Bistable Compliant Mechanism Research Articles

Task-driven geometric synthesis method of a bistable compliant mechanism for the rigid guidance problem

Abstract. Compliant bistable mechanisms are specialized mechanisms that have specific self-locking characteristics in two positions. They are widely used in aerospace, micro-electromechanical systems, and high-precision manufacturing. The coupling of kinematic with elastomechanical behaviors of compliant mechanisms, known as kinetostatics, increases the difficulty of synthesizing compliant mechanisms. Currently, most research relies on optimization approaches to find compliant mechanisms that meet motion requirements. To address this challenge, this paper proposes a geometric synthesis method for compliant bistable mechanisms to solve the rigid guidance problem. The pole similarity transformation characteristics of planar beams and the static equilibrium characteristic of bistable mechanisms at stable positions are utilized to decouple the kinematic synthesis and static analysis. The proposed method introduces a task-driven synthesis process, where the critical structural parameters in compliant mechanisms are determined based on the desired guidance positions of motion tasks. This approach eliminates the need for a tedious and time-consuming iterative optimization process. The resulting bistable mechanisms have two stable positions that correspond to the desired guidance positions of the motion task. To illustrate the effectiveness of the geometric synthesis method, a two-position problem of a compliant bistable mechanism is provided as an example.

The synthesis method of series-based bistable compliant mechanisms for rigid-body guidance problem based on geometrical similarity transformation of pole maps

Abstract 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.

Complibot: A compliant external pipe climbing robot

The article presents the design of Complibot, a robot with a novel gripper for pipe climbing. The mechanism of the gripper involves the use of a bistable buckled beam, which is a type of bistable compliant mechanism. The bistable buckled beam in the gripper is alternately actuated between its gripped and ungripped states using a camshaft and lever mechanism, which is powered by a single DC motor. The design parameters associated with the gripper are obtained both experimentally and numerically. A proper selection of design parameters helps in the efficient functioning of the gripper. After the design of the gripper, two such grippers are fabricated and attached to each other by two stepper motor-driven lead screws to make a pipe climbing robot with inchworm locomotion. The mobility of the robot is controlled by an Arduino Uno microcontroller after the electronic components have been integrated. Finally, Complibot is subjected to a series of tests to establish its maximum load-carrying capacity when climbing a polyvinyl chloride (PVC) pipe. Complibot is found to perform satisfactorily without slipping while climbing a PVC pipe with a diameter of 105–115 mm, a velocity of 0.2 m/min, a power consumption of 18.58 W, a maximum load-carrying capacity of 114.64 N, and a payload to weight ratio of 0.52.

A novel bistable device to study mechanosensitive cell responses to instantaneous stretch

The behavior of cells and tissues in vivo is determined by the integration of multiple biochemical and mechanical signals. Of the mechanical signals, stretch has been studied for decades and shown to contribute to pathophysiological processes. Several different stretch devices have been developed for in vitro investigations of cell stretch.In this work, we describe a new 3D-printed uniaxial stretching device for studying cell response to rapid deformation. The device is a bistable compliant mechanism holding two equilibrium states—an unstretched and stretched configuration—without the need of an external actuator. Furthermore, it allows multiple simultaneous measurements of different levels of stretch on a single substrate and is compatible with standard immunofluorescence imaging of fixed cells as well as live-cell imaging.To demonstrate the effectiveness of the device to stretch cells, a test case using aligned myotubes is presented. Leveraging material area changes associated with deformation of the substrate, changes in nuclei density provided evidence of affine deformation between cells and substrate. Furthermore, intranuclear deformations were also assessed and shown to deform non-affinely.As a proof-of-principle of the use of the device for mechanobiological studies, we uniaxially stretched aligned healthy and dystrophic myotubes that displayed different passive mechanical responses, consistent with previous literature in the field. We also identified a new feature in the mechanoresponse of dystrophic myotubes, which is of potential interest for identifying the diseased cells based on a quick mechanical readout. While some applications of the device for elucidating passive mechanical responses are demonstrated, the simplicity of the device allows it to be potentially used for other modes of deformation with little modifications.

Design of Deployable Structures by Using Bistable Compliant Mechanisms.

