Rigid-body Mechanisms Research Articles

Impact of printing parameters on the dynamic outputs of a slider-crank mechanism with FFF-based 3D-printed crank-arms

In this study, the crank-arm of the slider-crank mechanism was produced with different raster angles (45°, 90°, 135°) and infill densities (25%, 50%, 75%, 100%). The effect of these parameters on the dynamics of the slider was investigated experimentally and numerically, and compared with a rigid version of the crank-arm. Firstly, analytical, numerical, and experimental results are obtained for the rigid crank-arm, and the results are compared. Secondly, experiments were carried out on the same experimental setup with 12 crank-arm specimens produced using PLA. Finally, experimental results of sliders were statistically analysed with rigid-body mechanism results, and the flexibility of the crank-arms produced with fused filament fabrication was verified through numerical simulations. As the infill density decreased, the flexibility of the crank-arm increased, and the deviations in the results also grew as the energy change due to the deformation increased. The raster angle had no significant effect on the results except for 25% infill density. However, with 25% infill density, the crank-arm with 90° raster angle followed the rigid crank-arm experimental results best. As a result, it has been observed that the crank-arm produced with different printing parameters has a significant effect on the dynamics of the slider.

Novel Soft Gripper With Adjustable Performance Based on Blade Flexures

Abstract The design of soft grippers is challenging as the target objects to be handled involve a wide variety of sizes, shapes, and softness. Most grippers reported present drawbacks, e.g., complex control strategies for stiffness and force variation, inadequate adaptability to target shape variability, and complicated adaptation to manipulators, which in turn limit their implementation in applications such as harvesting. This paper presents a novel overlay soft gripper based on an assembling mechanism and passive soft structures, enabling the modification of grip size, orientation, and gripping force. This gripper can be assembled over a commercial robot-gripper taking the closing motion of this as the input to perform its closing motion. Input and output parameters are related by means of the displacement transmission mechanism which converts the closing motion of the robot-gripper into the closing motion of the overlay soft gripper. The gripping force can be modified through the change of stiffness, via adjustment of effective length using contact elements, of internal blade flexures. The displacement transmission mechanism works in two modes: as rigid-body mechanism without the contact elements and as rigid-body/flexible mechanism with the contact elements. The relationships between input and output parameters are obtained analytically for the case of rigid-body mechanism, and through finite element analysis simulations for the case of rigid-body/flexible mechanism. Relationships between input and output parameters are approximated with polynomial surfaces. Finally, physical prototypes are manufactured and assembled on their respective robot-grippers to qualitatively demonstrate their performance.

The principal bundle structure of continuum mechanics

In this paper it is shown that the structure of the configuration space of any continua is what is called in differential geometry a principle bundle. A principal bundle is a structure in which all points of the manifold (each configuration in this case) can be naturally projected to a manifold called the base manifold, which in our case represents pure deformations. All configurations projecting to the same point on the base manifold (same deformation) are called fibers. In this paper, it is shown that each of these fibers is then naturally isomorphic to the Lie group SE(3) representing pure rigid body motions. Furthermore, it will be shown that it is possible to define intrinsically (coordinate free), what is called a connection and this allows to split any continua motion in a rigid body sub-motion and a deformable one in a completely coordinate free way. As a consequence of that it is then possible to properly define a pure deformation space on which an elastic energy can be defined and this will be related to other literature on intrinsic strain which has not shown the geometric structure which will be presented in this work. This will be shown using screw theory and Lie groups. Screw theory is vastly used in the analysis of rigid body mechanisms but is not normally used to analyse continua. The paper will also relate known concepts of continua like helicity and enstrophy to screw theory concepts which will become evident by the presented construction.

3D printer-driven design of a non-assembly titanium surgical instrument using compliant lattice flexures

Metal additive manufacturing is a promising technology for the production of functional medical products, due to its high shape complexity and resolution, and ability to withstand sterilization temperatures. This study explores the possibility of designing a completely non-assembly steerable surgical instrument using Selective Laser Melting. Despite its advantages for medical devices, the rough surface quality of unfinished parts can be problematic for non-assembly designs, leading to increased friction and wear in rigid body mechanisms and tendon-actuated mechanisms. We investigated printing of rolling contact joints with crossed flexures as low-friction joints, adjusted for printing in titanium for the design of the instrument. Grid-based lattice structures were incorporated as miniature flexures, and we explored the influence of various grid sizes on the flexibility and bending stiffness of the lattices. Based on this exploration, we altered the rolling joint configuration from two crossed flexures to a single straight flexure for our design. The resulting steerable surgical instrument design is completely non-assembly, including its actuation, facilitates easy removal of support structures, and requires no surface finishing steps. It has a diameter of less than 20 mm, facilitates opening and closing of a grasper, and steering of the grasper by 20 degrees.

