Lamina Emergent Torsional Joints Research Articles

Quadristability achieved by torsion-bending antagonistic action in a lamina emergent torsional joint

Multistability is the characteristic of a device can steadily stay at two or more positions without external power input, which has been employed to design surgical tools, mechanical metamaterials, logic operators, and multi-configuration robots. However, most existing multistable mechanisms with three or more stable states are created by combining several bistable mechanism units in series or parallel. This work proposes a novel quadristable compliant mechanism that achieves quadristablity utilizing the antagonistic action between torsional deflection and bending deflection in a lamina emergent torsional joint, rather than combining several bistable mechanism units. A kinetostatic model is developed based on the chained power series model to capture the load-deflection relations of this quadristable mechanism. Six design examples are presented to explore the quadristable characteristics using the kinetostatic model and nonlinear finite element model. The results are verified by the experimental results of several prototypes with varying structural parameters. The diverse stable shapes could also be useful for shape morphing mechanical metamaterials.

A Torsion-Bending Antagonistic Bistable Actuator Enables Untethered Crawling and Swimming of Miniature Robots.

Miniature robots show great potential in exploring narrow and confined spaces to perform various tasks, but many applications are limited by the dependence of these robots on electrical or pneumatic tethers to power supplies outboard. Developing an onboard actuator that is small in size and powerful enough to carry all the components onboard is a major challenge to eliminate the need for a tether. Bistability can trigger a dramatic energy release during switching between the 2 stable states, thus providing a promising way to overcome the intrinsic limitation of insufficient power of small actuators. In this work, the antagonistic action between torsional deflection and bending deflection in a lamina emergent torsional joint is utilized to achieve bistability, yielding a buckling-free bistable design. The unique configuration of this bistable design enables integrating of a single bending electroactive artificial muscle in the structure to form a compact, self-switching bistable actuator. A low-voltage ionic polymer-metal composites artificial muscle is employed, yielding a bistable actuator capable of generating an instantaneous angular velocity exceeding 300 °/s by a 3.75-V voltage. Two untethered robotic demonstrations using the bistable actuator are presented, including a crawling robot (gross weight of 2.7 g, including actuator, battery, and on-board circuit) that can generate a maximum instantaneous velocity of 40 mm/s and a swimming robot equipped with a pair of origami-inspired paddles that swims breaststroke. The low-voltage bistable actuator shows potential for achieving autonomous motion of various fully untethered miniature robots.

Design and Performance Analysis of Lamina Emergent Torsional Joints Based on Double-Laminated Material Structure

Flexibility and accuracy are two key aspects of the performances of compliant joints. In order to obtain high flexibility while maintain high accuracy, this paper proposes a design method to improve the tensile stiffness of Lamina Emergent Torsional (LET) joint by utilizing double-laminated material structure. The joint is made of a LET joint and a layer of flexible H18 aluminum foil fixing on it (called double-laminated LET, DL-LET). The kinetostatic model for the joint is given, and the equations needed to calculate the equivalent spring constant are derived. The model is verified using finite element analysis (FEA). The results obtained through two different ways coincide with each other very well. The results show that DL-LET and LET joints have similar bending stiffness, while the tensile stiffness of the DL-LET joint is much larger than that of the LET joint. The results are validated by tensile tests. Finally, to further demonstrate the extension of this idea, a DL-Triple-LET joint is presented and compared to the Triple-LET joint.

Hinges and Curved Lamina Emergent Torsional Joints in Cylindrical Developable Mechanisms

Abstract Cylindrical developable mechanisms are devices that conform to and emerge from a cylindrical surface. These mechanisms can be formed or cut from the cylinder wall itself. This paper presents a study on adapting traditional hinge options to achieve revolute motion in these mechanisms. A brief overview of options is given, including classical pin hinges, small-length flexural pivots, initially curved beams, and an adaptation of the membrane thickness-accommodation technique. Curved lamina emergent torsional (LET) joints are then evaluated in detail, and a thin-walled modeling assumption is checked analytically and empirically. A small-scale cylindrical developable mechanism is then evaluated with Nitinol curved LET joints.

Regional Stiffness Reduction Using Lamina Emergent Torsional Joints for Flexible Printed Circuit Board Design

Flexible printed circuit boards (PCBs) make it possible for engineers to design devices that use space efficiently and can undergo changes in shape and configuration. However, they also suffer from tradeoffs due to nonideal material properties. Here, a method is presented that allows engineers to introduce regions of flexibility in otherwise rigid PCB substrates. This method employs geometric features to reduce local stiffness in the PCB, rather than reducing the global stiffness by material selection. Analytical and finite element models are presented to calculate the maximum stresses caused by deflection. An example device is produced and tested to verify the models.

Membrane-Enhanced Lamina Emergent Torsional Joints for Surrogate Folds

Lamina emergent compliant mechanisms (including origami-adapted compliant mechanisms) are mechanical devices that can be fabricated from a planar material (a lamina) and have motion that emerges out of the fabrication plane. Lamina emergent compliant mechanisms often exhibit undesirable parasitic motions due to the planar fabrication constraint. This work introduces a type of lamina emergent torsion (LET) joint that reduces parasitic motions of lamina emergent mechanisms, and presents equations for modeling parasitic motion of LET joints. The membrane joint also makes possible one-way joints that can ensure origami-based mechanisms emerge from their flat state (a change point) into the desired configuration. Membrane-enhanced LET (M-LET) joints, including one-way surrogate folds, are described here and show promise for use in a wide range of compliant mechanisms and origami-based compliant mechanisms. They are demonstrated as individual joints and in mechanisms such as a kaleidocycle (a 6R Bricard linkage), degree-4 origami vertices (spherical mechanisms), and waterbomb base mechanisms (an 8R multi-degrees-of-freedom origami-based mechanism).

Symmetric Equations for Evaluating Maximum Torsion Stress of Rectangular Beams in Compliant Mechanisms

There are several design equations available for calculating the torsional compliance and the maximum torsion stress of a rectangular cross-section beam, but most depend on the relative magnitude of the two dimensions of the cross-section (i.e., the thickness and the width). After reviewing the available equations, two thickness-to-width ratio independent equations that are symmetric with respect to the two dimensions are obtained for evaluating the maximum torsion stress of rectangular cross-section beams. Based on the resulting equations, outside lamina emergent torsional joints are analyzed and some useful design insights are obtained. These equations, together with the previous work on symmetric equations for calculating torsional compliance, provide a convenient and effective way for designing and optimizing torsional beams in compliant mechanisms.