A deployable structure can significantly change its geometric shape by switching lattice configurations. Using compliant mechanisms as the lattice units can prevent wear and friction among multi-part mechanisms. This work presents two distinctive deployable structures based on a programmable compliant bistable lattice. Several novel parameters are introduced into the bistable mechanism to better control the behaviour of bistable mechanisms. By adjusting the defined geometry parameters, the programmable bistable lattices can be optimized for specific targets such as a larger deformation range or higher stability. The first structure is designed to perform 1D deployable movement. This structure consists of multi-series-connected bistable lattices. In order to explore the 3D bistable characteristic, a cylindrical deployable mechanism is designed based on the curved double tensural bistable lattice. The investigation of bistable lattices mainly involves four types of bistable mechanisms. These bistable mechanisms are obtained by dividing the long segment of traditional compliant bistable mechanisms into two equal parts and setting a series of angle data to them, respectively. The experiment and FEA simulation results confirm the feasibility of the compliant deployable structures.

Application of Chain Beam Constraint Model in numerical design Bistable compliant mechanisms

Bistable compliant mechanism is a monolithic part and jointless in the structure, is utilized due to saving energy, precious in operation, and reducing maintenance costs. This mechanism work based on the compression and tension of the flexural beam. Most calculation methods assist the mechanism's characteristics to have challenges because of the nonlinear behavior of the structure. This paper employs the CBCM (Chained Beam Constraints Model) method to analyze and evaluate Bistable compliant mechanisms. The flexural beam of the mechanism is divided into many segments for evaluating the compliant mechanism behavior. This method is verified with the finite element method and the results show insignificant errors. CBCM assists in the design of the compliant Bistable mechanism with high accuracy in a short time.

A Switchable Dual‐Mode Actuator Enabled by Bistable Structure

Soft actuators are favored due to their flexibility and adaptability, but are limited to single actuation mode. Herein, a novel soft actuator with a dual‐kinestate performance is proposed. By subtly integrating a bistable compliant mechanism with artificial muscles, the soft actuator is capable of switching between binary motion and continuous motion with accurate output. Functions of overcoming external interference and regulating the snapping time are realized with programmed voltages. Two applications utilizing the switchable kinestate are illustrated, including a mechanical encryption display system with one actuator and an amplitude modulation system with two actuators in parallel. This novel soft actuator exhibits potential applications for the multi‐mode actuation of soft robots.

Stick-slip Instability in a Compliant Bistable Double-Slider Mechanism

This paper investigates friction-induced instability in a Single Degree-of-Freedom, pseudo-rigid-body representation of a bistable compliant mechanism composed of two sliders connected with a massless rigid link. The friction force is a function of the state variables through Stribeck effect and variable contact force due to the structural nonlinearity of the mechanism. A Constant normal force ensures the mass-belt contact during oscillation. It is shown that the steady-state response of the vibrating mechanism depends on the belt velocity, applied normal load, and stiffness. The applied normal force and belt velocity, as bifurcation parameters, are used to define the number and location of equilibrium points and their corresponding stability.

Linkage factors optimization of multi-outputs of compliant mechanism using response surface

This paper presents a linkage factors synthesis and multi-level optimization technique for bi-stable compliant mechanism. The linkage synthesis problem is modeled as multiple level factors and responses optimization problem with constraints. The bi-stable compliant mechanism is modeled as a crank slider mechanism using pseudo-rigid-body model (PRBM). The model exerts the large deflection of flexible element which explains compliant mechanism’s bi-stable performance. The design concept is applied on variable input parameters subsets. Though the effect of compliant mechanism process factors on Fmax and PRBM deflection angle (Theta-cap Θ1) are contradictory when studied individually as no response gives best process quality. The relationship model between input factors and responses characteristics were generated by ANOVA and optimized by response surface methodology (RSM). ANOVA shown more significant factors are the initial angle of link1 (θ1) and material thickness (t). The Box-Behnken design of RSM is applied with a desirability function approach to determine the optimum set of parameters for minimizing Fmax and maximizing the Theta-cap (Θ1). Thus, this technique shown flexibility based on the product application could be tested and established.