Emerging Technologies in Displacement Amplification of Lever and Bridge-Type Compliant Mechanism: A Review Article

This review article provides a survey of emerging technologies in displacement amplification of lever-type and bridge-type compliant mechanisms. The displacement amplification is possible with a compliant mechanism. The compliant mechanism is beneficial and efficient because of simplicity in the design and where there is accuracy, compactness, and precision is needed. We can use various categories of displacement amplification of the compliant mechanism depending upon the application. In recent years, displacement amplification of compliant mechanisms gain more attention to the researchers due to the superiority of the mechanical compliant mechanism is compared with a rigid-body mechanism. Displacement amplification compliant mechanism such as bridge types, lever type, a micro-Leverage Mechanism has briefly discussed. The performance parameters such as the principle of working, types of displacement compliant mechanism, fabrication process, operating frequency and displacement amplification ratio are found out

Design of a variable-diameter wheel with a novel distributed compliant mechanism

Compliant variable-diameter mechanisms enable adaptation of variable-diameter wheels to both road and soft terrain. Conventional compliant variable-diameter mechanisms, in which every wheel-foot is an independent load-bearing structure, rely heavily on rigid-body mechanisms. To overcome the structure restriction and improve their performances, we introduce a novel compliant mechanism in which circumferentially distributed leaf springs or combination springs with large deformation range are used as flexible components. The springs constitute the closed outer ring and the overall load-bearing structure in the wheel. A novel screw transmission mechanism was designed to achieve motions with two degrees of freedom. Based on the geometric relationships, a dimensional design method for the mechanism is proposed. The chained beam-constraint-model and integration methods are introduced to obtain the spring deflections and maximum hub rotation angle. These methods can be used for further design of the transmission mechanism. The wheel design is then verified experimentally. The results indicate that the required design targets were achieved. Thus, the proposed mechanism diversifies the structure type and design of compliant mechanisms and expands the applicability of variable-diameter wheels in mobile platforms.

Compliant mechanisms for dust mitigation in Lunar hardware development: technology and material considerations

During the Apollo missions, astronauts observed negative impact of Lunar dust on the surface hardware. The characteristics of Lunar environment and the regolith properties accelerate the contamination and promote the abrasion and clogging of different components in the equipment. To protect the hardware from damages in the future Lunar missions, several mitigation technologies must be adapted. In this work, we propose to consider application of solutions that are naturally dust resilient. Such solutions, called implicit dust mitigation technologies, include usage of compliant mechanisms. Compliant mechanisms use elastic deformation to achieve motion and can replace rigid-body mechanisms that suffer increased friction and jamming due to dust accumulation in the inter-element gaps. Material selection for compliant mechanisms needs to be considered very early in the design process, and as demonstrated in our work, it is crucial to the final mechanism performance.

Surgical Microgrippers: A Survey and Analysis

Abstract This review article provides an overview of some challenges that arise when developing new medical robotic microgrippers. The main challenges are due to miniaturization and are present in the manufacturing and assembly processes, the types of mechanisms, the biomaterials used, the actuation principles, and the compliance with some standards and regulations. The main medical fields where these microgrippers are used are in minimally invasive surgery (MIS) and biomedical applications. Therefore, taking these two large groups into account, this review presents a microgrippers classification according to the type of mechanism used (traditional rigid-body mechanisms and complaint mechanisms). Moreover, parameters such as applications, functionalities, degrees-of-freedom (DOF), sizes, range of motion, biomaterial used, and proposed methods are highlighted. The analysis of 27 microgrippers among commercial and developed by research institutes is presented.

