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This paper proposes the design of a wholly mechanical constant-force gripper that can accommodate the imprecise manipulation of brittle/delicate objects by the actuation. This was achieved by designing a constant-force mechanism as the jaw that allowed a constant force to be applied to the grasping objects regardless of the displacement of the mechanism. The constant-force mechanism is attached to the end effector of the gripper via a parallelogram mechanism which ensures that the jaws remain in parallel. The constant-force mechanism combines the negative stiffness of a bistable mechanism and the positive stiffness of a linear spring to generate a constant force output. By preloading the positive stiffness mechanism, the magnitude of the constant force can be adjusted to be as low as zero. The constant-force mechanism has been fully modelled and simulated using finite element analysis. A normalised force-displacement curve has been developed that allows to obtain the simplified analytical negative stiffness of the bistable mechanism. The design formulation to find the optimal configuration that produces the most constant force has been developed. Illustrated experiments prove the concept of the design although the discrepancies between finite element analysis results and testing results exist due to bistable beam manufacturing error. [ABSTRACT FROM AUTHOR]

The initial version of this paper was presented at 2014 Workshop on Fundamental Issues and Future Research Directions for Parallel Mechanisms and Manipulators, Tianjin, China.The conceptual design of three types of decoupled, compact, and monolithic XYZ compliant parallel manipulators (CPMs) is taken into account in this paper using the position space concept. The CPMs are termed CUBEs due to the shape of their compact structures. The position space of a compliant module is the combination of all permitted positions in an XYZ CPM system where the constraint of this compliant module in the XYZ CPM system remains unchanged when the position of the compliant module changes within the position space. The position of each compliant P joint is considered relative to its adjacent compliant joint/module rather than being considered in insolation. A design method for obtaining monolithic XYZ CPMs is proposed in terms of both the kinematic substitution and position spaces. Three types of monolithic XYZ CPMs are then demonstrated using the proposed method, with the help of three classes of kinematically decoupled three degrees of freedom translational parallel mechanisms. These monolithic XYZ CPMs include a 3-PPP (P: prismatic) XYZ CPM, a 3-PPPR (R: revolute) XYZ CPM, and a 3-PPPRR XYZ CPM. The position space concept can enable the system configurations to be designed based on the chosen optimization requirements, which include considerations such as compactness or minimization of parasitic rotations. This provides an efficient and systematic method to arrange the relative position between any two compliant joints/modules so that one can easily generate practical and useful configurations for XYZ CPMs. The resulting XYZ CPM is the most compact one when the fixed ends of the three actuated compliant P joints thereof overlap or are as close to each other as possible. [ABSTRACT FROM AUTHOR]

This paper deals with the design of 3-legged distributed-compliance XYZ compliant parallel manipulators (CPMs) with minimised parasitic rotations, based on the kinematically decoupled 3-PPPRR (P: prismatic joint, and R: revolute joint) and 3-PPPR translational parallel mechanisms (TPMs). The designs are firstly proposed using the kinematic substitution approach, with the help of the stiffness center (SC) overlapping based approach. This is done by an appropriate embedded arrangement so that all of the SCs associated with the passive compliant modules overlap at the point where all of the input forces applied at the input stages intersect. Kinematostatic modelling and characteristic analysis are then carried out for the proposed large-range 3-PPPRR XYZ CPM with overlapping SCs. The results from finite element analysis (FEA) are compared to the characteristics found for the developed analytical models, as are experimental testing results (primary motion) from the prototyped 3-PPPRR XYZ CPM with overlapping SCs. Finally, issues on large-range motion and dynamics of such designs are discussed, as are possible improvements of the actuated compliant P joint. It is shown that the potential merits of the designs presented here include a) minimised parasitic rotations by only using three identical compliant legs; b) compact configurations and small size due to the use of embedded designs; c) approximately kinematostatically decoupled designs capable of easy controls; and d) monolithic fabrication for each leg using existing planar manufacturing technologies such as electric discharge machining (EDM). [ABSTRACT FROM AUTHOR]

