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Journal articles on the topic 'Variable-Stiffness Compliant Mechanism'

Author: Grafiati
Published: 4 June 2021
Last updated: 17 February 2022

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1

HAYASHI, Kouji, Jyunya ABE, Hisashi NAITO, Takeshi MATSUMOTO, and Masao TANAKA. "307 Optimum Design of Variable Stiffness Structure with Compliant Mechanism." Proceedings of Conference of Kansai Branch 2010.85 (2010): _3–13_. http://dx.doi.org/10.1299/jsmekansai.2010.85._3-13_.

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2

H Lugo, Jesus. "Simultaneous position and stiffness control of a revolute joint using a biphasic media variable stiffness actuator." International Journal of Robotic Computing 1, no. 2 (December 1, 2019): 80–97. http://dx.doi.org/10.35708/rc1868-126252.

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Safe interactions between humans and robots are needed in several industrial processes and service tasks. Compliance design and control of mechanisms is a way to increase safety. This article presents a compliant revolute joint mechanism using a biphasic media variable stiffness actuator. The actuator has a member configured to transmit motion that is connected to a fluidic circuit, into which a biphasic control fluid circulates. Stiffness is controlled by changing pressure of control fluid into distribution lines. A mathematical model of the actuator is presented, a model-based control method is implemented to track the desired position and stiffness, and equations relating to the dynamics of the mechanism are provided. Results from force loaded and unloaded simulations and experiments with a physical prototype are discussed. The additional information covers a detailed description of the system and its physical implementation.
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Zhang, Xiang, Twan Capehart, and Carl A. Moore. "Design and Analysis of a Novel Variable Stiffness Joint for Robot." MATEC Web of Conferences 249 (2018): 03005. http://dx.doi.org/10.1051/matecconf/201824903005.

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As people pay more attention to the safety of human-robotic interaction, the flexibility of machine joints is becoming more and more important. To address the needs of future robotic applications, many kinds of variable stiffness mechanisms have been designed by scientists. But most of the structures are complex. By studying and comparing many different mechanism designs of variable stiffness joint, we recognize the need to miniaturization and reduce weight of variable stiffness joints with high frequency operation. To address this, need a continuously Variable Compliant Joint (CVCJ) was designed. The core of the joint is based on the structure of the spherical continuously variable transmission (SCVT) which is the catalyst to change the stiffness continuously and smoothly. In this paper, we present a compact variable stiffness joint structure to meet the volume and weight requirements of the future robotic systems. We show the connection between the joint stiffness coefficient and the structure parameters by making mathematical analysis, modelling and simulation for the system to verify the ability to satisfy the base application requirements of the compliant joint.
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4

Zeng, Xianpai, Cart Hurd, Hai-Jun Su, Siyang Song, and Junmin Wang. "A parallel-guided compliant mechanism with variable stiffness based on layer jamming." Mechanism and Machine Theory 148 (June 2020): 103791. http://dx.doi.org/10.1016/j.mechmachtheory.2020.103791.

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5

Cestari, M., D. Sanz-Merodio, J. C. Arevalo, and E. Garcia. "ARES, a variable stiffness actuator with embedded force sensor for the ATLAS exoskeleton." Industrial Robot: An International Journal 41, no. 6 (October 20, 2014): 518–26. http://dx.doi.org/10.1108/ir-06-2014-0350.

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Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected. Originality/value – In the actuator, the compliant elements simultaneously allow measuring of the torque exerted by the join. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected.
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6

Ayoubi, Younsse, Med Amine Laribi, Marc Arsicault, and Saïd Zeghloul. "Safe pHRI via the Variable Stiffness Safety-Oriented Mechanism (V2SOM): Simulation and Experimental Validations." Applied Sciences 10, no. 11 (May 30, 2020): 3810. http://dx.doi.org/10.3390/app10113810.

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Robots are gaining a foothold day-by-day in different areas of people’s lives. Collaborative robots (cobots) need to display human-like dynamic performance. Thus, the question of safety during physical human–robot interaction (pHRI) arises. Herein, we propose making serial cobots intrinsically compliant to guarantee safe pHRI via our novel designed device, V2SOM (variable stiffness safety-oriented mechanism). Integrating this new device at each rotary joint of the serial cobot ensures a safe pHRI and reduces the drawbacks of making robots compliant. Thanks to its two continuously linked functional modes—high and low stiffness—V2SOM presents a high inertia decoupling capacity, which is a necessary condition for safe pHRI. The high stiffness mode eases the control without disturbing the safety aspect. Once a human–robot (HR) collision occurs, a spontaneous and smooth shift to low stiffness mode is passively triggered to safely absorb the impact. To highlight V2SOM’s effect in safety terms, we consider two complementary safety criteria: impact force (ImpF) criterion and head injury criterion (HIC) for external and internal damage evaluation of blunt shocks, respectively. A pre-established HR collision model is built in Matlab/Simulink (v2018, MathWorks, France) in order to evaluate the latter criterion. This paper presents the first V2SOM prototype, with quasi-static and dynamic experimental evaluations.
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7

Mekaouche, Adel, Frédéric Chapelle, and Xavier Balandraud. "A compliant mechanism with variable stiffness achieved by rotary actuators and shape-memory alloy." Meccanica 53, no. 10 (March 29, 2018): 2555–71. http://dx.doi.org/10.1007/s11012-018-0844-0.

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8

Ayoubi, Younsse, Med Laribi, Said Zeghloul, and Marc Arsicault. "V2SOM: A Novel Safety Mechanism Dedicated to a Cobot’s Rotary Joints." Robotics 8, no. 1 (March 6, 2019): 18. http://dx.doi.org/10.3390/robotics8010018.

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Unlike “classical” industrial robots, collaborative robots, known as cobots, implement a compliant behavior. Cobots ensure a safe force control in a physical interaction scenario within unknown environments. In this paper, we propose to make serial robots intrinsically compliant to guarantee safe physical human–robot interaction (pHRI), via our novel designed device called V2SOM, which stands for Variable Stiffness Safety-Oriented Mechanism. As its name indicates, V2SOM aims at making physical human–robot interaction safe, thanks to its two basic functioning modes—high stiffness mode and low stiffness mode. The first mode is employed for normal operational routines. In contrast, the low stiffness mode is suitable for the safe absorption of any potential blunt shock with a human. The transition between the two modes is continuous to maintain a good control of the V2SOM-based cobot in the case of a fast collision. V2SOM presents a high inertia decoupling capacity which is a necessary condition for safe pHRI without compromising the robot’s dynamic performances. Two safety criteria of pHRI were considered for performance evaluations, namely, the impact force (ImpF) criterion and the head injury criterion (HIC) for, respectively, the external and internal damage evaluation during blunt shocks.
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9

Zou, Liangliang, Jin Yuan, Xuemei Liu, Jinguang Li, Ping Zhang, and Ziru Niu. "Burgers viscoelastic model-based variable stiffness design of compliant clamping mechanism for leafy greens harvesting." Biosystems Engineering 208 (August 2021): 1–15. http://dx.doi.org/10.1016/j.biosystemseng.2021.05.007.