Stiffness Modeling and Deformation Analysis of Parallel Manipulators Based on the Principal Axes Decomposition of Compliance Matrices

Abstract This paper presents a general equivalent approach to solve the stiffness modeling or load-deformation problem of non-redundant parallel mechanisms. Based on the principal axes decomposition of structure compliance matrices, an equivalent six-degrees-of-freedom (6-DOFs) serial mechanism is established to approximate the load-deformation behavior of each flexible link in the mechanism. Hence, each limb of the parallel mechanism can be equivalent to a serial redundant rigid body mechanism with passive elastic joints, and the load-deformation problem can be transformed to the equilibrium configuration calculation of the equivalent mechanism. The main advantage of the proposed method is that the robotic kinematics and statics, rather than the elastic mechanics, can be directly adopted to solve the equilibrium configuration of the parallel mechanism under external load. Besides, a closed form solution of the corresponding deformation can be obtained, which can be solved by the gradient-based searching algorithm. Therefore, the final deformation will no longer be linear to the external load, which makes this method more accurate and more suitable for the deformation prediction and compensation in real industrial working conditions. In order to verify the effectiveness and correctness of this method, a 3PRRU parallel manipulator will be introduced as an example, to compare the load-deformation results with the finite element analysis (FEA) simulation and matrix calculation methods, so the nonlinearity feature can be shown in an intuitive manner.

Dimensional synthesis of a spherical linkage crank slider mechanism for motion generation using an optimization algorithm

Abstract. In the present study, Fourier theory is applied to establish the expression of rigid-body poses of a spherical four-bar crank slider rigid-body guidance mechanism. According to an analysis of the harmonic components of the trajectory curve and rigid-body rotation angle, it has a certain relationship with the geometric parameters of the mechanism. On this basis, the rigid-body poses are normalized by preprocessing. Then, the rotation angle of the curve around the y axis and z axis is determined, respectively. The theoretical formulas used for calculating the real sizes and the installation position parameters of the desired spherical four-bar crank slider rigid-body guidance mechanism are established. Besides this, a genetic optimization algorithm and theoretical formulas are applied to solve the dimensional synthesis of motion generation for the spherical four-bar crank slider mechanism. The effectiveness of the proposed method is illustrated by an example. The maximum Euclidean distance error of the rigid-body position of the results with the highest similarity is 0.0086, and the average Euclidean distance error is 0.0044. The maximum error of the rigid-body orientation is 0.0179, and the average error is 0.0065.

Modeling and identification of rate-dependent and asymmetric hysteresis of soft bending pneumatic actuator based on evolutionary firefly algorithm

Soft-bending pneumatic actuators (SBPA) have shown great potential in various applications owing to their intrinsic compliance. However, motion control is still challenging because of the complicated hysteresis of the elastic material and pneumatic system, which unlike the general hysteresis found in the rigid body mechanism, is rate-dependent and asymmetric. A precise hysteresis model is crucial for improving the performance of SBPA. This study proposed a rate-dependent modified generalized Prandtl–Ishlinskii (RMGPI) model for a vulcanized silicone rubber-based fast pneu-net soft bending pneumatic actuator (fp-SBPA) to describe complicated hysteresis characteristics. A visual feedback system obtained the bending angle in real time. With the increase in the number of operators, the identification of the proposed model parameters became more complicated and time-consuming; thus, an evolutionary firefly algorithm (EFA) was developed to improve identification efficiency. A series of experiments and comparison studies were conducted to verify the effectiveness of the proposed model and identification method.

Freeform Auxetic Mechanisms Based on Corner-Connected Tiles

Auxetic mechanisms based on corner-connected polygonal tiles have been used to design deployable structures and are currently applied to programmable surfaces. However, existing surface structures are realized by compliant kirigami, and the realization with rigid-body mechanism, in particular with thick panels, is still limited to configurations with global symmetries due to the mechanism's overconstraining nature. In this study, we generalize the auxetic mechanisms into freeform surfaces by imposing local symmetries on polyhedral surfaces. From the discussion of kinematics, we show that polyhedral surfaces whose edges coincide with a Voronoi diagram of points on the surface can be converted to kinematics systems of corner-connected kinematic tiles. We propose hard constraints to ensure the Voronoi property required for the kinematics and soft constraints to attain a large expansion ratio. Then, we provide an optimization-based scheme using the proposed constraints to achieve a mechanism from a given target surface. We also propose methods for accommodating the thickness of the tiles and show different variations of joints. As a result, we obtained deployable surfaces of positive and negative Gaussian curvature that can deploy and contract with a one-DOF mechanism. If the structure is viewed as a cellular material, it has an auxetic property with Poisson's ratio of -1. It is also potentially scalable to architectural applications because our mechanism is composed of rigid bodies and hinges.