This paper proposes conceptual designs of multi-degree(s) of freedom (DOF) compliant parallel manipulators (CPMs) including 3-DOF translational CPMs and 6-DOF CPMs using a building block based pseudo-rigid-body-model (PRBM) approach. The proposed multi-DOF CPMs are composed of wire-beam based compliant mechanisms (WBBCMs) as distributed-compliance compliant building blocks (CBBs). Firstly, a comprehensive literature review for the design approaches of compliant mechanisms is conducted, and a building block based PRBM is then presented, which replaces the traditional kinematic sub-chain with an appropriate multi-DOF CBB. In order to obtain the decoupled 3-DOF translational CPMs (XYZ CPMs), two classes of kinematically decoupled 3-PPPR (P: prismatic joint, R: revolute joint) translational parallel mechanisms (TPMs) and 3-PPPRR TPMs are identified based on the type synthesis of rigid-body parallel mechanisms, and WBBCMs as the associated CBBs are further designed. Via replacing the traditional actuated P joint and the traditional passive PPR/PPRR sub-chain in each leg of the 3-DOF TPM with the counterpart CBBs (i.e. WBBCMs), a number of decoupled XYZ CPMs are obtained by appropriate arrangements. In order to obtain the decoupled 6-DOF CPMs, an orthogonally-arranged decoupled 6-PSS (S: spherical joint) parallel mechanism is first identified, and then two example 6-DOF CPMs are proposed by the building block based PRBM method. It is shown that, among these designs, two types of monolithic XYZ CPM designs with extended life have been presented. [ABSTRACT FROM PUBLISHER]

In a micro-manipulation system, the compliant gripper is used for gripping, handling and assembling of objects. Large displacement and anti-buckling characteristics are desired in the design of the gripper. In this paper, a compliant gripper with these two characteristics is proposed, modelled and verified. The large displacement is enabled by using distributed compliance in a double-slider kinematic mechanism. An inverted flexure arrangement enables the anti-buckling of the gripper when closing the two jaws. A pseudo-rigid-body model (PRBM) method with the help of virtual work principle is employed to obtain several desired analytical relations including the amplification coefficient and kinetostatics. The results of the finite element analysis (FEA) are shown to be consistent with the results of the derived analytical model. An experimental test was carried out through a milling machined aluminium alloy prototype, the results of which verify the good performance of the compliant gripper. [ABSTRACT FROM AUTHOR]

Output accuracy performance is directly determined by geometric errors and working poses of a mechanism. Accuracy sensitivity as geometric error transmission coefficient, closely relates to pose configuration and geometric parameters. This research focuses on accuracy of a 3-RPR planar parallel mechanism: firstly, established 3 models in an analytic form, to describe relationship between output errors and geometric ones, then they are mutually verified statistically. Secondly, the anisotropy and periodic fluctuation of position errors, independently contributed by each category of geometric errors, are illustrated; and mirror symmetric trajectories and poses generating output errors with mirror symmetry, are also revealed by numerical simulation. Finally, the radical accuracy model in an analytic form, was established through variance and covariance analysis on output errors. We concluded that the radical error of the movable platform in central symmetric poses, follows Rayleigh distribution pattern. Through statistical comparison with Monte Carlo simulation, the radical error model was demonstrated, that provided a reference for accuracy design for other planar parallel mechanism. [ABSTRACT FROM AUTHOR]