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10

Wang, Mingyuan, and Lubin Hang. "Research and application of variable DOF compliant five-bar mechanism based on novel compliant torsion joint in vehicle side door latch." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 234, no. 19 (April 20, 2020): 3789–808. http://dx.doi.org/10.1177/0954406220917423.

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In this paper, a novel compliant joint with torsion spring (CJTS) is proposed in order to realize the power release (Note: The “power release” feature means that the closure system with a latch assembly including a pawl-ratchet release mechanism is controlled by at least one electric actuator.) feature of the vehicle side door latch. A new type of variable degree of freedom (DOF) compliant five-bar mechanism (VDCM) based on the novel compliant joint is constructed. The novel compliant mechanism is characterized by multiple motion modes of planar five-bar mechanism and four-joint, crank-shaper, crank-oscillating block mechanism. These motion modes can be switched through the different choices of driving joints and limiting stoppers. This compliant mechanism is effectively implanted into a vehicle side door latch as a sub-branch to perform power release function. The force-adaptive characteristic of the VDCM ensures compatibility with extant manual release branches. Drifting displacement of the CJTS’s torsion spring rotation center in the groove is proposed as a compliant index to describe the compatibility and force-adaptive characteristics under various working modes. The relationship between torsion spring stiffness and mechanism characteristic point motion trajectory or position recovery time duration or motion accuracy is studied. The results show that the introduction of compatibility and force-adaptive characteristics is able to reduce the shaking forces exerted on the mechanism frame. The shaking forces will be further reduced by changing equivalent mass center position of the component. Furthermore, the practicability of the novel compliant mechanism is experimentally validated on the force-displacement test platform. The work in this paper provides a reference for the multi-mode motion mechanical design in a confined space of the latch.
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11

Cui, Zuo, and Hongzhou Jiang. "Design, analysis, and simulation of a planar serial–parallel mechanism for a compliant robotic fish with variable stiffness." Advances in Mechanical Engineering 8, no. 8 (August 2016): 168781401666092. http://dx.doi.org/10.1177/1687814016660927.

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12

Jafari, Amir, Nikos Tsagarakis, and Darwin Caldwell. "Energy efficient actuators with adjustable stiffness: a review on AwAS, AwAS-II and CompACT VSA changing stiffness based on lever mechanism." Industrial Robot: An International Journal 42, no. 3 (May 18, 2015): 242–51. http://dx.doi.org/10.1108/ir-12-2014-0433.

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Purpose This paper aims to discuss, analyze and compare members of a group of actuators with adjustable stiffness, namely: AwAS, AwAS-II and CompACT variable stiffness actuator (VSA) developed at Italian Institute of Technology (IIT). Design/methodology/approach These actuators are among series type of VSAs where one main motor is dedicated for link positioning and a secondary motor, in series with the first one, regulates the output link stiffness. Regulating the stiffness in this group of actuators is based on the lever concept. Initially, springs were moved along the lever to tune the stiffness while in the later versions stiffness was regulated through relocating pivot point along the lever. Findings This paper discusses how different mechanisms have been employed in realization of the lever concept in these actuators and what are the advantages and disadvantages of each realization. Practical implications Today’s robots are not supposed to be solid, isolated and rigid anymore but rather adaptive, cooperative and compliant entities in our daily life. The new attitudes demand for novel technologies substantially different from those developed for industrial domains both at the hardware and the software levels. This work presents latest three state-of-the-art actuators, developed at IIT, which are great answers to the needs of tomorrow’s robot. Originality/value These novel actuators are really ready for commercial exploitation, as they are compact and reliable. The main novelty is based on employing concept of lever mechanism for stiffness regulation. They have been designed and manufactured in a very professional and optimized way.
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13

Morrison, Tyler, and Hai-Jun Su. "Stiffness modeling of a variable stiffness compliant link." Mechanism and Machine Theory 153 (November 2020): 104021. http://dx.doi.org/10.1016/j.mechmachtheory.2020.104021.

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14

Ning, Yinghao, Wenfu Xu, Hailin Huang, Bing Li, and Fei Liu. "Design methodology of a novel variable stiffness actuator based on antagonistic-driven mechanism." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 233, no. 19-20 (August 25, 2019): 6967–84. http://dx.doi.org/10.1177/0954406219869968.

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This paper concerns the construction of a novel variable stiffness actuator with antagonistic-driven mechanism (ADM-VSA). The ADM-VSA consists of two cam mechanisms and two constant stiffness spring mechanisms establishing the antagonistic structure to eliminate the empty return journey. The former with symmetrical cam profiles are designed for the movement of actuator, while the latter are explored substituting traditional springs of generating compliance for compact structure. To obtain desired performance of the actuator, the design methodology is developed for constructing the ADM-VSA, integrating the constant stiffness spring mechanism design method from four-bar mechanism to multi-bar mechanism, the comprehensive optimization of cam profiles and sensitivity analysis of structural parameters. The comprehensive optimization is conducted with different-order Bezier splines considering the torque, stiffness, and energy by friction simultaneously. The sensitivity analysis is performed to investigate the influence of structural errors on the performance of actuator, with new indexes decreasing the workload of calculation, and several guidelines for the design and manufacturing are achieved. Finally, a prototype is developed to verify the reliability of ADM-VSA and, further, proves the validity of proposed design methods.
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15

Nalini, D., and K. Dhanalakshmi. "Synergistically configured shape memory alloy for variable stiffness translational actuation." Journal of Intelligent Material Systems and Structures 30, no. 6 (February 22, 2019): 844–54. http://dx.doi.org/10.1177/1045389x19828487.

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The structural composition of two elastic elements, shape memory alloy wire (active actuating element) and spring (the passive bias), offers variable stiffness actuation. Based on this principle, a variable stiffness linear actuator is conceptually designed and developed. It is electromechanical by nature, that is, it is electrically activated and creates translational/linear motion. The variable stiffness linear actuator engages shape memory alloy wire(s) along with a passive compression spring to work synergistically. The biasing element offers recovery force to the shape memory alloy wire as well as compliance to the whole structure. The synergistic configuration exhibits an aiding force, thereby allowing an actuation with large displacement and a wide range of stiffness. The actuator mechanism is implemented through parallel action and further proposes two different modes of operation: pull mode (i.e. the disc moving along a fixed shaft) and push mode (i.e. linear reciprocating motion of the pushrod). The shape memory alloy configured actuator mechanism is analysed theoretically; the working model of the variable stiffness linear actuator is developed and investigated experimentally. The results apprise that the variable stiffness linear actuator is capable of offering large displacement and in reproducing the stiffness profile for active compliance control applications.
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16

Yang, Chenghao, Shineng Geng, Ian Walker, David T. Branson, Jinguo Liu, Jian S. Dai, and Rongjie Kang. "Geometric constraint-based modeling and analysis of a novel continuum robot with Shape Memory Alloy initiated variable stiffness." International Journal of Robotics Research 39, no. 14 (April 13, 2020): 1620–34. http://dx.doi.org/10.1177/0278364920913929.

