scholarly journals Microinjection Molding of Out-of-Plane Bistable Mechanisms

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 155 ◽  
Author(s):  
Wook-Bae Kim ◽  
Sol-Yi Han
Keyword(s):  
Mold Insert ◽  
Displacement Curve ◽  
Beam Structure ◽  
Buckling Mode ◽  
Microinjection Molding ◽  
Shape Morphing ◽  
Out Of Plane ◽  
Mold Fabrication ◽  
Bistable Mechanism ◽  
Dimensional Errors

We present a novel fabrication technique of a miniaturized out-of-plane compliant bistable mechanism (OBM) by microinjection molding (MM) and assembling. OBMs are mostly in-plane monolithic devices containing delicate elastic elements fabricated in metal, plastic, or by a microelectromechanical system (MEMS) process. The proposed technique is based on stacking two out-of-plane V-beam structures obtained by mold fabrication and MM of thermoplastic polyacetal resin (POM) and joining their centers and outer frames to construct a double V-beam structure. A copper alloy mold insert was machined with the sectional dimensions of the V-beam cavities. Next, the insert was re-machined to reduce dimensional errors caused by part shrinkage. The V-beam structure was injection-molded at a high temperature. Gradually elongated short-shots were obtained by increasing pressure, showing the symmetrical melt filling through the V-beam cavities. The as-molded structure was buckled elastically by an external-force load but showed a monostable behavior because of a higher unconstrained buckling mode. The double V-beam device assembled with two single-molded structures shows clear bistability. The experimental force-displacement curve of the molded structure is presented for examination. This work can potentially contribute to the fabrication of architected materials with periodic assembly of the plastic bistable mechanism for diverse functionalities, such as energy absorption and shape morphing.

Mechanism of the Transition From In-Plane Buckling to Helical Buckling for a Stiff Nanowire on an Elastomeric Substrate

2016 ◽  
Vol 83 (4) ◽  
Author(s):  
Youlong Chen ◽  
Yong Zhu ◽  
Xi Chen ◽  
Yilun Liu
Keyword(s):  
High Performance ◽  
Three Dimensional ◽  
Stretchable Electronics ◽  
Buckling Mode ◽  
Design And Optimization ◽  
Out Of Plane ◽  
Plane Direction ◽  
Plane Displacement ◽  
Helical Buckling ◽  
Selection Of

In this work, the compressive buckling of a nanowire partially bonded to an elastomeric substrate is studied via finite-element method (FEM) simulations and experiments. The buckling profile of the nanowire can be divided into three regimes, i.e., the in-plane buckling, the disordered buckling in the out-of-plane direction, and the helical buckling, depending on the constraint density between the nanowire and the substrate. The selection of the buckling mode depends on the ratio d/h, where d is the distance between adjacent constraint points and h is the helical buckling spacing of a perfectly bonded nanowire. For d/h > 0.5, buckling is in-plane with wavelength λ = 2d. For 0.27 < d/h < 0.5, buckling is disordered with irregular out-of-plane displacement. While, for d/h < 0.27, buckling is helical and the buckling spacing gradually approaches to the theoretical value of a perfectly bonded nanowire. Generally, the in-plane buckling induces smaller strain in the nanowire, but consumes the largest space. Whereas the helical mode induces moderate strain in the nanowire, but takes the smallest space. The study may shed useful insights on the design and optimization of high-performance stretchable electronics and three-dimensional complex nanostructures.

An Exploration of Buckling Modes and Deflection of a Fixed-Guided Beam

2010 ◽  
Author(s):  
Gregory L. Holst ◽  
Gregory H. Teichert ◽  
Brian D. Jensen
Keyword(s):  
Elliptic Integral ◽  
Large Deflections ◽  
Buckling Mode ◽  
Beam Shape ◽  
Buckling Modes ◽  
Buckling Behavior ◽  
Reaction Forces ◽  
Combined Models ◽  
Beam Bending ◽  
Bistable Mechanism

This paper explored the deflection and buckling of fixed-guided beams. It uses an analytical model for predicting the reaction forces, moments, and buckling modes of a fixed-guided beam undergoing large deflections. One of the strengths of the model is its ability to accurately predict buckling behavior and the buckled beam shape. The model for the bending behavior of the beam is found using elliptic integrals. A model for the axial deflection of the buckling beam is also developed based on the equations for stress and strain and the buckling profile of the beam calculated with the elliptic integral solution. These two models are combined to predict the performance of a beam undergoing large deflections including higher order buckling modes. The force vs. displacement predictions of the model are compared to the experimental force vs. deflection data of a bistable mechanism and a thermomechanical in-plane microactuator (TIM). The combined models show good agreement with the force vs. deflection data for each device. The paper’s main contributions include the addition of the axial buckling model to existing beam bending models, the exploration of the deflection domain of a fixed-guided beam, and the demonstration that nonlinear finite element models may incorrectly predict a beam’s buckling mode unless unrealistic constraints are placed on the beam.