A hybrid computational method for optimization design of bistable compliant mechanism

Purpose Compliant mechanism has been receiving a great interest in precision engineering. However, analytical methods involving their behavior analysis is still a challenge because there are unclear kinematic behaviors. Especially, design optimization for compliant mechanisms becomes an important task when the problem is more and more complex. Therefore, the purpose of this study is to design a new hybrid computational method. The hybridized method is an integration of statistics, numerical method, computational intelligence and optimization. Design/methodology/approach A tensural bistable compliant mechanism is used to clarify the efficiency of the developed method. A pseudo model of the mechanism is designed and simulations are planned to retrieve the data sets. Main contributions of design variables are analyzed by analysis of variance to initialize several new populations. Next, objective functions are transformed into the desirability, which are inputs of the fuzzy inference system (FIS). The FIS modeling is aimed to initialize a single-combined objective function (SCOF). Subsequently, adaptive neuro-fuzzy inference system is developed to modeling a relation of the main geometrical parameters and the SCOF. Finally, the SCOF is maximized by lightning attachment procedure optimization algorithm to yield a global optimality. Findings The results prove that the present method is better than a combination of fuzzy logic and Taguchi. The present method is also superior to other algorithms by conducting non-parameter tests. The proposed computational method is a usefully systematic method that can be applied to compliant mechanisms with complex structures and multiple-constrained optimization problems. Originality/value The novelty of this work is to make a new approach by combining statistical techniques, numerical method, computational intelligence and metaheuristic algorithm. The feasibility of the method is capable of solving a multi-objective optimization problem for compliant mechanisms with nonlinear complexity.

A multi-response optimal design of bistable compliant mechanism using efficient approach of desirability, fuzzy logic, ANFIS and LAPO algorithm

Compliant mechanisms are promising candidates in precision engineering, soft robotics, space, and bioengineering due to their advantages of free friction, free lubricant, no backlash, monolithic structure, and minimal assembly. However, designing and analyzing of compliant mechanisms are facing the high complexity due to a coupling of kinematic and mechanical behavior in comparison to rigid-body mechanisms. Especially, considering a multi-objective optimization design for compliant mechanisms, the problem is more complicated. Thus, this paper presents a new efficient hybrid methodology for solving the multi-objective optimization design. A hybridization is developed through a combination of finite element method, statistical technique, desirability function approach, fuzzy logic system, adaptive neuro-fuzzy inference system (ANFIS), and Lightning attachment procedure optimization (LAPO). A bistable compliant mechanism is investigated as an application example of the proposed method. First, design variables of the mechanism are determined, and then central composite design is employed to construct a numerically experimental matrix. Though using analysis of variance and Taguchi approach, the design variables are refined to make new populations. Subsequently, desirability values of two performances of the mechanism are computed, and the results are transferred into the fuzzy logic system. The output of fuzzy logic system is considered as single combined objective function. By developing the ANFIS model, the relation between the refined design variables and the output of fuzzy logic system is established. Finally, LAPO algorithm is adopted for solving the multi-objective optimization problem for the mechanism. Three numerical examples are investigated to validate the performance efficiency of the proposed method. The results demonstrate that the proposed method is more efficient than Taguchi-based fuzzy logic. Besides, through Wilcoxon signed rank test and Friedman test, it reveals that the performances of proposed approach are superior to those of the Jaya algorithm and TLBO algorithm. The results of this article can be extended for other complex compliant mechanisms as well as optimization problems with multiple objective functions and more complex constraints.

Friction-Induced Vibration in a Bi-Stable Compliant Mechanism

This paper investigates friction-induced self-excited vibration in a bi-stable compliant mechanism. A single-degree-of-freedom oscillator, hanged vertically, vibrates on a belt moving horizontally with a constant velocity. The oscillator is excited through the frictional input provided by the belt. The friction coefficient is defined as an exponentially decaying function of the sliding velocity. Due to the specific configuration of spring and damper, the normal contact force is variable. Therefore, the friction force is a function of the system states, namely, slider velocity and position. Employing eigenvalue analysis gives an overview of the local stability of the linearized system in the vicinity of each equilibrium point. It is shown that the normal force, spring pre-compression and belt velocity are bifurcation parameters. Since the system is highly nonlinear, a local analysis does not provide enough information about the steady-state response. Therefore, the oscillating system is studied numerically to attain a global qualitative picture of the steady-state response. The possibility of the mass-belt detachment and overshoot are studied. It is shown that one equilibrium point is always dominant. In addition, three main questions, i.e., possible mass-belt separation, location of stick-slip transition and overshoot are answered. It is proven that the occurrence of overshoot is impossible.