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Continuum robots exhibit promising adaptability and dexterity for soft manipulation due to their intrinsic compliance. However, this compliance may lead to challenges in modeling as well as positioning and loading. In this paper, a virtual work-based static model is established to describe the deformation and mechanics of continuum robots with a generic rod-driven structure, taking the geometric constraint of the drive rods into account. Following this, this paper presents a novel variable stiffness mechanism powered by a set of embedded Shape Memory Alloy (SMA) springs, which can make the drive rods become ‘locked’ on the body structure with different configurations. The resulting effects of variable stiffness are then presented in the static model by introducing tensions of the SMA and friction on the rods. Compared with conventional models, there is no need to predefine the actuation forces of the drive rods; instead, actuation displacements are used in this new mechanism system with stiffness being regulated. As a result, the phenomenon that the continuum robot can exhibit an S-shaped curve when subject to single-directional forces is observed and analyzed. Simulations and experiments demonstrated that the presented mechanism has stiffness variation of over 287% and further demonstrated that the mechanism and its model are achievable with good accuracy, such that the ratio of positioning error is less than 2.23% at the robot end-effector to the robot length.
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17

Zhu, Jun, Yu Wang, Jinlin Jiang, Bo Sun, and Heng Cao. "Unidirectional variable stiffness hydraulic actuator for load-carrying knee exoskeleton." International Journal of Advanced Robotic Systems 14, no. 1 (January 1, 2017): 172988141668695. http://dx.doi.org/10.1177/1729881416686955.

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This article presents the design and experimental testing of a unidirectional variable stiffness hydraulic actuator for load-carrying knee exoskeleton. The proposed actuator is designed for mimicking the high-efficiency passive behavior of biological knee and providing actively assistance in locomotion. The adjustable passive compliance of exoskeletal knee is achieved through a variable ratio lever mechanism with linear elastic element. A compact customized electrohydraulic system is also designed to accommodate application demands. Preliminary experimental results show the prototype has good performances in terms of stiffness regulation and joint torque control. The actuator is also implemented in an exoskeleton knee joint, resulting in anticipant human-like passive compliance behavior.
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18

Yigit, Cihat Bora, and Pinar Boyraz. "Design and Modelling of a Cable-Driven Parallel-Series Hybrid Variable Stiffness Joint Mechanism for Robotics." Mechanical Sciences 8, no. 1 (March 22, 2017): 65–77. http://dx.doi.org/10.5194/ms-8-65-2017.

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Abstract. The robotics, particularly the humanoid research field, needs new mechanisms to meet the criteria enforced by compliance, workspace requirements, motion profile characteristics and variable stiffness using lightweight but robust designs. The mechanism proposed herein is a solution to this problem by a parallel-series hybrid mechanism. The parallel term comes from two cable-driven plates supported by a compression spring in between. Furthermore, there is a two-part concentric shaft, passing through both plates connected by a universal joint. Because of the kinematic constraints of the universal joint, the mechanism can be considered as a serial chain. The mechanism has 4 degrees of freedom (DOF) which are pitch, roll, yaw motions and translational movement in z axis for stiffness adjustment. The kinematic model is obtained to define the workspace. The helical spring is analysed by using Castigliano's Theorem and the behaviour of bending and compression characteristics are presented which are validated by using finite element analysis (FEA). Hence, the dynamic model of the mechanism is derived depending on the spring reaction forces and moments. The motion experiments are performed to validate both kinematic and dynamic models. As a result, the proposed mechanism has a potential use in robotics especially in humanoid robot joints, considering the requirements of this robotic field.
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Lobontiu, Nicolae, and Ephrahim Garcia. "Circular-Hinge Line Element for Finite Element Analysis of Compliant Mechanisms." Journal of Mechanical Design 127, no. 4 (June 27, 2005): 766–73. http://dx.doi.org/10.1115/1.1825046.

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A three-node six degree-of-freedom per-node line element that is sensitive to axial, bending, and torsional loading is introduced to model single-axis right circular hinges of constant width that are utilized in compliant mechanisms. The Timoshenko model is applied for bending because this particular configuration is virtually short, and provisions are taken that the element is shear-locking free. The Saint Venant theory, which includes warping, is utilized to model torsion of the variable rectangular cross-section circular hinge. The principle of minimum total potential energy is employed to formulate the elemental stiffness and mass matrices, as well as the elemental nodal vector. Static force deflection and modal simulation that are performed based on this finite element model produce results that are in agreement with simulation by commercially available finite element software. The three-node line element is also compared to an analytical model in terms of stiffness and the results are again concurring.
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20

Guo, Jishu. "Conceptual mechanical design of antagonistic variable stiffness joint based on equivalent quadratic torsion spring." Science Progress 103, no. 3 (July 2020): 003685042094129. http://dx.doi.org/10.1177/0036850420941295.

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The variable stiffness joint is a kind of flexible actuator with variable stiffness characteristics suitable for physical human–robot interaction applications. In the existing variable stiffness joints, the antagonistic variable stiffness joint has the advantages of simple implementation of variable stiffness mechanism and easy modular design of the nonlinear elastic element. The variable stiffness characteristics of antagonistic variable stiffness joints are realized by the antagonistic actuation of two nonlinear springs. A novel design scheme of the equivalent nonlinear torsion spring with compact structure, large angular displacement range, and desired stiffness characteristics is presented in this article. The design calculation for the equivalent quadratic torsion spring is given as an example, and the actuation characteristics of the antagonistic variable stiffness joint based on the equivalent quadratic torsion spring are illustrated. Based on the design idea of constructing the antagonistic variable stiffness joint with compact structure and high compliance, as well as the different design requirements of the joints at different positions of the multi–degrees of freedom robot arm, nine types of mechanical schemes of antagonistic variable stiffness joint with the open design concept are proposed in this article. Finally, the conceptual joint configuration schemes of the robot arm based on the antagonistic variable stiffness joint show the application scheme of the designed antagonistic variable stiffness joint in the multi–degrees of freedom robot.
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21

Bottin, Matteo, Silvio Cocuzza, and Matteo Massaro. "Variable Stiffness Mechanism for the Reduction of Cutting Forces in Robotic Deburring." Applied Sciences 11, no. 6 (March 23, 2021): 2883. http://dx.doi.org/10.3390/app11062883.