Modeling and Experiments of Buckling Modes and Deflection of Fixed-Guided Beams in Compliant Mechanisms

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Gregory L. Holst ◽  
Gregory H. Teichert ◽  
Brian D. Jensen
Keyword(s):  
Compliant Mechanisms ◽  
Large Deflections ◽  
Buckling Mode ◽  
Buckling Modes ◽  
Reaction Forces ◽  
Combined Models ◽  
Modeling And Experiments ◽  
Beam Bending ◽  
Bending Behavior ◽  
Bistable Mechanism

This paper explores the deflection and buckling of fixed-guided beams used in compliant mechanisms. The paper’s main contributions include the addition of an axial deflection model to existing beam bending models, the exploration of the deflection domain of a fixed-guided beam, and the demonstration that nonlinear finite element models typically incorrectly predict a beam’s buckling mode unless unrealistic constraints are placed on the beam. It uses an analytical model for predicting the reaction forces, moments, and buckling modes of a fixed-guided beam undergoing large deflections. The model for the bending behavior of the beam is found using elliptic integrals. A model for the axial deflection of the buckling beam is also developed. These two models are combined to predict the performance of a beam undergoing large deflections including higher order buckling modes. The force versus displacement predictions of the model are compared to the experimental force versus deflection data of a bistable mechanism and a thermomechanical in-plane microactuator (TIM). The combined models show good agreement with the force versus deflection data for each device.

Experimental Investigation of the Mold Surface Roughness Effect in Microinjection Molding

2011 ◽  
Vol 138-139 ◽  
pp. 1258-1262 ◽  
Author(s):  
Can Yang ◽  
Xiao Hong Yin ◽  
Jose M. Castro ◽  
Allen Y. Yi
Keyword(s):  
Surface Roughness ◽  
Mold Insert ◽  
Injection Velocity ◽  
Mold Surface ◽  
Melt Temperature ◽  
Microinjection Molding ◽  
Diamond Machining ◽  
Trapped Air ◽  
Injection Process ◽  
Effect Of Surface

Microinjection molding has been drawing more and more attention due to its great advantages such as cost effectiveness and mass production capability. In this work, an experimental study was carried out in order to investigate the effect of the mold surface roughness on the achieved filled length of the molded microfeatures. For this purpose, an aluminum mold insert with microchannels having different surface roughness values was designed and fabricated using ultraprecision diamond machining and micromilling method. The experimental results revealed that increasing surface roughness of the microchannel wall led to a decrease in the filled length of the molded microfeatures. It was also found that with increased melt temperature or injection velocity, the effect of surface roughness was weakened by high-pressure trapped air inside the microchannels during injection process. Finally, the influence mechanism of the mold surface roughness was discussed.

Design and Testing of a Thin-Flexure Bistable Mechanism Suitable for Stamping From Metal Sheets

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Benjamin Todd ◽  
Brian D. Jensen ◽  
Stephen M. Schultz ◽  
Aaron R. Hawkins
Keyword(s):  
Compliant Mechanisms ◽  
Elliptic Integral ◽  
Plane Motion ◽  
Acceleration Threshold ◽  
Metal Sheets ◽  
Out Of Plane ◽  
A New Technique ◽  
Bistable Mechanism ◽  
Force Displacement ◽  
Design And Testing

We present a new technique for fabricating compliant mechanisms from stamped metal sheets. The concept works by providing thinned segments to allow rotation of flexural beams 90 deg about their long axis, effectively providing a flexure as wide as the sheet’s thickness. The method is demonstrated with the design and fabrication of a metal bistable mechanism for use as a threshold accelerometer. A new model based on elliptic integral solutions is presented for bistable mechanisms incorporating long, thin flexures. The resulting metal bistable mechanisms are tested for acceleration threshold sensing using a drop test and a vibration test. The mechanisms demonstrate very little variation due to stress relaxation or temperature effects. The force-displacement behavior of a mechanism is also measured. The mechanisms’ switching force is less than the designed value because of out-of-plane motion and dynamic effects.

