)-based Topology optimization method that is free from the usual finite element analysis and is applicable for both self-adjoint and non-self-adjoint problems. This approach leverages the continuous formulation of TO along with the continuous adjoint method to obtain sensitivity. Within this approach, the Deep Energy Method (DEM)—a variant of PINN-completely supersedes traditional PDE solution procedures such as a finite-element method (FEM) based solution process. We demonstrate the efficacy of the DEM-based TO framework through three benchmark TO problems: the design of a conduction-based heat sink, a compliant displacement inverter, and a compliant gripper. The results indicate that the DEM-based TO can generate optimal designs comparable to those produced by traditional FEM-based TO methods. Notably, our DEM-based TO process does not rely on FEM discretization for either state solution or sensitivity analysis. During DEM training, we obtain spatial derivatives based on Automatic Differentiation (AD) and dynamic sampling of collocation points, as opposed to the interpolated spatial derivatives from finite element shape functions or a static collocation point set. We demonstrate that, for the DEM method, when using AD to obtain spatial derivatives, an integration point set of fixed positions causes the energy loss function to be not lower-bounded. However, using a dynamically changing integration point set can resolve this issue. Additionally, we explore the impact of incorporating Fourier Feature input embedding to enhance the accuracy of DEM-based state analysis within the TO context. The source codes related to this study are available in the GitHub repository: . [ABSTRACT FROM AUTHOR]

A wire beam is a single-translation constraint along its axial direction. It offers many applications in compliant mechanisms, such as being a transmitting/decoupling element connected to a linear actuator and being a fundamental constitutive element to design complex compliant joints and mechanisms. It is desired to find an alternative leaf beam single-translation constraint to equal a wire beam in order to improve the manufacturability and robustness to external loading. In this paper, we propose and model a new single-translation constraint compliant module, I-shape leaf beam design, to compare with a corresponding L-shape leaf beam design reported in the literature. Two spherical (S) joints using three I-shape leaf beams and three L-shape leaf beams, respectively, are then analytically modeled and analyzed. Three key geometric parameters are adopted to thoroughly assess four performance indices of each S joint, including stiffness ratio, rotation radius error, coupling motion, and parasitic motion. It shows that the I-shape leaf beam-based S joint performance indices are generally 10 times better than those of the L-shape leaf beam-based S joint. For each S joint, the optimal parameters are found under the given conditions. Finally, experimental tests are carried out for a fabricated S joint prototype using the I-shape leaf beams, the results from which verify the accuracy of the proposed analytical model and the fabrication feasibility. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic optimization method capable of optimizing the dynamic responses of a compliant parallel mechanism (CPM), in terms of its multiple primary resonant modes, is presented. A novel two-term objective function is formulated based on the specific frequency range and targeted ratios. The first term of the function is used to optimize the first resonant mode of the CPM, within a specific frequency range. The obtained frequency value of the first mode is used in the second term to define the remaining resonant modes to be optimized in terms of targeted ratios. Using the proposed objective function, the resonant modes of a CPM can be customized for a specific purpose, overcoming the limitations of existing methods. A 6-degree-of-freedom (DoF) CPM with decoupled motion is synthesized, monolithically prototyped, and investigated experimentally to demonstrate the effectiveness of the proposed function. The experimental results showed that the objective function is capable of optimizing the six resonant modes within the desired frequency range and the targeted ratios. The highest deviation between the experimental results and the predictions among the six resonant modes is found to be 9.42%, while the highest deviation in the compliances is 10.77%. The ranges of motions are found to be 10.0 mm in the translations, and 10.8° in the rotations. [ABSTRACT FROM AUTHOR]

To further enhance the performance of the fast tool servo (FTS) system in terms of stroke, load capacity, and application area, this paper proposes a novel fast tool servo device driven by a voice coil motor (VCM), based on a three-segment uniform corrugated flexure (CF) guiding mechanism, with a large stroke, high accuracy, and high dynamics. To describe the unified static characteristics of such device, the compliance matrix method is applied to establish its model, where the influence of CF beam structural parameters on the FTS device is investigated in detail. Furthermore, resolution and positioning accuracy tests are conducted to validate the features of the system. The testing results indicate that the maximum stroke of the FTS device is up to 3.5 mm and the positioning resolution values are 3.6 μm and 2.4 μm for positive and negative stroke, respectively, which further verifies the device's effectiveness and promising application prospect in ultra-precision microstructure machining. [ABSTRACT FROM AUTHOR]