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One of the main issues related to robotic deburring is that the tool can get damaged or stopped when the burr thickness exceeds a certain threshold. The aim of this work is to devise a mechanism that can reduce cutting forces automatically, in the event that the burr is too high, and is able to return to the baseline configuration when the burr thickness is acceptable again. On the one hand, in normal cutting conditions, the mechanism should have high stiffness to ensure high cutting precision. On the other hand, when the burr is too high the mechanism should exploit its compliance to reduce the cutting forces and, as a consequence, a second cutting cycle will be necessary to completely remove the burr. After the conceptual design of the mechanism and the specification of the desired stiffness curve, the main design parameters of the system are derived thanks to an optimization method. The effectiveness of the proposed mechanism is verified by means of dynamic simulations using selected test cases. A reduction up to 60% of the cutting forces is obtained, considering a steel burr up to 6 mm high.
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22

Tian, Yanling, Mingxuan Yang, Fujun Wang, Chongkai Zhou, Xingyu Zhao, and Dawei Zhang. "A unified element stiffness matrix model for variable cross-section flexure hinges in compliant mechanisms for micro/nano positioning." Microsystem Technologies 25, no. 11 (March 30, 2019): 4257–68. http://dx.doi.org/10.1007/s00542-019-04410-6.

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23

van der Krogt, Marjolein M., Wendy W. de Graaf, Claire T. Farley, Chet T. Moritz, L. J. Richard Casius, and Maarten F. Bobbert. "Robust passive dynamics of the musculoskeletal system compensate for unexpected surface changes during human hopping." Journal of Applied Physiology 107, no. 3 (September 2009): 801–8. http://dx.doi.org/10.1152/japplphysiol.91189.2008.

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When human hoppers are surprised by a change in surface stiffness, they adapt almost instantly by changing leg stiffness, implying that neural feedback is not necessary. The goal of this simulation study was first to investigate whether leg stiffness can change without neural control adjustment when landing on an unexpected hard or unexpected compliant (soft) surface, and second to determine what underlying mechanisms are responsible for this change in leg stiffness. The muscle stimulation pattern of a forward dynamic musculoskeletal model was optimized to make the model match experimental hopping kinematics on hard and soft surfaces. Next, only surface stiffness was changed to determine how the mechanical interaction of the musculoskeletal model with the unexpected surface affected leg stiffness. It was found that leg stiffness adapted passively to both unexpected surfaces. On the unexpected hard surface, leg stiffness was lower than on the soft surface, resulting in close-to-normal center of mass displacement. This reduction in leg stiffness was a result of reduced joint stiffness caused by lower effective muscle stiffness. Faster flexion of the joints due to the interaction with the hard surface led to larger changes in muscle length, while the prescribed increase in active state and resulting muscle force remained nearly constant in time. Opposite effects were found on the unexpected soft surface, demonstrating the bidirectional stabilizing properties of passive dynamics. These passive adaptations to unexpected surfaces may be critical when negotiating disturbances during locomotion across variable terrain.
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Joo, Sangwan, Naotaka Yoshihara, Yasuhiro Masutani, Atsushi Nishikawa, and Fumio Miyazaki. "New Design Methodology for RCC Using Elastomer Shear Pads." Journal of Robotics and Mechatronics 9, no. 5 (October 20, 1997): 362–72. http://dx.doi.org/10.20965/jrm.1997.p0362.

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The mechanical behavior of RCC (Remote-Center-Compliance) devices using elastomer shear pads depends on the number of their elastomer-metal layers, the thickness and radius of the elastomer-metal, and the axial and lateral stiffness of the elastomer. These parameters must be considered in a complete analysis of the design of RCC devices. This paper presents a useful method for analyzing the behavior of RCC devices using elastomer shear pads based on the material mechanics approach. This makes it easy to design new RCCs for specific purposes. Moreover, we have developed a projection/stiffness variable type RCC (VRCC), and verified that a single VRCC duplicates the performance of a wide range of commercially available fixed-type RCCs. Simulation and experimental results are also presented.
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Gao, Jin, and Fuquan Wu. "Analysis and optimization of the vehicle handling stability with considering suspension kinematics and compliance characteristics." Advances in Mechanical Engineering 13, no. 5 (May 2021): 168781402110155. http://dx.doi.org/10.1177/16878140211015523.

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The dynamic model of the front double wishbone suspension and the rear multi-link suspension of the vehicle are established. On the basis of detailed analysis of suspension kinematics, calculation method of wheel alignment angle and force calculation of suspension bushing, the influence mechanism of suspension bushing on the vehicle transient state is clarified, and the vehicle transient characteristic index is derived from the vehicle three-free dynamic model. The sensitivity analysis of the suspension bushing is carried out, and the bushing stiffness which has a great influence on the transient state of the vehicle is obtained. The bushing stiffness scale factor is used as the optimization variable, the vehicle transient characteristic index is used as the optimization target, and the NSGA-II optimization algorithm is used for multi-objective optimization. After optimization, one Pareto solution is selected to compare with the original vehicle, the comparison results show that the yaw rate gain, resonance frequency and delay time of yaw rate in the vehicle transient characteristic index are all improved, other optimization targets change less. In the steady-state comparison, the understeer tendency of the vehicle increases, and the roll angle of the vehicle increases but is within an acceptable range.
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Driels, M., and Lt Yavuz Turkegenci. "Selective Backdriveability and Its Application to a Robotic Finger Design." Journal of Mechanical Design 116, no. 1 (March 1, 1994): 44–46. http://dx.doi.org/10.1115/1.2919374.

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The work reported covers the design of a prototype finger unit which will be part of a dexterous robotic hand design. Unlike conventional designs for contemporary hands which use tendons to actuate individual finger joints, this design uses small electric motors located in the finger units themselves. Because of high gear ratios in the final drive, the finger is able to sustain a grasp with power removed. An implementation of compliant joint control is discussed, and it is shown that this results in an actuation system which not only has variable stiffness control, but one in which the systems inability to be backdriven may be eliminated for those tasks where it is advantageous to do so.
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27

Linß, Sebastian, Philipp Schorr, and Lena Zentner. "General design equations for the rotational stiffness, maximal angular deflection and rotational precision of various notch flexure hinges." Mechanical Sciences 8, no. 1 (March 15, 2017): 29–49. http://dx.doi.org/10.5194/ms-8-29-2017.

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Abstract. Notch flexure hinges are often used as revolute joints in high-precise compliant mechanisms, but their contour-dependent deformation and motion behaviour is currently difficult to predict. This paper presents general design equations for the calculation of the rotational stiffness, maximal angular elastic deflection and rotational precision of various notch flexure hinges in dependence of the geometric hinge parameters. The novel equations are obtained on the basis of a non-linear analytical model for a moment and a transverse force loaded beam with a variable contour height. Four flexure hinge contours are investigated, the semi-circular, the corner-filleted, the elliptical, and the recently introduced bi-quadratic polynomial contour. Depending on the contour, the error of the calculated results is in the range of less than 2 % to less than 16 % for the suggested parameter range compared with the analytical solution. Finite elements method (FEM) and experimental results correlate well with the predictions based on the comparatively simple and concise design equations.
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28

Okabe, Tomonaga, Sota Onodera, Yuta Kumagai, and Yoshiko Nagumo. "Continuum damage mechanics modeling of composite laminates including transverse cracks." International Journal of Damage Mechanics 27, no. 6 (June 5, 2017): 877–95. http://dx.doi.org/10.1177/1056789517711238.