Stability analysis of Mars soft landing under uncertain landing conditions and two landing strategies

PurposeThe purpose of this paper is to study the landing performance of the Mars lander considering uncertain landing conditions under two landing modes.Design/methodology/approachA dynamics analysis model for the legged Mars lander is established for landing simulation, where the nonlinear large-deformation flexible buffer rods are equivalently modeled with a rigid-body mechanism with external forces and movement limit. Sensitivities of the landing stability to various landing conditions are analyzed using the Quasi–Monte-Carlo-based Sobol’ method and computer-aided landing simulations. Moreover, based on the results of sensitivity analysis, sensitive parameters are selected for estimating the safe boundaries for stability indices of rotation and clearance.FindingsIt can be concluded from this study that the lander has excellent ability against overturning. The shutdown-before-touchdown strategy helps to maintain than landing pose, and the shutdown-at-touchdown strategy helps to prevent the nozzle from colliding with the surface of Mars.Practical implicationsThis study provides a theoretical reference to choose the better landing strategies for Mars landers considering uncertain landing conditions.Originality/valueA parameterized dynamics Mars lander model and a simplification method are proposed to simulate the landing on Mars. Uncertain landing conditions are parameterized and considered in the dynamics model. Sensitivity analysis and safe boundary methods are used to compare the landing performances with two landing strategies.

Seismic performance of a structural concrete pile-wharf connection before and after retrofit

A full-scale precast prestressed concrete (PC) pile-wharf specimen with a T-headed dowel bar connection detail was tested under realistic loading and boundary conditions. The testing program introduced several seismic loading protocols, which were determined from nonlinear dynamic analyses of a typical U.S. port structure subjected to ground motions for various hazard levels. Conventional reversed cyclic loading tests were also conducted on the pile-wharf connection, damaged by seismic loading protocols, before and after retrofit. The specimen showed excellent seismic performance in terms of both strength and ductility. It was confirmed that the lateral drift response of such a PC pile-wharf connection is largely governed by a rigid-body rocking mechanism, with spalling in the pile and deck near the joint region appearing to be a main cause of stiffness degradation. This study also considered a section enlargement technique as an efficient retrofitting method of pile-wharf connections in container port structures. The retrofitted pile-wharf connection (with prior seismic damage) showed higher stiffness and improved capacity, but its deformation capacity (ductility) was inevitably limited by previously accumulated damage along the precast pile (where no strengthening was applied).

Insight into numerical solutions of static large deflection of general planar beams for Compliant Mechanisms

Compliant Mechanisms (CMs) have been a hot research spot in recent years due to their distinguished mechanism concept from conventional rigid-body mechanisms: CMs can transfer motion, force, and energy only through the deflection of flexible components. Therefore, the accurate and efficient kinetostatic modeling for these elementary flexible components plays a rather important role regarding conducting synthesis of a studied compliant mechanism. In this paper, we have reviewed the commonly-used beam modeling methods in CMs, most of which are essentially dedicated to handling geometrically nonlinear Euler–Bernoulli beam theory. Mathematically speaking, this beam model is essentially a boundary value problem (BVP) of an ordinary differential equation (ODE). We then introduced certain commonly used numerical methods for BVPs to solve the problem where straight beams and circular initially curved beams (ICBs) are studied as two example cases. We have also demonstrated the detailed derivation of these methods and the numerical results along with the corresponding insights on them as well. Besides, we have modeled 2 representative revolute mechanisms (straight-beam-based cross-axis compliant revolute joint and circular-beam-based compliant revolute joint) to prove the feasibility of synthesizing CMs using these numerical methods. Error analysis is presented thereafter, which also confirms the effectiveness of these numerical methods.