This paper proposes a "planning and control" scheme for a compliant mechanism (CM) based on a pneumatic actuator (PAC) with hysteresis nonlinearity and full-state constraints. In the planning part, a novel direct inverse model is presented to compensate for hysteresis nonlinearity, enabling more accurate planning of the desired air pressure based on the desired contact force. In the control part, by fusing fuzzy logic systems (FLSs) and an extended state observer (ESO), a fuzzy ESO is developed to observe the external disturbance and the rate of change of the air pressure. Additionally, the challenges in the controller design caused by full-state constraints are overcome by constructing barrier Lyapunov functions (BLFs). It is proved that all signals of the closed-loop system are bounded, and the tracking error of the air pressure can converge to a small neighborhood of the origin. Finally, the effectiveness and robustness of the proposed method are verified by hardware experiments, which also show that the root mean square errors of force control accuracies are within 2N, achieving satisfactory force control effects. [ABSTRACT FROM AUTHOR]

To effectively isolate low-frequency vibrations, we present a rigid–flexible coupling quasi-zero-stiffness (QZS) vibration isolator with high-static-low-dynamic stiffness (HSLDS) characteristics. Specifically, the QZS isolator is realized by the development of a compliant constant-force mechanism, formed by parallelly combining a diamond-shape mechanism and a nonlinear bi-stable beam in parallel. To evaluate performance of the QZS isolator, we derived an analytical force–displacement model and dynamic model based on pseudo-rigid body method and Lagrange's equations. Then, finite element analysis was performed in Workbench to verify theoretical analysis and identify the optimal design parameters. Furthermore, the dynamic responses of the QZS isolator are established with the harmonic balance method. Finally, the relationships among displacement transmissibility and factors including damping, BSB, payload mass, and material property are discussed. The results have shown that our QZS isolator design can effectively isolate vibrations in low frequency. [ABSTRACT FROM AUTHOR]

A three-stage displacement amplification microgripper system based on compliant mechanisms was designed for microassembly and microoperation tasks. The static mechanical models of the microgripper system were established, and the mechanical characteristics of the output displacements, stresses, and strains of the microgripper system were comprehensively simulated and analyzed. It was demonstrated that the microgripper system demonstrated excellent leveling performance, with the stresses and strains being concentrated at the flexible hinges. Subsequently, the tracking control experiments of the finger displacement and gripping force of the microgripper system were conducted using sinusoidal signals, variable amplitude signals, and frequency signals. It was clearly illustrated that the dynamic performances of the microgripper system are remarkable, and the standard deviation of the tracking error of the finger displacement is no more than 0.2 µm, while that of the gripping force is 0.35 mN under closed-loop conditions. The designed microgripper system achieves accurate control of displacements and gripping forces, effectively fulfilling the requirements of high-precision microassembly tasks. [ABSTRACT FROM AUTHOR]

Semi-active adjustable constant force mechanisms (ACFMs) are an emerging alternative in applications where energy-efficient control of constant force environments is required. However, there is a lack of design strategies in the literature for semi-active ACFMs. This study addresses this gap by presenting a design strategy for ACFMs that semi-actively tunes the constant force by structural control. A design framework is presented, which consists of an optimization of a high slenderness large stroke constant force mechanism (CFM) followed by a parametric study on adjusting constant force through slenderness reduction by repositioning the boundary condition location. The design framework was able to change constant force ranging from two to four times with a stroke of 11-26% of the mechanism footprint. A selected design with a larger force magnitude was fabricated and experimentally tested, demonstrating a change in constant force of 2.01 times, which is comparable to that of active control designs and improved compactness, i.e., stroke of 11% of the footprint of the mechanism. In conclusion, the proposed ACFM design framework maximizes the initial CFM stroke and achieves constant force tuning by changing beam slenderness, resulting in compact and efficient ACFM designs. [ABSTRACT FROM AUTHOR]

