Contact-aided Compliant Mechanisms Research Articles

Design and pre-clinical evaluation of a folding magnetic anastomosis device for minimally invasive surgery

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.

Miniature Flexible Instrument with Fibre Bragg Grating-Based Triaxial Force Sensing for Intraoperative Gastric Endomicroscopy.

Optical biopsy methods, such as probe-based endomicroscopy, can be used to identify early-stage gastric cancer in vivo. However, it is difficult to scan a large area of the gastric mucosa for mosaicking during endoscopy. In this work, we propose a miniaturised flexible instrument based on contact-aided compliant mechanisms and fibre Bragg grating (FBG) sensing for intraoperative gastric endomicroscopy. The instrument has a compact design with an outer diameter of 2.7 mm, incorporating a central channel with a diameter of 1.9 mm for the endomicroscopic probe to pass through. Experimental results show that the instrument can achieve raster trajectory scanning over a large tissue surface with a positioning accuracy of 0.5 mm. The tip force sensor provides a 4.6 mN resolution for the axial force and 2.8 mN for transverse forces. Validation with random samples shows that the force sensor can provide consistent and accurate three-axis force detection. Endomicroscopic imaging experiments were conducted, and the flexible instrument performed no gap scanning (mosaicking area more than 3 mm2) and contact force monitoring during scanning, demonstrating the potential of the system in clinical applications.

A Multi-Contact-Aided Continuum Manipulator With Anisotropic Shapes

Cable-driven continuum manipulators have shown excellent benefits to work for endoluminal intervention. Demand of small diameter for confined anatomy limits the usage of multiple actuations, leading to limited DOFs and bending shapes. To address this problem, this letter proposes a multi-contact-aided continuum manipulator with anisotropic bending shapes. First, contact-aided compliant mechanisms (CCMs) are configured at different locations to introduce the specific constraints to enable the anisotropy. Then, the forward and inverse kinematic models considering contact blocks are built. The reachable workspace of the continuum manipulator is given, and simulation cases are studied to demonstrate the superiority of the proposed manipulator. Finally, a 3D-printed physical prototype is fabricated, and preliminary experiments are conducted to evaluate the model accuracy. Results show an average shape error of 1.98 mm (4.2%) and a maximum of 3.58 mm (7.6%). A robotic bronchoscopy platform integrated with the continuum manipulator is developed to conduct the airway phantom experiments. The shape deviation of the proposed manipulator from the centerline of the bronchus is 31.8% smaller than that of the constant curvature manipulator. The experiments validate the system-level feasibility and effectiveness of the developed continuum manipulator.

Topology Synthesis of a Three-Kink Contact-Aided Compliant Switch

Abstract A topology synthesis approach to design 2D contact-aided compliant mechanisms (CCMs) to trace output paths with three or more kinks is presented. Synthesis process uses three different types of external, rigid contact surfaces—circular, elliptical, and rectangular—which in combination, offer intricate local curvatures that CCMs can benefit from, to deliver desired, complex output characteristics. A network of line elements is employed to generate topologies. A set of circular subregions is laid over this network, and external contact surfaces are generated within each subregion. Both discrete and continuous design variables are employed–the former set controls the CCM topology, appearance and type of external contact surfaces, whereas the latter set governs shapes and sizes of the CCM constituents and sizes of contact surfaces. All contact types are permitted with contact modeling made significantly easier through identification of outer and inner loops. Line topologies are fleshed out via a user-defined number of quadrilateral elements along lateral and longitudinal directions. Candidate CCM designs are carefully preprocessed before analysis via a commercial software and evolved using a stochastic search. The process is exemplified via a contact-aided, three-kink mechanical switch which is thoroughly analyzed in the presence of friction and wear.

Modeling and Task-Oriented Optimization of Contact-Aided Continuum Robots

Steerable catheters, as one type of continuum robot, has been popularly used to reach targets to treat atrial fibrillation. Its tip orientation relative to the surface normal of anatomy affects the ablation efficiency and lesion volume. Traditional catheters with a constant deflection have to rely on the reaction force from the tissue to reach targets, and their tip orientation capability is always limited. To overcome this challenge, we propose a miniaturized tendon actuated continuum robot with asymmetric contact-aided compliant mechanisms (CCMs) to generate asymmetric bends. It can adapt to the confined space and improve the tip orientation capability. The general configuration with the customized contact-aided segments and spatial arrangements is investigated. A mechanical model considering self-contacts and tendon interactions is built to describe free bends and constrained bends. A task-oriented optimization based on the mechanical model is implemented to find the best asymmetric configuration with unevenly distributed CCMs. Experiments are carried out to validate the proposed design, model, and optimization. Comparisons of continuum robots with and without CCMs by experiments and simulation demonstrate its potential advantages to improve the deflection and tip orientation in the confined space.