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In this study, the continuum damage mechanics model for predicting the stiffness reduction of composite laminates including transverse cracks is formulated as a function of crack density. To formulate the model, first the damage variable in the direction normal to the fiber of a ply including transverse cracks is derived. The damage variable is derived by the model assuming a plane strain field in the isotropic plane and using the Gudmundson–Zang model for comparison. The effective compliance based on the strain equivalent principle proposed by Murakami et al. and classical laminate theory are then used to formulate the elastic moduli of laminates of arbitrary lay-up configurations as a function of the damage variable. Finally, the results obtained from this model are compared to the finite-element analysis reported in previous studies. The model proposed in this paper can predict the stiffness of laminates containing damage due to transverse cracks (or surface crack) from just the mechanical properties of a ply and the lay-up configurations. Furthermore, this model can precisely predict the finite-element analysis results and experiment results for the elastic moduli of the laminate of arbitrary lay-up configuration, such as cross-ply, angle ply, and quasi-isotropic, including transverse cracks. This model only considers the damage of the transverse crack; it does not consider damage such as delamination. However, this model seems to be effective in the early stage of damage formation when transverse cracking mainly occurs. The model assuming plane strain field in the isotropic plane which is proposed in this paper can calculate the local stress distribution in a ply including transverse cracks as a function of crack density. The damage evolution of transverse cracks can thus be simulated by determining the fracture criterion.
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Ku, C. P. Roger, and H. Heshmat. "Closure to “Discussion of ‘Compliant Foil Bearing Structural Stiffness Analysis: Part I—Theoretical Model Including Strip and Variable Bump Foil Geometry’” (1992, ASME J. Tribol., 114, p. 400)." Journal of Tribology 114, no. 2 (April 1, 1992): 400. http://dx.doi.org/10.1115/1.2926709.

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30

Elelwi, M., T. Calvet, R. M. Botez, and T. M. Dao. "Wing component allocation for a morphing variable span of tapered wing using finite element method and topology optimisation – application to the UAS-S4." Aeronautical Journal 125, no. 1290 (June 7, 2021): 1313–36. http://dx.doi.org/10.1017/aer.2021.29.

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AbstractThis work presents the Topology Optimisation of the Morphing Variable Span of Tapered Wing (MVSTW) using a finite element method. This topology optimisation aims to assess the feasibility of internal wing components such as ribs, spars and other structural components. This innovative approach is proposed for the telescopic mechanism of the MVSTW, which includes the sliding of the telescopically extended wing into the fixed wing segment. The optimisation is performed using the tools within ANSYS Mechanical, which allows the solving of topology optimisation problems. This study aims to minimise overall structural compliance and maximise stiffness to enhance structural performance, and thus to meet the structural integrity requirements of the MVSTW. The study evaluates the maximum displacements, stress and strain parameters of the optimised variable span morphing wing in comparison with those of the original wing. The optimised wing analyses are conducted on four wingspan extensions, that is, 0%, 25%, 50% and 75%, of the original wingspan, and for different flight speeds to include all flight phases (17, 34, 51 and 68m/s, respectively). Topology optimisation is carried out on the solid wing built with aluminium alloy 2024-T3 to distribute the wing components within the fixed and moving segments. The results show that the fixed and moving wing segments must be designed with two spar configurations, and seven ribs with their support elements in the high-strain area. The fixed and moving wing segments’ structural weight values were reduced to 16.3 and 10.3kg from 112 to 45kg, respectively. The optimised MVSTW was tested using different mechanical parameters such as strains, displacements and von Misses stresses. The results obtained from the optimised variable span morphing wing show the optimal mechanical behaviour and the structural wing integrity needed to achieve the multi-flight missions.
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31

Polycarpou, Andreas A., and Andres Soom. "Boundary and Mixed Friction in the Presence of Dynamic Normal Loads: Part I—System Model." Journal of Tribology 117, no. 2 (April 1, 1995): 255–60. http://dx.doi.org/10.1115/1.2831239.

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The instantaneous normal motion between bodies in a sliding contact is an important variable in determining dynamic friction under unsteady sliding conditions. In order to model friction under dynamic conditions, it is therefore necessary to combine a dynamic model of the sliding system with an accurate model of the friction process. In the present work, the nonlinear normal dynamics of a friction test apparatus are described by a linearized model at a particular steady loading and sliding condition in a mixed or boundary-lubricated regime. The geometry is a line contact. The Hertzian bulk contact compliance and film and asperity damping and stiffness characteristics are included as discrete elements. In Part I of the paper, a fifth-order model is developed for the normal dynamics of the system, using both the Eigensystem Realization Algorithm (ERA) and classical experimental modal analysis techniques. In Part II, this system model is combined with a friction model, developed independently, to describe dynamic friction forces under both harmonic and impulsive applied normal loads.
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32

Gu, A. "Discussion: “Compliant Foil Bearing Structural Stiffness Analysis: Part I—Theoretical Model Including Strip and Variable Bump Foil Geometry” (Ku, C.-P. Roger, and Heshmat, H., 1992, ASME J. Tribol., 114, pp. 394–400)." Journal of Tribology 114, no. 2 (April 1, 1992): 400. http://dx.doi.org/10.1115/1.2926708.

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33

Georges, Penelope C., and Paul A. Janmey. "Cell type-specific response to growth on soft materials." Journal of Applied Physiology 98, no. 4 (April 2005): 1547–53. http://dx.doi.org/10.1152/japplphysiol.01121.2004.

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Many cell types respond to forces as acutely as they do to chemical stimuli, but the mechanisms by which cells sense mechanical stimuli and how these factors alter cellular structure and function in vivo are far less explored than those triggered by chemical ligands. Forces arise both from effects outside the cell and from mechanochemical reactions within the cell that generate stresses on the surface to which the cells adhere. Several recent reviews have summarized how externally applied forces may trigger a cellular response (Silver FH and Siperko LM. Crit Rev Biomed Eng 31: 255–331, 2003; Estes BT, Gimble JM, and Guilak F. Curr Top Dev Biol 60: 91–126, 2004; Janmey PA and Weitz DA. Trends Biochem Sci 29: 364–370, 2004). The purpose of this review is to examine the information available in the current literature describing the relationship between a cell and the rigidity of the matrix on which it resides. We will review recent studies and techniques that focus on substrate compliance as a major variable in cell culture studies. We will discuss the specificity of cell response to stiffness and discuss how this may be important in particular tissue systems. We will attempt to link the mechanoresponse to real pathological states and speculate on the possible biological significance of mechanosensing.
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34

Jang, Gang-Won, Myung-Jin Kim, and Yoon Young Kim. "Design Optimization of Compliant Mechanisms Consisting of Standardized Elements." Journal of Mechanical Design 131, no. 12 (November 12, 2009). http://dx.doi.org/10.1115/1.4000531.

