Design and Characterization of a Continuous Rotary Minimotor Based on Shape Memory Wires and Overrunning Clutches
An attractive but little explored field of application of the shape memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on shape memory alloy (SMA) wires and overrunning clutches which produces high output torque and unlimited rotation. The concept features a SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contraction-elongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process formerly developed by the authors, a six-stage prototype with size envelope of 48´22´30 mm is built and tested. Diverse supply strategies are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31´10-4 Nmm/mm3; rotation per module = 15 deg/cycle; free continuous speed = 4.4 rpm.
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The synthesis of functional molecular mechanisms is constrained by the notorious difficulties in fabricating nano-links of prescribed shapes and sizes. Thus, the classical mechanism synthesis methods, which assume the ability to manufacture any designed links, cannot provide a systematic process for designing molecular mechanisms. We propose a new approach to build functional mechanisms with prescribed mobility by only using elements from a predefined "link soup". The resulting synthesis procedure is the first of its kind that is capable of systematically synthesizing functional linkages with prescribed mobility constructed from a soup of primitive entities. Furthermore, the proposed systematic approach outputs the ATLAS of candidate mechanisms, which can be further processed for downstream applications. Although the scope of this technique is rather general, its immediate application is the design of molecular machines assembled from nano-links that either exist in nature or can be fabricated.
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Toward a Unified Design Approach for Both Compliant Mechanisms and Rigid-Body Mechanisms: Module Optimization
Lin Cao, Allan T. Dolovich, Arend L. Schwab, Just L. Herder and Wenjun (Chris) ZhangJ. Mech. Des 137(12), 122301; doi: 10.1115/1.4031294
Rigid-body mechanisms (RBMs) and compliant mechanisms (CMs) are traditionally treated in significantly different ways. In this paper, we present an approach to the synthesis of both RBMs and CMs. In this approach, RBMs and CMs are generalized into mechanisms that consist of five basic modules, including Compliant Link (CL), Rigid Link (RL), Pin Joint (PJ), Compliant Joint (CJ), and Rigid Joint (RJ). The link modules and joint modules are modeled with beam and hinge elements, respectively, in a geometrically nonlinear finite element solver, and subsequently a discrete beam-hinge ground structure model is established. Based on this discrete beam-hinge model, a procedure that follows topology optimization is developed, called module optimization. Particularly, in the module optimization approach, the states (both presence or absence and sizes) of joints and links are all design variables, and one may obtain a RBM, a partially CM, or a fully CM for a given mechanical task. The proposed approach has thus successfully addressed the challenge in the type and dimensional synthesis of RBMs and CMs. Three design examples of the path generator are discussed to demonstrate the effectiveness of the proposed approach.
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We have developed an improved deformable Underconstraint Eliminator (UE) linkage for removing underconstraint, which causes unwanted resonances and reduced stiffness at large displacements, in linear flexure bearings. Linear flexure bearings deform to permit high repeatability, fine resolution translational motion. This new linkage alleviates many of the problems associated with current linkage solutions such as static and dynamic performance losses and increased bearing size. The nested linkage design is shown through analysis and experiment to work as predicted in selectively eliminating the underconstrained degrees of freedom (DOF) in linear flexure bearings. The improved bearing shows a >10x gain in the resonance frequency and >100x gain in static stiffness of the underconstrained DOF, as designed. Analytical expressions are presented for designers to calculate the performance of the new UE linkage. The linear nested linkage concept is also generalized to a rotary flexure design.
Fig. 1. a) Flexure bearing with the new nested underconstraint eliminator (UE) linkage. This linkage selectively removes the underconstraint inherent in the bearing design by linking the motion of the intermediate and final stage. b) Schematic of the UE linkage, this is the triangular structure in the center, enabled by flexures (11, 12, and 2), which does not impede the motion of the bearing flexures (m). The possible motion for the structure is shown in the equivalent linkage model in c).
Authors: Matteo Verotti; Rocco Crescenzi; Marco Balucani; Nicola P. Belfiore
J. Mech. Des.. 137(1), 012301 (2015); doi:10.1115/1.4028791
Compliant mechanisms may change their configuration thanks to their flexible parts, generally called flexures. They present some significant advantages with respect to rigid body mechanisms: no backlash and friction, no need for lubrication and maintenance reduction, and, mainly, the possibility of being crafted by means of planar construction technology, as a unique block of material. For this reason, MEMS can be developed by using the same principles adopted for the design of compliant mechanisms.
However, flexures are characterized by some disadvantages, such as limited capability in terms of motion and force transmission, deformations highly dependent on the applied loads, limited resistance to yielding, variable position of the center of relative rotation.
In this paper, a new flexure hinge is introduced, with the aim of overcoming some of such limitations. The Conjugate Surfaces Flexure Hinge (CSFH) combines a curved beam, as flexible element, and a pair of conjugate surfaces, whose contact depends upon the load conditions. The contact between the conjugate surfaces can reduce the stress in the curved beam and limit the variations of the position of the relative rotations center.
This paper discloses how to simulate (both theoretically and with finite element analysis), construct (by means of a single step lithography and Reactive–Ion Etching, RIE), process and test (by means of in-SEM observation and manipulation) a new concept silicon CSFH prototype.
Conjugate Surfaces Flexure Hinge for MEMS applications (geometric layout (a) and test of the silicon prototype (b)) and for macro scale applications (geometric layout (c) and PVC prototype in neutral and deformed configurations (d)).
This section includes brief descriptions of articles soon to be or recently published by the Journal of Mechanical Design. These featured articles highlight recent research developments and emerging trends in mechanical design. For Abstracts and Full Articles please see ASME's Digital Collection.