Large-Deflection Analysis of General Beams in Contact-Aided Compliant Mechanisms Using Chained Pseudo-Rigid-Body Model

Abstract The nonlinear analysis and design of contact-aided compliant mechanisms (CCMs) are challenging. This paper presents a nonlinear method for analyzing the deformation of general beams that contact rigid surfaces in CCMs. The large deflection of the general beam is modeled by using the chained pseudo-rigid-body model. A geometry constraint from the contact surface is developed to constrain the beam’s deformed configuration. The contact analysis problem is formulated based on the principle of minimum potential energy and solved using an optimization algorithm. Besides, a novel technique based on the principle of work and energy is proposed to calculate the reaction force/moment of displacement-loaded cases. Several analysis examples of the compliant mechanisms with straight or curved beams are used to verify the proposed method. The results show that the proposed method and technique can evaluate the deformation of beam-based CCMs and the reaction force/moment with acceptable accuracy, respectively.

A CPRBM-based method for large-deflection analysis of contact-aided compliant mechanisms considering beam-to-beam contacts

Contact-aided compliant mechanisms (CCMs) utilize contact to achieve enhanced functionality. The contact phenomenon of CCMs increases the difficulties of their analysis and design, especially when they exhibit beam-to-beam contact. Considering the particularity of CCMs analysis, which is more about the mechanisms’ deformation, this paper presents a numerical method to analyze the large deflection and stress of the CCMs considering beam-to-beam contacts. Based on our previous work on beam-to-rigid contact, the large deformation of general beams in CCMs is modeled by using the chained pseudo-rigid-body model (CPRBM). An approximation based on the geometric information of CPRBM is proposed in this paper to rapidly determine the moving boundary curve for beam-to-beam contact constraints. The static equilibrium configuration of CCMs is solved by minimizing its potential energy function under the geometric constraints from the boundary curves of contacts. A formulation is also provided to evaluate the normal stress along the deformed beam based on the deformation of CPRBM’s torsional springs. Numerical examples and finite element analysis are used to verify the feasibility and accuracy of the proposed method.

Tailoring energy absorption with functional grading of a contact-aided compliant mechanism

Functional grading can be used for spatial control of local mechanical properties and control of the stiffness and energy absorption of a structure. Cellular contact-aided compliant mechanisms (C3M) are cellular structures with integrated self-contact mechanisms, i.e. the compliant segments experience self-contact during deformation. The contact changes the load path and the C3M cells can be tailored for a specific structural application, such as energy absorption. The focus of the paper is on C3M made of nickel titanium which exploit self contact, the superelastic effect, and functional grading to improve performance and increase energy absorption. Continuous and discrete functional grading models are implemented in finite element analyses of the C3M cells. It is found that there is a complex relationship among self contact, superelastic properties, and functional grading, which are tailored to improve the performance of C3M. The functionally graded cells can be realized through metal additive manufacturing of NiTi, where functional grading and superelasticity are achieved by varying the material composition locally.

Design optimization of a contact-aided continuum robot for endobronchial interventions based on anatomical constraints

PurposeA laser-profiled continuum robot (CR) with a series of interlocking joints has been developed in our center to reach deeper areas of the airways. However, it deflects with constant curvature, which thus increases the difficulty of entering specific bronchi without relying on the tissue reaction forces. This paper aims to propose an optimization framework to find the best design parameters for nonconstant curvature CRs to reach distal targets while attempting to avoid the collision with the surrounding tissue.MethodsFirst, the contact-aided compliant mechanisms (CCMs) are integrated with the continuum robot to achieve the nonconstant curvature. Second, forward kinematics considering CCMs is built. Third, inverse kinematics is implemented to steer the robot tip toward the desired targets within the confined anatomy. Finally, an optimization framework is proposed to find the best robot design to reach the target with the least collision to the bronchi walls.ResultsExperiments are carried out to verify the feasibility of CCMs to enable the nonconstant curvature deflection, and simulations demonstrate a lower cost function value to reach a target for the nonconstant curvature optimized design with respect to the standard constant curvature robot (0.11 vs. 2.66). In addition, the higher capacity of the optimized design to complete the task is validated by interventional experiments using fluoroscopy.ConclusionResults demonstrate the effectiveness of the proposed framework to find an optimized CR with nonconstant curvature to perform safer interventions to reach distal targets.