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We developed a design method to configure optimal compliant mechanisms consisting of standardized elements such as semirigid beams, hubs, and joints. In the proposed design approach, mechanism compliance is based upon elastic deformations of joint elements made of short elastic beams. To set up the design problem as an optimization problem, a standard ground beam-based topology optimization method is modified to handle compliant mechanisms comprised of design variable-independent semirigid beams and design variable-dependent elastic joints. In the proposed method, unlike structural stiffness maximization problems, intermediate values should appear to allow elastic deformations in the joints. With our approach, reconfiguration design from one existing compliant mechanism to another can be formulated wherein the number of beam element relocation operations is also minimized. This formulation can be useful in minimizing the time and effort required to convert one mechanism to another.
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35

Chandrasekaran, Karthik, Adarsh Somayaji, and Asokan Thondiyath. "A Novel Design for a Compliant Mechanism Based Variable Stiffness Grasper Through Structure Modulation." Journal of Medical Devices, December 14, 2020. http://dx.doi.org/10.1115/1.4049309.

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Abstract Robots utilize graspers for interacting with an environment. Conventional robot graspers are composed of rigid links and are dedicated to perform a particular task. However, such graspers have difficulty conforming to objects of varied shape and exerting varying grasping forces. Soft robotic graspers provide these features through different modalities. However, such modalities that vary the stiffness of soft robotic graspers face issues such as slow response time, requirement of external power packs for operation and low variation of stiffness. A variable stiffness compliant robotic grasper that is simple in design and operation would improve end effectors used in assistive robotics and prostheses where ability to vary stiffness would benefit in handling a wide array of objects. This research presents a novel method of achieving variable stiffness through structural transformations. Current designs utilizing structural transformations do not provide shape conformance while grasping objects. We propose a design for a soft robotic grasper utilizing the concept of stability of structures. This design is capable of adapting to the surface of an object being grasped and can rapidly vary its stiffness. The grasper behavior is modelled using Finite Element Analysis and validated experimentally. Our results demonstrate that structural transformation of flexible elements is a potential solution for achieving variable stiffness in a grasper.
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36

Palli, Gianluca, Giovanni Berselli, Claudio Melchiorri, and Gabriele Vassura. "Design of a Variable Stiffness Actuator Based on Flexures." Journal of Mechanisms and Robotics 3, no. 3 (July 19, 2011). http://dx.doi.org/10.1115/1.4004228.

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Variable stiffness actuators can be used in order to achieve a suitable trade-off between performance and safety in robotic devices for physical human–robot interaction. With the aim of improving the compactness and the flexibility of existing mechanical solutions, a variable stiffness actuator based on the use of flexures is investigated. The proposed concept allows the implementation of a desired stiffness profile and range. In particular, this paper reports a procedure for the synthesis of a fully compliant mechanism used as a nonlinear transmission element, together with its experimental characterization. Finally, a preliminary prototype of the overall joint is depicted.
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Zhang, Ming, Lijin Fang, Feng Sun, and Koichi Oka. "A Novel Wire-Driven Variable-Stiffness Joint Based on a Permanent Magnetic Mechanism." Journal of Mechanisms and Robotics 11, no. 5 (July 8, 2019). http://dx.doi.org/10.1115/1.4043684.

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The variable-stiffness joint (VSJ) plays an important role in creating compliant and powerful motions. This paper presents a novel wire-driven VSJ based on a permanent magnetic mechanism (PMM). The proposed joint regulates the joint stiffness with lower energy consumption through a wide range via the permanent magnetic mechanism. This effect possibly depends on the novel nonlinear combination of a permanent magnet-spring and wire-driven system that achieves the same stiffness with lower wire tension. A trapezoidal layout of the joint is proposed. Because of the relationship among the stiffness, the position of the joint and the stiffness of the PMM, the stiffness model is also been established. Based on this model, the decoupling controller is built to independently control the position and stiffness of the joint. Experiments show that the VSJPMM achieves position and stiffness independently and also reduces energy and power required to regulate the stiffness compared with the traditional approach. In addition, the proposed mechanism displays a powerful motion and short stiffness adjustment time.
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38

Lemerle, Simon, Manuel G. Catalano, Antonio Bicchi, and Giorgio Grioli. "A Configurable Architecture for Two Degree-of-Freedom Variable Stiffness Actuators to Match the Compliant Behavior of Human Joints." Frontiers in Robotics and AI 8 (March 12, 2021). http://dx.doi.org/10.3389/frobt.2021.614145.

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Living beings modulate the impedance of their joints to interact proficiently, robustly, and safely with the environment. These observations inspired the design of soft articulated robots with the development of Variable Impedance and Variable Stiffness Actuators. However, designing them remains a challenging task due to their mechanical complexity, encumbrance, and weight, but also due to the different specifications that the wide range of applications requires. For instance, as prostheses or parts of humanoid systems, there is currently a need for multi-degree-of-freedom joints that have abilities similar to those of human articulations. Toward this goal, we propose a new compact and configurable design for a two-degree-of-freedom variable stiffness joint that can match the passive behavior of a human wrist and ankle. Using only three motors, this joint can control its equilibrium orientation around two perpendicular axes and its overall stiffness as a one-dimensional parameter, like the co-contraction of human muscles. The kinematic architecture builds upon a state-of-the-art rigid parallel mechanism with the addition of nonlinear elastic elements to allow the control of the stiffness. The mechanical parameters of the proposed system can be optimized to match desired passive compliant behaviors and to fit various applications (e.g., prosthetic wrists or ankles, artificial wrists, etc.). After describing the joint structure, we detail the kinetostatic analysis to derive the compliant behavior as a function of the design parameters and to prove the variable stiffness ability of the system. Besides, we provide sets of design parameters to match the passive compliance of either a human wrist or ankle. Moreover, to show the versatility of the proposed joint architecture and as guidelines for the future designer, we describe the influence of the main design parameters on the system stiffness characteristic and show the potential of the design for more complex applications.
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39

Hampali, Shamanth, Anoosha Pai S, and G. K. Ananthasuresh. "A Tunable Variable-Torque Compliant Hinge Using Open-Section Shells." Journal of Mechanisms and Robotics 12, no. 6 (July 17, 2020). http://dx.doi.org/10.1115/1.4047440.