Objective: This work presents the results of Benchtop tests and pre-clinical study of a novel design for a foldable magnetic anastomosis device. The device can be deployed through an endoscope device channel and fold into a ring larger than the deployment port. This new design enables the target application in JJ-anastomosis creation. Material and methods: The folding anastomosis device is constructed from a chain of permanent magnets suspended in a suture weaving inspired by the contact-aided compliant mechanisms. The device was deployed through an endoscope in Benchtop experiments and its expected coupling force was measured in a pull test. A set of experiments was executed during the pre-clinical study, where the device was deployed in the abdomen, to estimate the reliability of deployment and the plausibility of the use in jejuno-jejunal (JJ)- and gastrojejunal (GJ)-anastomosis creation. Results: The presented folding anastomosis device was shown to deploy through an endoscope device channel and a catheter with an inner diameter of 3.2 mm. After deployment the device folds reliably into a ring with an outer diameter of 7–8 mm. The folded device was shown to exhibit a coupling force comparable to similar cases of JJ-anastomosis creation. It is concluded that the presented design of a folding magnetic ring is suitable for select cases of magnetic compression anastomosis where the device is either delivered through a catheter to fold into an anastomosis ring larger than the deployment port or through an endoscopes device channel to allow for convenient visual confirmation of the device during placement. [ABSTRACT FROM AUTHOR]

• A Cross-Axis Pivot incorporating variable section beams is presented. • A routine to generate the BCM coefficients with various beam shapes is reported. • A Bi-BCM model is developed to analyze the pivot under different load scenarios. • Finite Element Analysis is used to verify the model accuracy. • Experiments are performed on physical prototypes to further validate the results. [Display omitted] The Cross-Axis Flexural Pivot (CAFP) is a well-established compliant rotational joint characterized by a highly configurable behavior. Its classic form, consisting of two uniform beams that cross at an arbitrary angle, has been thoroughly examined via either theoretical approaches or Finite Element Analysis (FEA). Conversely, the effects of utilizing variable section beams have had minor consideration, possibly due to the more complex modeling phase. The present paper addresses the analysis of CAFPs incorporating beams whose width and thickness are assumed to vary along the axis with either linear or parabolic functions. The CAFP planar behavior is studied resorting to the Beam-Constraint Model (BCM) for different load cases, namely with an ideal rotation applied to one rigid link or a more practicable cable-driven actuation. To extend the use of BCM to large deflections, each CAFP's beam is modeled as a chain of two BCM elements, named Bi-BCM. A preliminary study has been carried out to establish empirical equations that provide the BCM characteristic coefficients for every considered beam shape. Next, these have been used to perform the pivot behavioral analysis and to generate, as an output of the sensitivity studies, the performance maps of stiffness, maximum stress and center shift. These results have been verified with FEA, which confirmed the Bi-BCM accuracy for any tested configuration. Finally, direct comparisons between predicted behaviors of the CAFP actuated via the flexible cable and experimental data obtained with 3D printed specimens further validated the proposed Bi-BCM model. [ABSTRACT FROM AUTHOR]

• We proposed an efficient compliance analysis method of initially curved beams. • We validated the method using Finite Element Analysis. • We conducted compliance analysis and optimization of ICB-based mechanisms. • We used weighted-sum method and genetic algorithm for the optimization process. 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. [ABSTRACT FROM AUTHOR]

To avoid the effects of the overlap phenomenon among powder particles, the concept of an effective particle number was introduced, and multi-parameter analytical models for laser powder-fed additive manufacturing (LPF-AM) cladding geometric characteristics were established based on the laws of energy and mass conservation. Experimental research on the LPF-AM of a FeCr alloy was carried out, and the theoretical results are discussed and compared with the experimental data from the perspective of the laser energy density and powder density. The results showed that the cladding area was proportional to both the laser energy density and powder density. The mixing area and dilution rate decreased gradually with increasing powder density, while they increased first and then decreased with increasing laser energy density. The analytical model calculation values fit well with the experimental measurements. The microstructure of the cladding layer and substrate showed good metallurgical bonding, and the micro-hardness variation from the mixing to the cladding zone ranged from 423 to 627 HV. [ABSTRACT FROM AUTHOR]