Computational Synthesis of Large Deformation Compliant Mechanisms Undergoing Self and Mutual Contact

Topologies of large deformation contact-aided compliant mechanisms (CCMs), with self and mutual contact, exemplified via path generation applications, are designed using the continuum synthesis approach. Design domain is parameterized using honeycomb tessellation. Assignment of material to each cell, and generation of rigid contact surfaces, are accomplished via suitably sizing and positioning negative circular masks using the stochastic hill-climber search. To facilitate contact analysis, boundary smoothing is implemented. Mean value coordinates are employed to compute shape functions, as many regular hexagonal cells get degenerated into irregular, concave polygons as a consequence of boundary smoothing. Both geometric and material nonlinearities are considered. The augmented Lagrange multiplier method with a formulated active set strategy is employed to incorporate both self and mutual contact. Synthesized contact-aided compliant continua trace paths with single, and importantly, multiple kinks and experience multiple contact interactions pertaining to both self and mutual contact modes.

Dual Optimization of Contact-Aided Compliant Mechanisms for Passive Dynamic Shape Change

A dual optimization method for optimizing contact-aided compliant mechanism design parameters and their spatial distribution in a dynamic ornithopter wing structure for increased pitch agility is presented. This methodology separates the task into two separate optimization problems where, first, a computationally efficient rigid-body dynamics model is used to determine the optimal stiffness and spatial distribution of the compliant mechanisms and, second, a detailed compliant mechanism design is developed and optimized that achieves the desired nonlinear stiffness. A rigid-body mechanics model of the wing structure is used to find the location and stiffness of a contact-aided compliant mechanism that will induce the forward sweep passively by coupling lift loads to forward sweep. The forward-swept compliant mechanism is then developed and optimized to achieve the desirable coupling. The free-flight pitch agility of an ornithopter is shown to increase via sweeping the wings forward during downstroke. A free-flight experiment is performed, and the novel contact-aided compliant mechanism is shown to induce the desired forward sweep during downstroke.

Tuning of a Rigid-Body Dynamics Model of a Flapping Wing Structure With Compliant Joints

A method for validating rigid-body models of compliant mechanisms under dynamic loading conditions using motion tracking cameras and genetic algorithms is presented. The compliant mechanisms are modeled using rigid-body mechanics as compliant joints (CJ): spherical joints with distributed mass and three-axis torsional spring dampers. This allows compliant mechanisms to be modeled using computationally efficient rigid-body dynamics methods, thereby allowing a model to determine the desired stiffness and location characteristics of compliant mechanisms spatially distributed into a structure. An experiment was performed to validate a previously developed numerical dynamics model with the goal of tuning unknown model parameters to match the flapping kinematics of the leading edge spar of an ornithopter with contact-aided compliant mechanisms (CCMs), compliant mechanisms that feature self-contact to produce nonlinear stiffness, inserted. A system of computer motion tracking cameras was used to record the kinematics of reflective tape and markers placed along the leading edge spar with and without CCMs inserted. A genetic algorithm was used to minimize the error between the model and experimental marker kinematics. The model was able to match the kinematics of all markers along the spars with a root-mean-square error (RMSE) of less than 2% of the half wingspan over the flapping cycle. Additionally, the model was able to capture the deflection amplitude and harmonics of the CCMs with a RMSE of less than 2 deg over the flapping cycle.

Synthesis of C0 Path-Generating Contact-Aided Compliant Mechanisms Using the Material Mask Overlay Method

Contact-aided compliant mechanisms (CCMs) are synthesized via the material mask overlay strategy (MMOS) to trace desired nonsmooth paths. MMOS employs hexagonal cells to discretize the design region and engages negative circular masks to designate material states. To synthesize CCMs, the modified MMOS presented herein involves systematic mutation of five mask parameters through a hill climber search to evolve not only the continuum topology but also to position the rigid, interacting surfaces within some masks. To facilitate analysis with contact, boundary smoothing is performed by shifting boundary nodes of the evolving continuum. Various geometric singularities are subdued via hexagonal cells, and the V-notches at the continuum boundaries are alleviated. Numerous hexagonal cells get morphed into concave subregions as a consequence. Large deformation finite-element formulation with mean-value coordinates based shape functions is used to cater to the generic hexagonal shapes. Contact analysis is accomplished via the Newton–Raphson (NR) iteration with load incrementing in conjunction with the augmented Lagrange multiplier method and active set constraints. An objective function based on Fourier shape descriptors (FSDs) is minimized subject to suitable design constraints. Two examples of path-generating CCMs are presented, their performance compared with a commercial software and fabricated to establish the efficacy of the proposed synthesis method.