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Abstract This paper is concerned with a compliant-hinge mechanism that can provide a wide range of torque-angle profiles. The mechanism consists of thin-walled open-section shells that are subjected to combined twisting and bending. A pair of open-section shells is so arranged as to get a large rotation about a virtual axis with high stiffness along other axes. A replaceable cam-like guideway regulates the bending of the open-section shells as they twist, thereby generating the desired torque profile. An energy-based, graphical, and computational design method is formulated to obtain the guideway profile for a specified torque profile. A physical prototype is constructed for an assistive chair for the elderly to demonstrate the variable-torque output and the efficacy of the hinge.
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40

Le, Loan, Matteo Zoppi, Michal Jilich, Han Bo, Dimiter Zlatanov, and Rezia Molfino. "Application of a Biphasic Actuator in the Design of the CloPeMa Robot Gripper." Journal of Mechanisms and Robotics 7, no. 1 (February 1, 2015). http://dx.doi.org/10.1115/1.4029292.

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The paper (a first version of this work was presented in Aug. 2014 at ASME-DETC in Buffalo, NY) describes a novel robot gripper for garment handling. The device has been designed, developed, prototyped, and tested within the CloPeMa European Project creating a robot system for automated manipulation of clothing and other textile items. The gripper has two degrees of freedom (dof) and includes both rigid and flexible elements. A variable-stiffness actuator has been implemented to add controlled compliance in the gripper’s operation allowing the combining of various grasping and manipulation tasks. First, we analyze the specific application-determined task requirements, focusing on the need for adaptive flexibility and the role of compliant elements in the design. The chosen solution is a simple planar mechanism, equipped with one standard and one variable-stiffness actuator. The mechanical design of the gripper, including the hydraulic system used in the biphasic actuator, is outlined, and the control architecture, using sensor feedback, is described.
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41

Banerjee, Hritwick, Tai Kai Li, Godwin Ponraj, Senthil Kumar Kirthika, Chwee Ming Lim, and Hongliang Ren. "Origami-Layer-Jamming Deployable Surgical Retractor With Variable Stiffness and Tactile Sensing." Journal of Mechanisms and Robotics 12, no. 3 (January 14, 2020). http://dx.doi.org/10.1115/1.4045424.

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Abstract Origami-based flexible, compliant, and bio-inspired robots are believed to permit a range of medical applications within confined environments. In this article, we experimentally demonstrated an origami-inspired deployable surgical retractor with the controllable stiffness mechanism that can facilitate safer instrument–tissue interaction in comparison to their rigid counterparts. When controllable negative-pressure is applied to the jammed origami retractor module, it becomes more rigid, increasing its strength. To quantify origami-modules strength further, we demonstrated performances of retractor based on the Daler–Rowney Canford paper (38 grams per square meter (gsm)) and sandpaper of 1000 grit. Experiments on the proposed retractor prototype elucidated sandpaper-based retractor can outperform paper-38-gsm retractor for facelift incision with the width of more than 9 cm. Though 38 gsm Canford paper comprised of thin layers, 16 times lesser in thickness than sandpaper, experiments proved its comparable layer jamming (LJ) performance. We leverage the advantage of the LJ mechanism to tune retractor stiffness, allowing the instrument to hold and separate a facelift incision to mitigate the likelihood of surgical complications. The retractor is equipped with a custom-made printed conductive ink-based fabric piezoresistive tactile sensor to assist clinicians with tissue-retractor interaction force information. The proposed sensor showed a linear relationship with the applied force and has a sensitivity of 0.833 N−1. Finally, cadaver experiments exhibit an effective origami-inspired surgical retractor for assisting surgeons and clinicians in the near future.
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42

Chen, Yi-Ho, and Chao-Chieh Lan. "An Adjustable Constant-Force Mechanism for Adaptive End-Effector Operations." Journal of Mechanical Design 134, no. 3 (February 29, 2012). http://dx.doi.org/10.1115/1.4005865.

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Force regulation is a challenging problem for robot end-effectors when interacting with an unknown environment. It often requires sophisticated sensors with computerized control. This paper presents an adjustable constant-force mechanism (ACFM) to passively regulate the contact force of a robot end-effector. The proposed ACFM combines the negative stiffness of a bistable mechanism and positive stiffness of a linear spring to generate a constant-force output. Through prestressing the linear spring, the constant-force magnitude can be adjusted to adapt to different working environments. The ACFM is a monolithic compliant mechanism that has no frictional wear and is capable of miniaturization. We propose a design formulation to find optimal mechanism configurations that produce the most constant-force. A resulting force to displacement curve and maximal stress curve can be easily manipulated to fit a different application requirement. Illustrated experiments show that an end-effector equipped with the ACFM can adapt to a surface of variable height, without additional motion programming. Since sensors and control effort are minimized, we expect this mechanism can provide a reliable alternative for robot end-effectors to interact friendly with an environment.
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43

She, Yu, Zhaoyuan Gu, Siyang Song, Hai-Jun Su, and Junmin Wang. "Design, Modeling, and Manufacturing of a Variable Lateral Stiffness Arm Via Shape Morphing Mechanisms." Journal of Mechanisms and Robotics 13, no. 3 (March 26, 2021). http://dx.doi.org/10.1115/1.4050379.

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Abstract In this article, we present a continuously tunable stiffness arm for safe physical human–robot interactions. Compliant joints and compliant links are two typical solutions to address safety issues for physical human–robot interactions via introducing mechanical compliance to robotic systems. While extensive studies explore variable stiffness joints/actuators, variable stiffness links for safe physical human–robot interactions are much less studied. This article details the design and modeling of a compliant robotic arm whose stiffness can be continuously tuned via cable-driven mechanisms actuated by a single servo motor. Specifically, a 3D-printed compliant robotic arm is prototyped and tested by static experiments, and an analytical model of the variable stiffness arm is derived and validated by testing. The results show that the lateral stiffness of the robot arm can achieve a variety of 221.26% given a morphing angle of 90 deg. The variable stiffness arm design developed in this study could be a promising approach to address safety concerns for safe physical human–robot interactions.
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44

Attal, Abhishek, and Ashish Dutta. "Design of a variable stiffness index finger exoskeleton." Robotica, August 9, 2021, 1–17. http://dx.doi.org/10.1017/s0263574721000965.

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Abstract This paper presents the design and experimentation of a variable stiffness index finger exoskeleton consisting of four-bar mechanisms actuated by a linear actuator. The lengths of the four-bar mechanism were optimized so that it can follow a recorded index fingertip trajectory. The mechanism has a fixed compliance at the coupler of the four-bar link and a variable compliance at the linear actuator that moves the four-bar. The skeletal shape of the coupler of the finger link has been optimized using FEM. The exoskeleton can apply a constant fingertip force irrespective of the position of the fingers.
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45

Li, Zhongyi, Shaoping Bai, Weihai Chen, and Jianbin Zhang. "Nonlinear Stiffness Analysis of Spring-Loaded Inverted Slider Crank Mechanisms With a Unified Model." Journal of Mechanisms and Robotics 12, no. 3 (February 6, 2020). http://dx.doi.org/10.1115/1.4045649.