The manipulation of compliant objects by robotic systems remains a challenging task, largely due to their variable shapes and the complex, high-dimensional nature of their interaction dynamics. Traditional robotic manipulation strategies struggle with the accurate modeling and control necessary to handle such materials, especially in the presence of visual occlusions that frequently occur in dynamic environments. Meanwhile, for most unstructured environments, robots are required to have autonomous interactions with their surroundings. To solve the shape manipulation of compliant objects in an unstructured environment, we begin by exploring the regression-based algorithm of representing the high-dimensional configuration space of deformable objects in a compressed form that enables efficient and effective manipulation. Simultaneously, we address the issue of visual occlusions by proposing the integration of an adversarial network, enabling guiding the shaping task even with partial observations of the object. Afterwards, we propose a receding-time estimator to coordinate the robot action with the computed shape features while satisfying various performance criteria. Finally, model predictive controller is utilized to compute the robot's shaping motions subject to safety constraints. Detailed experiments are presented to evaluate the proposed manipulation framework. Our MPC framework utilizes the compressed representation and occlusion-compensated information to predict the object's behavior, while the multi-objective optimizer ensures that the resulting control actions meet multiple performance criteria. Through rigorous experimental validation, our approach demonstrates superior manipulation capabilities in scenarios with visual obstructions, outperforming existing methods in terms of precision and operational reliability. The findings highlight the potential of our integrated approach to significantly enhance the manipulation of compliant objects in real-world robotic applications. • A parametric shape descriptor to efficiently characterize 3D deformations based on online curve/surface fitting. • A robust shape prediction network based on adversarial neural networks to compensate visual occlusions. • An optimization-based estimator to approximate the deformation Jacobian matrix and satisfy various performance constraints. • An MPC-based controller to guide the shaping motions while simultaneously solving saturation, workspace, and obstacle constraints. [ABSTRACT FROM AUTHOR]

This paper details the design and preliminary demonstrations for a compact climbing robot named EEWOC (Extended-reach Enhanced Wheeled Orb for Climbing). This novel platform utilizes the EEMMMa limb (Elastic Extending Mechanism for Mobility and Manipulation), detailed in previous work. This highly extendable and bendable robotic limb utilizes a unique tape spring structure for long reach in a small, lightweight package. EEWOC combines this limb with additional degrees of freedom and two magnetic grippers to allow it to ascend vertical metal surfaces by consecutively extending and gripping. It is also equipped with wheels for horizontal mobility. A key advantage of this system is EEWOC's ability to bend to place its grippers around obstacles or corners and above ledges. The prototype is small and lightweight, with a profile of 25x30x30 cm and weight of 1.8 kg, while able to extend its limb up to 1.2 m away. With versatile movement options, EEWOC has the potential to fully traverse large metal structures such as ships or buildings for use in inspection tasks. This paper presents a detailed view of the overall system and mechanism design, and successful climbing demonstrations are shown on steel structures. The paper concludes by detailing EEWOC's future capabilities and additional tests and theories needed to refine its maneuvers and control.

Abstract Multi‐stable structures can be reconfigured with fewer, lightweight, and less accurate actuators. This is because the attraction domain in the multi‐stable energy landscape provides both reconfiguration guidance and shape accuracy. Additionally, such structures can generate impulsive motion due to structural instability. Most multi‐stable units are planar structures, while spatial linkages can generate complex 3D motion and hold a more promising potential for applications. This study proposes a generalized approach to design a type of intrinsically multi‐stable spatial (IMSS) linkages with multiple prescriptible configurations, which are structurally compatible, and naturally stable at these states. It reveals that all over‐constrained mechanisms can be transformed into multi‐stable structures with the same design method. Single‐loop bi‐stable 4R and quadra‐stable 6R spatial linkages modules with intrinsic non‐symmetric stable states, which are transformed from fundamental kinematic linkage mechanisms unit such as Bennett and Bricard linkages, are designed to illustrate the basic idea and the superiority over the ordinary methods. Multi‐loop assembly by these IMSS linkage modules shows potential for practical applications that are required for the deployability and impulsivity of reconfiguration. Two preliminary design cases of a deployable tube and an impulsive gripper are experimentally presented to validate this applicability. Further promisingly, this design method of IMSS linkages paves the way for morphing platforms with lightweight actuation, high shape accuracy, high stiffness, and prescribed impulsive 3D motion.