Design of contact-aided compliant cellular mechanisms with curved walls

Contact-aided compliant cellular mechanisms are cellular structures designed with contact mechanisms integrated into each cell to provide stress relief. This article addresses compliant cellular structures having curved walls and internal contact mechanisms. The use of curved walls in cellular structures tends to improve their performance in terms of global strain capability and is beneficial for fabrication. In some cells, the addition of contact mechanisms results in stress relief, allowing the cells to be stretched farther than they could without contact. The cellular structures with curved walls are modeled, and finite element analysis is used to calculate the maximum global strains for comparable noncontact and contact-aided cells. An optimization procedure is performed to find the cell geometries that result in the highest global strains. Strains of up to 32.4% and 19.7% are predicted for the optimized curved noncontact and contact-aided cells, respectively. Additionally, a comparison of curved and noncurved, noncontact and contact-aided cells shows that the addition of curved walls results in a significantly greater improvement in global strains than that gained by adding a contact mechanism. Mesoscale contact-aided compliant cellular mechanism designs are fabricated via the lost mold–rapid infiltration forming process and are tested using a custom-designed test rig.

Stress Relief in Contact-Aided Compliant Cellular Mechanisms

Compliant cellular structures with an internal contact mechanism are described in this paper. Contact during deformation reduces failure-causing bending stresses through stress relief, thereby enabling such cellular structures to be stretched more than the corresponding structures without contact. Finite element analysis (FEA) is carried out to simulate the structure. An analytical model is developed to get results quicker than FEA and to develop insight into the mechanics of the deformation process. The error in prediction of the maximum stretching capacity using the analytical model is less than 7% when compared with finite element simulations. Several materials are investigated for such structures. Although the allowable strain of all these materials is small, the overall strain of the contact-aided cellular structures is at least an order of magnitude greater than that of the constitutive material. The contact mechanism and the induced stress relief increase the stretching capacity of the contact-aided cellular structures by as much as 100%. Experiments are conducted to validate the models, and good agreement is found. A high-strain morphing aircraft skin is examined as an application of these mechanisms. The results indicate that the proposed skin structure not only increases the morphing capacity but also decreases the structural mass by 13% as compared with a cellular skin without contact.

A Novel Compliant Mechanism for Converting Reciprocating Translation Into Enclosing Curved Paths

This paper introduces a novel contact-aided compliant mechanism that uses intermittent contacts to convert a single translatory reciprocating input into two output curves, which intersect to enclose a two dimensional region. Contact interactions endow contact-aided compliant mechanisms with enhanced kinematic and kinetostatic capabilities. The mechanism described in this paper is designed to undergo large deformations repeatedly, without yielding by avoiding flexural joints and by using contacts to obtain the desired deformation. A single-material, joint-free and planar design makes the mechanism easy and economical to fabricate at the macro or micro scales. The design is validated experimentally by manufacturing and testing macro scale prototypes. Two potential applications that motivated this mechanism are also noted.

Topology optimization for synthesis of contact-aided compliant mechanisms using regularized contact modeling

A topology optimization technique for systematically designing contact-aided compliant mechanisms (CCM) is presented in this paper. A CCM is a single piece elastic body that uses intermittent contacts in addition to elastic deformation to transmit force and motion. Contact interactions give rise to interesting nonlinear and nonsmooth behaviors even under the small deflection assumption made in this work. The difficulties associated with the nondifferentiability inherent in the CCM systematic synthesis problem are circumvented by using a regularized contact model. This model uses a smooth approximation of the unilateral displacement constraints that are used to model contact interactions. The use of a regularized contact model in the underlying state problem makes it possible to use efficient smooth optimization algorithms for the systematic synthesis of CCMs. The formulation of the design problem for CCMs, sensitivity analysis, and solution methodology are presented. The paper includes CCM designs that exhibit nonsmooth motion and force transmission characteristics, which are not possible or practical with compliant mechanisms that do not use intermittent contact interactions.