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Abstract A mechanism with lumped-compliance can be constructed by mounting springs at joints of an inverted slider crank mechanism. Different mounting schemes bring change in the stiffness performance. In this paper, a unified stiffness model is developed for a comprehensive analysis of the stiffness performance for mechanisms constructed with different spring mounting schemes. With the model, stiffness behaviors of spring-loaded inverted slider crank mechanisms are analyzed. Influences of each individual spring on the overall performance are characterized. The unified stiffness model allows designing mechanisms for a desired stiffness performance, such as constant-torque mechanism and variable stiffness mechanism, both being illustrated with a design example and experiments.
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46

She, Yu, Siyang Song, Hai-Jun Su, and Junmin Wang. "A Comparative Study on the Effect of Mechanical Compliance for a Safe Physical Human–Robot Interaction." Journal of Mechanical Design 142, no. 6 (March 3, 2020). http://dx.doi.org/10.1115/1.4046068.

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Abstract In this paper, we study the effects of mechanical compliance on safety in physical human–robot interaction (pHRI). More specifically, we compare the effect of joint compliance and link compliance on the impact force assuming a contact occurred between a robot and a human head. We first establish pHRI system models that are composed of robot dynamics, an impact contact model, and head dynamics. These models are validated by Simscape simulation. By comparing impact results with a robotic arm made of a compliant link (CL) and compliant joint (CJ), we conclude that the CL design produces a smaller maximum impact force given the same lateral stiffness as well as other physical and geometric parameters. Furthermore, we compare the variable stiffness joint (VSJ) with the variable stiffness link (VSL) for various actuation parameters and design parameters. While decreasing stiffness of CJs cannot effectively reduce the maximum impact force, CL design is more effective in reducing impact force by varying the link stiffness. We conclude that the CL design potentially outperforms the CJ design in addressing safety in pHRI and can be used as a promising alternative solution to address the safety constraints in pHRI.
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47

Jujjavarapu, Sri Sadhan, Amirhossein H. Memar, M. Amin Karami, and Ehsan T. Esfahani. "Variable Stiffness Mechanism for Suppressing Unintended Forces in Physical Human–Robot Interaction." Journal of Mechanisms and Robotics 11, no. 2 (February 27, 2019). http://dx.doi.org/10.1115/1.4042295.

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This paper presents the design of a two-degrees-of-freedom (DoFs) variable stiffness mechanism and demonstrates how its adjustable compliance can enhance the robustness of physical human–robot interaction. Compliance on the grasp handle is achieved by suspending it in between magnets in preloaded repelling configuration to act as nonlinear springs. By adjusting the air gaps between the outer magnets, the stiffness of the mechanism in each direction can be adjusted independently. Moreover, the capability of the proposed design in suppressing unintended interaction forces is evaluated in two different experiments. In the first experiment, improper admittance controller gain leads to unstable interaction, whereas in the second case, high-frequency involuntary forces are caused by the tremor.
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48

Park, Jung-Jun, and Jae-Bok Song. "A Nonlinear Stiffness Safe Joint Mechanism Design for Human Robot Interaction." Journal of Mechanical Design 132, no. 6 (May 25, 2010). http://dx.doi.org/10.1115/1.4001666.

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Service robots used in human environments must be designed to avoid collisions with humans. A safe robot arm can be designed using active or passive compliance methods. A passive compliance system composed of purely mechanical elements often provides faster and more reliable responses for dynamic collision than an active one involving sensors and actuators. Because positioning accuracy and collision safety are equally important, a robot arm should have very low stiffness when subjected to a collision force that could cause human injury but should otherwise maintain very high stiffness. A novel safe joint mechanism (SJM) consisting of linear springs and a double-slider mechanism is proposed to address these requirements. The SJM has variable stiffness that can be achieved with only passive mechanical elements. Analyses and experiments on static and dynamic collisions show high stiffness against an external torque less than a predetermined threshold value and an abrupt drop in stiffness when the external torque exceeds this threshold. The SJM enables the robotic manipulator to guarantee positioning accuracy and collision safety and it is simple to install between an actuator and a robot link without a significant change in the robot’s design.
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49

Yu, Jue, Yong Zhao, Genliang Chen, Yeqing Gu, Chao Wang, and Shunzhou Huang. "Realizing Controllable Physical Interaction Based on an Electromagnetic Variable Stiffness Joint." Journal of Mechanisms and Robotics 11, no. 5 (July 8, 2019). http://dx.doi.org/10.1115/1.4044002.

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This paper puts forward a linear variable stiffness joint (VSJ) based on the electromagnetic principle. The VSJ is constituted by an annular permanent magnet (PM) and coaxial cylindrical coil. The output force and stiffness are linearly proportional to the coil current. In consequence, the stiffness adjustment motor and mechanisms required by many common designs of VSJs are eliminated. A physical prototype of the electromagnetic VSJ is manufactured and tested. The results indicate that the prototype can achieve linear force-deflection characteristics and rapid stiffness variation response. Using an Arduino and H-bridge driver board, the electromagnetic compliance control system is developed in order to realize the precise control of the interaction force. The static force control error is no more than ±0.5 N, and the settling time can be controlled within only 40 ms. At last, an experiment of squeezing the raw egg is conducted. The experiment intuitively exhibits the performance of electromagnetic compliance in stable force control and keeping safe robot-environment interaction.
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50

Han, Sang Min, and Yoon Young Kim. "Topology optimization of linkage mechanisms simultaneously considering both kinematic and compliance characteristics." Journal of Mechanical Design, September 11, 2020, 1–51. http://dx.doi.org/10.1115/1.4048411.

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Abstract Studies on the topology optimization of linkage mechanisms have thus far focused mainly on mechanism synthesis considering only kinematic characteristics describing a desired path or motion. Here, we propose a new topology optimization method that synthesizes a linkage mechanism considering not only kinematic but also compliance (K&C) characteristics simultaneously, as compliance characteristics can also significantly affect the linkage mechanism performance; compliance characteristics dictate how elastic components, such as bushings in a vehicle suspension, are deformed by external forces. To achieve our objective, we use the spring-connected rigid block model (SBM) developed earlier for mechanism synthesis considering only kinematic characteristics, but we make it suitable for the simultaneous consideration of K&C characteristics during mechanism synthesis by making its zero-length springs multifunctional. Variable-stiffness springs were used to identify the mechanism kinematic configuration only, but now in the proposed approach, they serve to determine not only the mechanism kinematic configuration but also the compliance element distribution. In particular, the ground-anchoring springs used to anchor a linkage mechanism to the ground are functionalized to simulate actual bushings as well as to identify the desired linkage kinematic chain. After the proposed formulation and numerical implementation are presented, case studies are considered. In particular, the effectiveness of the proposed method is demonstrated with a simplified two-dimensional vehicle suspension design problem. This study is expected to pave the way to advance the topology optimization method for general linkage mechanisms whenever K&C characteristics must be simultaneously considered for mechanism synthesis.
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