Design of a Compliant Mechanism to Generate an Arbitrary Nonlinear Force-Deflection Profile

2018 ◽  
Author(s):  
Kyle Buschkoetter ◽  
Ashok Midha
Keyword(s):  
Resistance Exercise ◽  
Case Studies ◽  
Compliant Mechanism ◽  
Synthesis Method ◽  
Variable Stiffness ◽  
Variable Resistance ◽  
Wide Range ◽  
Nonlinear Force ◽  
Exercise Equipment ◽  
Variable Stiffness Actuators

This paper presents a compliant mechanism that can generate a wide range of force-deflection profiles. This partially compliant mechanism is comprised of a wedge cam with a compliant follower. The designer specifies the material and geometric properties of the compliant segment, as well as a desired force-deflection profile. A cam surface is then synthesized that helps generate this profile. The synthesis method is validated experimentally with the help of two case studies. Some possible areas of application include robotics, variable stiffness actuators, electrical connectors, design for automotive crashworthiness, and variable resistance exercise equipment.

Selection and implementation of optimal magnetorheological brake design for a variable impedance exoskeleton robot joint

2016 ◽  
Vol 231 (5) ◽  
pp. 941-960 ◽  
Author(s):  
Ozgur Baser ◽  
Mehmet Alper Demiray
Keyword(s):  
Volume Ratio ◽  
Variable Stiffness ◽  
Humanoid Robots ◽  
Performance Comparison ◽  
Analytical Models ◽  
Exoskeleton Robot ◽  
Wide Range ◽  
Braking Torque ◽  
Variable Damping ◽  
Variable Stiffness Actuators

Next-generation exoskeleton and humanoid robots are expected to behave similar to the human neuro-muscular system to perform stable, flexible, and biomimetic movements. To achieve this goal, the variable stiffness actuators have been widely used in various robots. Using variable damping actuators along with variable stiffness actuators will be extremely beneficial for wide range of stable movements. Magnetorheological (MR) brakes are one of the most promising electromagnetic structures that can provide such variable damping in a relatively small actuator volume. In this paper, we focused on the design, characterization, selection and implementation of T-shaped, inner coil and outer coil multi-pole MR brakes to the ankle of an exoskeleton robot. Analytical models are developed using the magnetic circuit analysis to determine the braking torque. Then, magnetic finite element models are developed and coupled with an optimization algorithm to determine the optimal set of parameters of each MR brake design. Prototypes are manufactured in same size and tested experimentally to characterize the actuators’ torque-to-volume ratio, transient response, hysteresis, torque tracking, energy consumption, and damping performances. The performance comparison of the brakes showed T-shaped multi-pole MR brake design has superior characteristics compared to two other designs. Therefore, T-shaped multi-pole MR brake design is coupled with a variable stiffness actuator and implemented in an ankle joint of an exoskeleton robot and experimentally tested. The results show that the developed new hybrid robot joint is capable of stable movement with a simple control algorithm by changing its stiffness and damping independently.

Design of a Variable Stiffness Actuator Based on Flexures

2011 ◽  
Vol 3 (3) ◽  
Author(s):  
Gianluca Palli ◽  
Giovanni Berselli ◽  
Claudio Melchiorri ◽  
Gabriele Vassura
Keyword(s):  
Compliant Mechanism ◽  
Variable Stiffness ◽  
Human Robot Interaction ◽  
Experimental Characterization ◽  
Robot Interaction ◽  
Trade Off ◽  
Variable Stiffness Actuator ◽  
Robotic Devices ◽  
Stiffness Profile ◽  
Variable Stiffness Actuators

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.

Variable Stiffness Mechanism for Tremor Suppression in Human-Robot Interaction

2018 ◽  
Author(s):  
Sri Sadhan Jujjavarapu ◽  
M. Amin Karami ◽  
Ehsan T. Esfahani
Keyword(s):  
Permanent Magnets ◽  
Involuntary Movement ◽  
Cutoff Frequency ◽  
Variable Stiffness ◽  
Rehabilitation Robotics ◽  
Human Robot Interaction ◽  
Limb Stiffness ◽  
Wide Range ◽  
Nonlinear Force ◽  
Human Limb

Variable stiffness mechanisms have a wide range of applications in the field of human-robot interactions such as rehabilitation robotics, prosthesis and industrial robotics due to their ability to comply with the human limb stiffness in an unstructured environment. This paper presents the analysis of a single degree of freedom variable stiffness actuator based on nonlinear force interactions between permanent magnets and its effect on the natural frequency of the system. In the proposed mechanism, variable stiffness is achieved by modifying the separation between magnets. The main goal here is to achieve a desired cutoff frequency by varying the stiffness of the system to filter out the involuntary movement of upper limb during physical human-robot interactions. Moreover, due to the spring-like non-contact force interactions between magnets, this mechanism can prevent the exchange of high impact forces between the robot and human.