Membranes have been widely applied in spacecrafts, such as solar sails and deployable antenna structures, due to their light weight and high compact ratio. The geometric profile of deployed membranes has an important impact on the performance of a membrane-based spacecraft, which should be accurately predicted during the deployment process. However, some observable dynamic deployment characteristics of membranes are difficult to be simulated accurately. In this paper, an equivalent torsion spring model for the membrane crease is proposed and derived to accurately describe the complex deployment process of the membrane. The elastic and plastic phases of the equivalent spring are both considered and derived in this model. Based on this method, the experimentally-observed spring-back position and the corresponding torque of the membrane can be quantitatively predicted. Combining the equivalent torsion spring model with the finite element software, the deployment processes of a single-fold and a Miura-fold are simulated and compared with the experimental results, showing a good agreement. Finally, the deployment process of a 3-axis stabilized solar sail is simulated using this method. [Display omitted] • Proposition of an innovative crease equivalent torsion spring model. • Comparison and optimization of parameters based on crease experiments. • A variety of numerical examples with single/Miura-ori fold. • Simulation of the deployment for a Z-type folding triangle membrane. • Accurate model-based prediction of crease stress and spring-back. [ABSTRACT FROM AUTHOR]

Highlights • We present two accuracy models for the L/R mechanism to analyze the mechanism output errors. • We investigate the lead screw errors of the mechanism from the transmission train with DOE. • Two accuracy models for the L/R mechanism are verified through DOE with MC simulation, with their relations applied in accuracy analysis. • The statistical model for non-synchronous error of the mechanism reveals the orientation errors prevail other errors. Abstract With development of Chinese space science and technology, plenty of microgravity experiments will be conducted in the Chinese Space Station to be built, and therefore demand for high-precision electromechanical equipment increases substantially. In this paper, a comprehensive accuracy analysis of a new type of auto lock-or-release (L/R) mechanism, which is applied in the Space Station Microgravity Platform (SSMP), is implemented. Firstly, two models (vector analysis model and vector differential model) are, therefore, proposed to analyze output errors of the mechanism. Due to transmission errors from the transmission chain of the gear mechanism, influence factors on axial errors of lead screws are analyzed using design of experiment (DOE) for factor sensitivities. It shows that manufacturing tolerances of the lead screw is the dominant factor. Then, verification of the two proposed accuracy models is comparatively implemented through Monte Carlo (MC) simulation and DOE. Using the present accuracy model, location errors of the lead screw throughout the mechanism's working stroke are illustrated, where the non-synchronous error of the mechanism is particularly discussed. A linear relation between the variance of the non-synchronous error and that of the structural error is established, followed by analyzing influence factors on the non-synchronous error. [ABSTRACT FROM AUTHOR]

• A constraint flow concept and its mathematical expressions are introduced. • A constraint-flow based method to the synthesis of decoupled XYθ-CPMs is proposed. • One decoupled XYθ-CPM is designed, analytically modelled and experimentally tested. It is an open challenge to synthesize XYθ compliant parallel mechanisms (CPMs) with decoupled motion and actuation characteristics for increasing applications from semiconductor manufacture to bio-nanotechnology. The key issue in the synthesis is to obtain the permitted constraints of the constituent compliant modules. In this paper, a constraint-flow based method is proposed to address this need, and up to 6859 constraint combinations are derived for the compliant modules, leading to a great number of possible synthesis schemes. Two case studies of schemes are presented to demonstrate the proposed synthesis method. One of the designs is analytically modelled, with less than 6.45% difference compared with the FEA results. A prototype of the design is also fabricated and experimentally tested. The analytical, FEA and/or experimental results show that the couplings are less than 3.9%, the translation resolution is 5 nm, and the rotation resolution is 50 nrad. The introduced constraint flow concept is not limited to the application of synthesizing decoupled XYθ CPMs, but also is an alternative and effective method in synthesizing other types of CPMs. [ABSTRACT FROM AUTHOR]