Vibration Instability in a Large Motion Bistable Compliant Mechanism Due to Stribeck Friction

The present paper investigates friction-induced self-excited vibration of a bistable compliant mechanism. A pseudo-rigid-body representation of the mechanism is used containing a hardening nonlinear spring and a viscous damper. The mass is suspended from above with the spring-damper combination leading to the addition of geometric nonlinearity in the equation of motion and position- and velocity-dependent normal contact force. Friction input provided by a moving belt in contact with the mass. An exponentially decaying function of sliding velocity describes the friction coefficient and, thereby, incorporates Stribeck effect of friction. Eigenvalue analysis is employed to investigate the local stability of the steady-state fixed points. It is observed that the oscillator experiences pitchfork and Hopf bifurcations. The effects of the spring nonlinearity and precompression, viscous damping, belt velocity, and the applied normal force on the number, position, and stability of the equilibrium points are investigated. Global system behavior is studied by establishing trajectory maps of the system. Critical belt speed is derived analytically and shown to be only the result of Stribeck effect of friction. It is found that one equilibrium point dominates the steady-state response for very low damping and negligible spring nonlinearity. The presence of damping and/or spring nonlinearity tends to diminish this dominance.

Design optimization of segment-reinforced bistable mechanisms exhibiting adjustable snapping behavior

Controlling the nonlinear bistable mechanics is crucial for the development of advanced bistable devices ranging from quantitative mass sensing to smart material/structures. However, for a large amount of pre-shaped bistable mechanisms, one or two specific bistable characteristics such as two switching forces, stroke and bistable index parameter cannot fulfill the special application requirements. Due to the complex coupling effects among different bistable mechanical properties, it is really difficult to modify one specific bistable character without affecting others by just modifying the structure parameters once the bistable configuration and boundary constraints are fixed. With the accurate mechanical analysis of MEMS bistable mechanisms, a novel optimization based method for designing specific bistable characteristic is proposed by modifying the beam local segment’s geometry for optimizing the bistable index parameter and two switching forces respectively. Accordingly, five bistable compliant mechanisms are reconstructed symmetrically or asymmetrically for achieving different bistable mechanics. Also, the sharp change on the nonlinear force- displacement curve induced by the mode switching is analyzed. For experimental study, a quasi-cosine-shaped beam with reinforced local segments is manufactured by hot forming beryllium bronze sheet. The good agreement between the numerical simulation and experimental results validates the effectiveness of the optimization-based bistability design method, thus expanding the potential application range of compliant bistable mechanisms.

Bistable compliant mechanism using magneto active elastomer actuation

One of the challenges in the emerging field of origami engineering is achieving large deformations to enable significant shape transformations. Bistable compliant mechanisms provide a means to achieve this, and the goal of this research is to investigate the feasibility and design of a compliant bistable mechanism that is actuated by magneto active elastomer material. When exposed to an external field, magneto active elastomer material deforms to align embedded magnetic particles with the field. We investigate a case study using magneto active elastomer actuation through the development of finite element analysis models to predict the magnetic field required to snap the device from its first stable position to its second for various geometries and field strengths. The finite element analysis model also predicts the displacement of the mechanism as it moves from one position to the other to determine whether the device is in fact bistable. These results can be used to understand the relationship between the substrate properties and the bistability of the device. The experimental results validate the finite element analysis models and demonstrate the functionality of active magneto active elastomer materials to be used as actuators for such devices and applications of origami engineering.