scholarly journals A Statically Balanced Shape Shifting Surface

2012 ◽  
Author(s):  
Joseph E. Pishnery ◽  
Craig P. Lusk
Keyword(s):  
Compliant Mechanism ◽  
Tiling Array ◽  
Variable Stiffness ◽  
Parent Material ◽  
Thin Plates ◽  
Physical Barrier ◽  
Zero Force ◽  
Polygonal Cell ◽  
Wide Range ◽  
Macro Scale

This paper presents a concept for producing a Statically Balanced Shape-Shifting Surface (SB-SSS). In this context, an SB-SSS is a surface that can require near-zero magnitude force changes to accomplish a change in shape while retaining effectiveness as a physical barrier. This paper focuses on how to statically balance a specifically-designed compliant mechanism and how to incorporate this mechanism into a polygonal cell. The mechanism consists of a compliant Peaucellier-Lipkin linkage layered with a pre-stressed link as the balancer. Prior art is presented that can show how a polygonal cell can be incorporated into a surface via a tiling array. Specifically shaped overlapping thin plates are used to retain the physical barrier requirement. The demonstration of a virtually zero-force Shape-Shifting Surface (SSS) suggests that SSS’s can be designed with a wide range of force-displacement properties, i.e. ranging from that of a square of the parent material to the zero-force mechanism presented here. Applications for an SB-SSS may be macro-scale or micro-scale and may include sensors, biomedical applications, defense applications, and variable stiffness materials.

scholarly journals A Configurable Architecture for Two Degree-of-Freedom Variable Stiffness Actuators to Match the Compliant Behavior of Human Joints

2021 ◽  
Vol 8 ◽  
Author(s):  
Simon Lemerle ◽  
Manuel G. Catalano ◽  
Antonio Bicchi ◽  
Giorgio Grioli
Keyword(s):  
Variable Stiffness ◽  
Degree Of Freedom ◽  
Design Parameters ◽  
Dimensional Parameter ◽  
Passive Behavior ◽  
Compliant Behavior ◽  
Wide Range ◽  
Articulated Robots ◽  
Variable Stiffness Actuators ◽  
Two Degree Of Freedom

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.

A new variable stiffness robot joint

2015 ◽  
Vol 42 (4) ◽  
pp. 371-378 ◽  
Author(s):  
Yong Tao ◽  
Tianmiao Wang ◽  
Yunqing Wang ◽  
Long Guo ◽  
Hegen Xiong ◽  
...  
Keyword(s):  
Design Methodology ◽  
Dynamic Stiffness ◽  
Variable Stiffness ◽  
System Behavior ◽  
Pivot Point ◽  
Content Type ◽  
Wide Range ◽  
Variable Stiffness Actuators ◽  
Stiffness Adjustment ◽  
Elastic Elements

Purpose – This study aims to propose a new variable stiffness robot joint (VSR-joint) for operating safely. More and more variable stiffness actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user and their ability to store and release energy in passive elastic elements. Design/methodology/approach – The design of VSR-joint is compact and integrated highly and the operating is simply. The mechanics, the principle of operation and the model of the VSR-joint are proposed. The principle of operation of VSR-joint is based on a lever arm mechanism with a continuously regulated pivot point. The VSR-joint features a highly dynamic stiffness adjustment along with a mechanically programmable system behavior. This allows an easy adaption to a big variety of tasks. Findings – Preliminary results are presented to demonstrate the fast stiffness regulation response and the wide range of stiffness achieved by the proposed VSR-joint design. Originality/value – In this paper, a new variable stiffness joint is proposed through changing the cantilever arm to change the performance of the elastic element, which is compact, small size and simple adjustment.

Design of a Monolithic Constant-Force Compliant Mechanism for Extended Range of Motion and Minimal Force Variation

2021 ◽  
Author(s):  
Ching-Wei Lo ◽  
Yuan Chang ◽  
Mien-Li Wang ◽  
Cian-Ru Lin ◽  
Jyh-Jone Lee
Keyword(s):  
Finite Element ◽  
Range Of Motion ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Synthesis Method ◽  
Structural Deformation ◽  
Constant Force ◽  
Wide Range ◽  
Extended Range ◽  
Force Variation

Abstract Compliant mechanisms enable passive force control through induction of strain energy during deformation. This has been perceived as a desired factor for developing precise handling equipment of limited size where additional sensors and controls are inessential to its operation. In this paper, our objective is to design a monolithic constant-force compliant mechanism to be integrated in a constant-force gripper for extended range of bidirectional motion. A topology synthesis method has been proposed by means of domain definition, discrete parameterization, topology optimization, and nonlinear structural deformation evaluation. This article adapts a compliant topology of a homogeneous beam configuration that exhibits zero stiffness behavior over a pre-established effective region. The optimization by genetic algorithm generates discrete shaping parameters for formation of an optimal geometry. The structural deformation computation via vector form intrinsic finite element that accounts for large displacement motion quantifies an iterative series of load-displacement relations in the optimization. Results have been verified using a conventional finite element method. A conceptual gripper has been proposed with a pair of embedded constant-force compliant mechanisms. This procedure has prepared a general guideline for future development of passive compliant devices that require accurate force regulation over a wide range of motion.