Actuator Fluid Control Using Fuzzy Feedback for Soft Robotics Activities

Soft robotics is a new field that uses actuators that are non-standard and compatible materials. Industrial robotics is high-throughput manufacturing devices that are quick and accurate. They are built on rigid-body mechanisms. The advancement of robotic production now depends on the inclusion of staff in manufacturing processes, allowing for the completion of activities that need cognitive abilities that are now beyond the scope of artificial networks. Hydrostatic pressure is used to achieve high deflections of structures that are based on the elastomeric in Fluid Actuators (FAs). Soft actuators based on the fluid are a popular choice safe for humans and lightweight robots. However, owing to a deficiency of durable, accurate, and affordable sensors that can be combined with actuator systems that are highly deformable and that use low-cost materials and production, closed-loop management of such actuators remains difficult. Such actuators, in combination with hydrodynamic force feedback, form a series-elastic actuation (SEA), which eliminates virtually friction from all driving-point. Fuzzy control is a smart computing analysis technique that enables complex systems to be controlled independently of a mathematical model. Fuzzy logic is used to optimize the parameters of a Fuzzy Logic Controller (FLC’s) function to find the best rational controller for an automated robot. Because discontinuous endpoint friction is undetectable to the pressure of the fluid internally, feedback from traditional external force using force/tactile sensing is preferred. As a result, a fuzzy-based control using linear feedback was developed and used to test the integrated system’s response dynamically and location accuracy.

Design, simulation and testing of an isotropic compliant mechanism

In this paper, the concept of isotropic compliance is extended to the field of compliant mechanisms. Starting from the design of a rigid-body mechanism, a planar compliant system is determined by applying the rigid-body replacement method. The static behaviour of the isotropic compliant mechanism is validated by finite element simulations and experimental tests. The extension of the proposed method to the Euclidean Space E(3) is discussed.

Applications of compliant mechanism in today’s world – A review

In the world of globalization & competitive market there is demand of alternative designs with improved quality, economy & safety. Emerging designs of compliant mechanisms making noticeable contribution to economize cost of production. Compliant mechanism derives their mobility through deflection of flexible members opposite to the conventional rigid body mechanism. The integration of functions into fewer parts, compliant mechanisms offer significant advantages such as fewer parts, less wear, noise & backlash. Researchers expects this field will grow enormously due to advances in the compliant mechanism theory, development of materials with superior quality & advancement in 3D printing technology in the recent years. Recently many familiar examples of compliant mechanism are used in transportation, aerospace, micro-mechanism, biomedical, hand held tools, MEMS & robotics industry. The objective of the current work is to study compliant mechanisms & their applications in various fields communicated by various researchers.

Efficient spatial compliance analysis of general initially curved beams for mechanism synthesis and optimization

Compliant Mechanisms (CMs) present several desired properties for mechanical designs. Conventional rigid-body mechanisms composed of rigid links connected at kinematic joints, serve as devices to transfer motion, force and energy by the movements of rigid links whereas CMs are able to present the same function only through deflection of flexible members. Most designs of CMs in the current literature employ straight beams as the elementary flexible members whereas initially curved beams (ICBs) also provide potential advantages for CMs such as large range of motion and small strain range. This paper presents an efficient spatial compliance analysis method of general ICBs. The spatial compliance analysis of different types of ICBs (such as varying-curvature beams and varying-cross-section beams) was conducted, followed by Finite Element Analysis (FEA) verification. Next, the modeling and optimization of two types of CMs including ICB-based parallelogram mechanisms and ICB-based Ortho-planar springs were carried out by applying screw theory under the framework of position space concept and parameter normalization strategy where a class of anti-buckling translational parallelograms with high load-bearing capacity and a type of compact 2R1T (2 rotational DOF and 1 translational DOF) compliant kinematic joints were obtained. The corresponding FEA was conducted to verify the optimal results.

Geometric synthesis method of compliant mechanism based on similarity transformation of pole maps

Abstract. This paper presents a geometric synthesis method for compliant mechanisms based on similarity transformation of pole maps. Motion generation is a typical and common mechanism synthesis task, so this study takes it as the design requirement to expound the proposed method. Most of the current research work relies on numerical solution of the nonlinear Bernoulli–Euler beam model, numerical simulations or physical experiments to study the synthesis method of compliant mechanisms. There is a lack of simpler and more efficient methods to achieve motion generation of compliant mechanisms with various topologies. This study is based on pole map which is a geometric tool to describe the motion of rigid-body mechanisms. In this paper, we first demonstrate the feasibility of applying the similarity transformation of pole map to compliant mechanisms. It is proved that the pole map of compliant mechanisms has the same characteristic as rigid-body mechanisms during similarity transformation. Then we present the procedure of synthesis method in detail and expound the establishment method of function module which can avoid the functional defects of the final designed mechanism. At last, we take the compliant geared linkages and compliant four-bar linkage as examples to illustrate the novel synthesis approach. The result is an applicable and effective synthesis method for motion generation of compliant mechanisms.