Mechanism reliability of bistable compliant mechanisms considering degradation and uncertainties: Modeling and evaluation method

The bistable compliant mechanism has been widely used in the field of micro-electromechanical systems, industrial lines, and daily necessities. Enhancing mechanism reliability is helpful to prolong product life and to reduce the maintenance costs of bistable compliant mechanisms. This paper proposes one method to evaluate the mechanism reliability of the bistable compliant mechanism considering degradation and uncertainties of the parameters. The new method can be subdivided as follows: first, the pseudo-rigid body model is used to calculate the motion precision of the mechanism. Second, by introducing the degradation of stiffness and the randomness of the bending line into the kinematic equations, the other equilibrium position can be calculated with respect to the service duration. Third, by using the health index to judge the status of the mechanism, a large sample of failure time is generated and processed by the Kaplan–Meier estimator to characterize the mechanism reliability of the bistable compliant mechanism. A case studied in this paper reveals the mechanism reliability of a typical bistable compliant mechanism under different health indices and provides clues for the reliability evaluation and performance improvement of bistable compliant mechanisms.

Design of a Linear Bistable Compliant Crank–Slider Mechanism

This paper presents a new model for a linear bistable compliant mechanism and design guidelines for its use. The mechanism is based on the crank–slider mechanism. This model takes into account the first mode of buckling and postbuckling behavior of a compliant segment to describe the mechanism's bistable behavior. The kinetic and kinematic equations, derived from the pseudo-rigid-body model (PRBM), were solved numerically and are represented in plots. This representation allows the generation of step-by-step design guidelines. The design parameters consist of maximum desired deflection, material selection, safety factor, compliant segments' widths, maximum force required for actuator selection, and maximum footprint (i.e., the maximum rectangular area that the mechanism can fit inside of and move freely without interfering with other components). Because different applications may have different input requirements, this paper describes two different design approaches with different parameters subsets as inputs. The linear bistable compliant crank–slider mechanism (LBCCSM) can be used in the shape-morphing space-frame (SMSF) as potential application. The frame's initial shape is constructed from a single-layer grid of flexures, rigid links, and LBCCSMs. The grid is bent into the space-frame's initial cylindrical shape, which can morph because of the inclusion of LBCCSMs in its structure.

Modeling and Experimental Validation of Actuating a Bistable Buckled Beam Via Moment Input

Bistable mechanisms have two stable equilibrium positions separated by a higher energy unstable equilibrium position. They are well suited for microswitches, microrelays, and many other macro- and micro-applications. This paper discusses a bistable buckled beam actuated by a moment input. A theoretical model is developed for predicting the necessary input moment. A novel experimental test setup was created for experimental verification of the model. The results show that the theoretical model is able to predict the maximum necessary input moment within 2.53%. This theoretical model provides a guideline to design bistable compliant mechanisms and actuators. It is also a computational tool to size the dimensions of buckled beams for actuating a specific mechanism.

On stability optimization of the deployable bistable compliant structures mounted in the morphing skin: Method and implementation

Morphing skin is the surface of the deployable frame which could reconfigure its shape to present optimal performance in all stages of a task for the re-entry aerospace vehicle. After many years of research effort, design concept and manufacturing methodologies of morphing skin have been developed, especially in the adoption of bistable compliant mechanism (BCM). In order to make morphing skins more stable to accommodate to the air flow and change its profile more accurately, one method on the design and optimization of stability characteristics for deployable BCMs of morphing skin is proposed in this paper. The optimization is developed by the aeroelastic formulation of the deployable BCM mounted on the morphing skin. The optimization problem is considered as a multi-objective-constraint issue and the parametric equations to get the optimal parameters are solved by the immune genetic algorithm. Besides, a case study is proposed to provide evidence that the method can come to the optimal stiffness of BCM, with which the effectiveness about the new method of design and optimization can be testified.

Optimization of retractable structures utilizing bistable compliant mechanism

An optimization approach is presented for a retractable structure consisting of bistable compliant mechanism. The structure is modeled using truss and beam elements, and snapthrough behavior is utilized to generate large deformation under small input displacement and recover the initial shape by application of a small reversal force. The parameters such as nodal locations and cross-sectional areas of members are optimized to minimize the error of nodal displacements from the specified target values. It is shown that the deformed shape, required input force, and stiffness against lateral loads can be controlled independently by modifying nodal locations and stiffnesses of different sets of members. It is also shown through an example of roof model that the maximum load required for shape transformation can be effectively reduced by utilizing the flexibility and self-weight of structure.