Design and Implementation of a Novel Variable Stiffness Actuator with Cam-Based Relocation Mechanism

2020 ◽  
pp. 1-22
Author(s):  
Yinghao Ning ◽  
Hailin Huang ◽  
Wenfu Xu ◽  
Weimin Zhang ◽  
Bing Li
Keyword(s):  
Variable Stiffness ◽  
Human Robot Interaction ◽  
Tracking Accuracy ◽  
Robot Interaction ◽  
Wide Range ◽  
Lever Mechanism ◽  
Point Control ◽  
Point To Point ◽  
Safe Performance ◽  
Variable Stiffness Actuators

Abstract Variable stiffness actuators (VSAs) are widely explored as they could improve the safe performance for human-robot interaction and make the system torque controllable based on the internal compliance. This paper presents a novel VSA based on the cam-based relocation mechanism (CRM-VSA), which is utilized to change the locations of pivot and spring of a lever mechanism simultaneously. Consequently, such structure makes the actuator compacted and the stiffness regulation designable which could help engineers to pursue different demands of stiffness regulation. The simultaneous relocations of the pivot and spring also permit a wide range of adjustable stiffness. By introducing linear guide pairs, the internal friction of the relocations of pivot and spring could be greatly reduced, thus enhancing the energy efficiency. To evaluate the performance of the proposed CRM-VSA, the point-to-point control strategy is developed which contributes to a higher tracking accuracy and oscillation attenuation at both the start and end points of the trajectory. Additionally, the performance of torque controllability is also verified through experiments. These excellent capabilities enable the proposed CRM-VSA to be qualified for constructing a robotic arm towards service applications.

Myths of the Underworld in Contemporary Culture

2019 ◽  
Author(s):  
Judith Fletcher
Keyword(s):  
Short Stories ◽  
Case Studies ◽  
Joseph Conrad ◽  
Ezra Pound ◽  
Border Crossing ◽  
First Century ◽  
Contemporary Culture ◽  
Cinematic Adaptation ◽  
Narrative Tradition ◽  
Wide Range

Stories of a visit to the realm of the dead and a return to the upper world are among the oldest narratives in European literature, beginning with Homer’s Odyssey and extending to contemporary culture. This volume examines a series of fictional works by twentieth- and twenty-first century authors, such Toni Morrison and Elena Ferrante, which deal in various ways with the descent to Hades. Myths of the Underworld in Contemporary Culture surveys a wide range of genres, including novels, short stories, comics, a cinematic adaptation, poetry, and juvenile fiction. It examines not only those texts that feature a literal catabasis, such as Neil Gaiman’s Sandman series, but also those where the descent to the underworld is evoked in more metaphorical ways as a kind of border crossing, for instance Salman Rushdie’s use of the Orpheus myth to signify the trauma of migration. The analyses examine how these retellings relate to earlier versions of the mythical theme, including their ancient precedents by Homer and Vergil, but also to post-classical receptions of underworld narratives by authors such as Dante, Ezra Pound, and Joseph Conrad. Arguing that the underworld has come to connote a cultural archive of narrative tradition, the book offers a series of case studies that examine the adaptation of underworld myths in contemporary culture in relation to the discourses of postmodernism, feminism, and postcolonialism.

Explanation Beyond Causation

2018 ◽  
Keyword(s):  
Philosophy Of Science ◽  
Case Studies ◽  
Philosophical Study ◽  
Accurate Information ◽  
Contemporary Philosophy ◽  
Causal Information ◽  
Causal Explanations ◽  
Turn On ◽  
Detailed Case ◽  
Wide Range

Explanations are very important to us in many contexts: in science, mathematics, philosophy, and also in everyday and juridical contexts. But what is an explanation? In the philosophical study of explanation, there is long-standing, influential tradition that links explanation intimately to causation: we often explain by providing accurate information about the causes of the phenomenon to be explained. Such causal accounts have been the received view of the nature of explanation, particularly in philosophy of science, since the 1980s. However, philosophers have recently begun to break with this causal tradition by shifting their focus to kinds of explanation that do not turn on causal information. The increasing recognition of the importance of such non-causal explanations in the sciences and elsewhere raises pressing questions for philosophers of explanation. What is the nature of non-causal explanations—and which theory best captures it? How do non-causal explanations relate to causal ones? How are non-causal explanations in the sciences related to those in mathematics and metaphysics? This volume of new essays explores answers to these and other questions at the heart of contemporary philosophy of explanation. The essays address these questions from a variety of perspectives, including general accounts of non-causal and causal explanations, as well as a wide range of detailed case studies of non-causal explanations from the sciences, mathematics and metaphysics.

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