A Fully-Compliant, In-Plane Rotary, Bistable Micromechanism

2005 ◽  
Author(s):  
Rajesh Luharuka ◽  
Peter J. Hesketh
Keyword(s):  
Aspect Ratio ◽  
Element Model ◽  
Relative Advantage ◽  
Test Results ◽  
Positive Photoresist ◽  
Out Of Plane ◽  
Symmetric Geometry ◽  
Optical Shutter ◽  
Bistable Mechanism ◽  
The Individual

A fully compliant bistable micromechanism (hereafter identified as an in-plane rotary bistable micromechanism or IPRBM) is designed to accomplish in-plane rotary motion with two stable positions. The micromechanism consists of four individually bistable mechanisms arranged in a cyclically symmetric geometry about a central proof mass. This class of bistable mechanism can be used in gate valve, optical shutter, and other switching applications. Two classes of IPRBMs are investigated in this paper. The bistable micromechanism size is less than 1 mm and fabricated by electroplating a soft magnetic material — Permalloy (80% Ni, 20% Fe) in a positive photoresist mold. Minimum feature size in the IPRBM, which corresponds to the width of flexible linkages, is 4 μm. The fabricated IPRBMs have been tested for their force-deflection response using an image based force sensing method. The test results were then compared with the simulated results obtained from a finite element model of the IPRBM. The IPRBM are shown to reversibly undergo 10 to 20 degrees of in-plane rotation and required a maximum torque of 1 to 2 μNm depending on the design. The experimental results showed good overall agreement with the design. A comparison within and between the two classes of IPRBM have been completed for three different design cases between which the tether width and aspect ratio was varied. The study showed a relative advantage of slender tethers with high aspect ratio in minimizing out-of-plane deflection. Also, the radial separation of the individual bistable mechanisms is important.

Shape-Morphing Using Bistable Triangles With Dwell-Enhanced Stability

2018 ◽  
Author(s):  
Rami Alfattani ◽  
Craig Lusk
Keyword(s):  
Compliant Mechanism ◽  
Isosceles Triangle ◽  
Vertex Angle ◽  
The Novel ◽  
Shape Morphing ◽  
Compliant Joints ◽  
Cube Corner ◽  
The Stability ◽  
Bistable Mechanism ◽  
Novel Design

This paper presents a new design concept for a morphing triangle-shaped compliant mechanism. The novel design is a bistable mechanism that has one changeable side. These morphing triangles may be arrayed to create shapemorphing structures. The mechanism was based on a six-bar dwell mechanism that can fit in a triangle shape and has stable positions at the motion-limit (dead-center) positions. An example of the triangle-shaped compliant mechanism was designed and prototyped: an isosceles triangle with a vertex that changes from 120 degrees to 90 degrees and vice versa. Three of these in the 120-degree configuration lie flat and when actuated to the 90-degree configuration become a cube corner. This design may be of use for folding and packaging assistance. The force analysis and the potential energy analysis were completed to verify the stability of the triangle-shaped compliant mechanism. Because of its dead-center motion limits the vertex angle cannot be extended past the range of 90 degrees to 120 degrees in spite of the mechanism’s compliant joints. Furthermore, because it is a dwell mechanism, the vertex angle is almost immobile near its stable configurations, although other links in the mechanism move. This makes the stable positions of the vertex angle robust against stress relaxation and manufacturing errors. We believe this is the first demonstration of this kind of robustness in bistable mechanisms.

Robotic surfaces with reversible, spatiotemporal control for shape morphing and object manipulation

2021 ◽  
Vol 6 (53) ◽  
pp. eabf5116
Author(s):  
Ke Liu ◽  
Felix Hacker ◽  
Chiara Daraio
Keyword(s):  
Stimuli Responsive ◽  
Mechanical Stiffness ◽  
Responsive Materials ◽  
Shape Morphing ◽  
Deformation Response ◽  
Control Scheme ◽  
Out Of Plane ◽  
Passive Network ◽  
Liquid Crystal Elastomers ◽  
Layered Design

Continuous and controlled shape morphing is essential for soft machines to conform, grasp, and move while interacting safely with their surroundings. Shape morphing can be achieved with two-dimensional (2D) sheets that reconfigure into target 3D geometries, for example, using stimuli-responsive materials. However, most existing solutions lack the ability to reprogram their shape, face limitations on attainable geometries, or have insufficient mechanical stiffness to manipulate objects. Here, we develop a soft, robotic surface that allows for large, reprogrammable, and pliable shape morphing into smooth 3D geometries. The robotic surface consists of a layered design composed of two active networks serving as artificial muscles, one passive network serving as a skeleton, and cover scales serving as an artificial skin. The active network consists of a grid of strips made of heat-responsive liquid crystal elastomers (LCEs) containing stretchable heating coils. The magnitude and speed of contraction of the LCEs can be controlled by varying the input electric currents. The 1D contraction of the LCE strips activates in-plane and out-of-plane deformations; these deformations are both necessary to transform a flat surface into arbitrary 3D geometries. We characterize the fundamental deformation response of the layers and derive a control scheme for actuation. We demonstrate that the robotic surface provides sufficient mechanical stiffness and stability to manipulate other objects. This approach has potential to address the needs of a range of applications beyond shape changes, such as human-robot interactions and reconfigurable electronics.

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