• We proposed a new compliant amplification mechanism for piezoelectric actuators. • Kinetostatic models of the mechanism are derived and compared with FEA. • An optimization design is obtained based on the analytical models. • We designed an experimental hardware to test the fabricated prototype. This paper proposes a new compliant mechanism for the stroke amplification of piezoelectric actuators. Compared with the existing ones, this compliant stroke amplification mechanism (CSAM) has several advantages including lightweight, less stress concentration, large motion range, as well as ease of manufacture in macro- and micro-scales, mainly due to the completely distributed compliance and largely reduced moving mass. Kinetostatic models of the CSAM, with consideration of the payloads applied on the output stage, are derived for quick and insightful determinate analysis, which enables optimization of the associated parameters to achieve different objectives. The results obtained from the kinetostatic models are in reasonable agreement with the FEA simulation results, with less than 3.8% difference when the input displacement is less than 10 µm. An optimization method, based on the analytical models, is introduced and employed to increase the amplification ratio of the CSAM by up to 240%. The optimized CSAM is an excellent candidate for the stroke amplification of piezoelectric actuators, which is fabricated and experimentally tested. The optimization method is able to be extended to design other compliant mechanisms with optimized size, shape and topology configuration simultaneously. [ABSTRACT FROM AUTHOR]

• Statistical prediction models of multi-layer cladding structures were established. • Effects of process parameters on geometric characteristics were revealed. • An optimized model of multi-layer cladding structures was established. • The optimal process parameters combination of multi-layer cladding was obtained. In the laser Directed Energy Deposition (DED) manufacturing of parts, severe deformation caused by the uneven geometric characteristics of a multi-layer deposition fusion area occurs extremely easily due to the complexity and insufficient understanding of the process. The above results in a significant decline in the overall geometric quality of the parts. To study the influence of the laser DED process parameters on the geometric characteristics of multi-layer cladding, a response surface method was used to carry out an experimental study of the multi-layer cladding structures. Statistical prediction models of multi-layer cladding manufacturing were established among the laser power, scanning speed, powder feeding rate, lap ratio and cladding width, cladding zone area, fusion zone area, and flatness ratio. The accuracy, adaptability and relevance of the models were verified. The influence of each process parameter on the geometric characteristics of the multi-layer cladding structure was analysed, and the laser DED process parameters were optimized. Experimental results show that the surface forming quality of specimens processed with optimized process parameters is good. Relative errors between the experimental and predicted values of the geometric characteristics of specimens are less than 9%; thus, the prediction models can suitably predict and control the geometric characteristics of a multi-layer cladding structure. The proposed optimization of process parameters can significantly improve the geometric quality of parts and has substantial value in engineering applications. [ABSTRACT FROM AUTHOR]

Operations and maintenance (O&M) of floating offshore wind turbines (FOWTs) require regular inspection activities to predict, detect, and troubleshoot faults at high altitudes and in harsh environments such as strong winds, waves, and tides. Their costs typically account for more than 30% of the lifetime cost due to high labor costs and long downtime. Different inspection methods, including manual inspection, permanent sensors, climbing robots, remotely operated vehicles (ROVs), and unmanned aerial vehicles (UAVs), can be employed to fulfill O&M missions. The UAVs, as an enabling technology, can deal with time and space constraints easily and complete tasks in a cost-effective and efficient manner, which have been widely used in different industries in recent years. This study provides valuable insights into the existing applications of UAVs in FOWT inspection, highlighting their potential to reduce the inspection cost and thereby reduce the cost of energy production. The article introduces the rationale for applying UAVs to FOWT inspection and examines the current technical status, research gaps, and future directions in this field by conducting a comprehensive literature review over the past 10 years. This paper will also include a review of UAVs' applications in other infrastructure inspections, such as onshore wind turbines, bridges, power lines, solar power plants, and offshore oil and gas fields, since FOWTs are still in the early stages of development. Finally, the trends of UAV technology and its application in FOWTs inspection are discussed, leading to our future research direction.