Academic literature on the topic 'Bi-stable tape spring'

The first time I read Hélène Cixous’s The Laugh of the Medusa I swooned. I wanted to write the whole thing out, large, and black, and pin it across an entire wall. I was 32 and vulnerable around polemic texts (I was always copying out quotes and sticking them to my walls, trying to hold onto meaning, unable to let the writing I read slip out and away). You must "write your self, your body must be heard" (Cixous 880), I read, as if for the hundredth time, even though it was the first. Those decades old words had an echoing, a resonance to them, as if each person who had read them had left their own mnemonic mark there, so that by the time they reached me, they struck, immediately, at my core (not the heart or the spine, or even the gut, but somewhere stickier; some pulsing place in amongst my organs, somewhere not touched, a space forgotten). The body that read The Laugh was so big its knees had trouble lifting it from chairs (“more body, hence more writing”, Cixous 886), and was soon to have its gallbladder taken. Its polycystic ovaries dreamed, lumpily and without much hope, of zygotes. The body that read The Laugh was a wobbling thing, sheathed in fat (as if this could protect it), with a yearning for sveltness, for muscle, for strength. Cixous sang through its cells, and called it to itself. The body that read The Laugh wrote itself back. It spoke about dungeons, and walls that had collected teenaged fists, and needles that turned it somnambulant and concave and warm until it was not. It wrote trauma in short and staggering sentences (out, get it out) as if narrative could save it from a fat-laden and static decline. Text leaked from tissue and bone, out through fingers and onto the page, and in increments so small I did not notice them, the body took its place. I was, all-of-a-sudden, more than my head. And then the body that read The Laugh performed the ultimate coup, and conceived.The body wrote then about its own birth, and the birth of its mother, and when its own children were born, of course, of course, about them. “Oral drive, anal drive, vocal drive–all these drives are our strengths, and among them is the gestation drive–all just like the desire to write: a desire to live self from within, a desire for the swollen belly, for language, for blood” (Cixous 891). The fat was gone, and in its place this other tissue, that later would be he. What I know now is that the body gets what the body wants. What I know now is that the body will tell its story, because if you “censor the body [… then] you censor breath and speech at the same time” (Cixous 880).I am trying to find a beginning. Because where is the place where I start? I was never a twinkle in my mother’s eye. It was the seventies. She was 22 and then 23–there was nothing planned about me. Her eyes a flinty green, hair long and straight. When I think of her then I remember this photo: black and white on the thick photo paper that is hard to get now. No shiny oblong spat from a machine, this paper was pulled in and out of three chemical trays and hung, dripping, in a dark red room to show me a woman in a long white t-shirt and nothing else. She stares straight out at me. On the shirt is a women’s symbol with a fist in the middle of it. Do you know the one? It might have been purple (the symbol I mean). When I think of her then I see her David Bowie teeth, the ones she hated, and a packet of Drum tobacco with Tally-Hos tucked inside, and some of the scars on her forearms, but not all of them, not yet. I can imagine her pregnant with me, the slow gait, that fleshy weight dragging at her spine and pelvis. She told me the story of my birth every year on my birthday. She remembers what day of the week the contractions started. The story is told with a kind of glory in the detail, with a relishing of small facts. I do the same with my children now. I was delivered by forceps. The dent in my skull, up above my right ear, was a party trick when I was a teenager, and an annoyance when I wanted to shave my head down to the bone at 18. Just before Jem was born, I discovered a second dent behind my left ear. My skull holds the footprint of those silver clamps. My bones say here, and here, this is where I was pulled from you. I have seen babies being born this way. They don’t slide out all sealish and purple and slippy. They are pulled. The person holding the forcep handles uses their whole body weight to yank that baby out. It makes me squirm, all that pulling, those tiny neck bones concertinaing out, the silver scoops sinking into the skull and leaving prints, like a warm spoon in dough. The urgency of separation, of the need to make two things from one. After Jem was born he lay on my chest for hours. As the placenta was birthed he weed on me. I felt the warm trickle down my side and was glad. There was nothing so right as my naked body making a bed for his. I lay in a pool of wet (blood and lichor and Jem’s little wee) and the midwives pushed towels under me so I wouldn’t get cold. He sucked. White waffle weave blankets over both of us. That bloody nest. I lay in it and rested my free hand on his vernix covered back; the softest thing I had ever touched. We basked in the warm wet. We basked. How do I sew theory into this writing? Julia Kristeva especially, whose Stabat Mater describes those early moments of holding the one who was inside and then out so perfectly that I am left silent. The smell of milk, dew-drenched greenery, sour and clear, a memory of wind, of air, of seaweed (as if a body lived without waste): it glides under my skin, not stopping at the mouth or nose but caressing my veins, and stripping the skin from the bones fills me like a balloon full of ozone and I plant my feet firmly on the ground in order to carry him, safe, stable, unuprootable, while he dances in my neck, floats with my hair, looks right and left for a soft shoulder, “slips on the breast, swingles, silver vivid blossom of my belly” and finally flies up from my navel in his dream, borne by my hands. My son (Kristeva, Stabat Mater 141). Is theory more important than this? The smell of milk (dried, it is soursweet and will draw any baby to you, nuzzling and mewling), which resides alongside the Virgin Mother and the semiotics of milk and tears. The language of fluid. While the rest of this writing, the stories not of mothers and babies, but one mother and one baby, came out smooth and fast, as soon as I see or hear or write that word, theory, I slow. I am concerned with the placement of things. I do not have the sense of being free. But if there’s anything that should come from this vain attempt to answer Cixous, to “write your self. Your body must be heard” (880), it should be that freedom and theory, boundary-lessness, is where I reside. If anything should come from this, it is the knowing that theory is the most creative pursuit, and that creativity will always speak to theory. There are fewer divisions than any of us realise, and the leakiness of bodies, of this body, will get me there. The smell of this page is of lichor; a clean but heady smell, thick with old cells and a foetus’s breath. The smell of this page is of blood and saliva and milk mixed (the colour like rotten strawberries or the soaked pad at the bottom of your tray of supermarket mince). It is a smell that you will secretly savour, breathe deeply, and then long for lemon zest or the sharpness of coffee beans to send away that angelic fug. That milk and tears have a language of their own is undeniable. Kristeva says they are “metaphors of non-language, of a ‘semiotic’ that does not coincide with linguistic communication” (Stabat Mater 143) but what I know is that these fluids were the first language for my children. Were they the first language for me? Because “it must be true: babies drink language along with the breastmilk: Curling up over their tongues while they take siestas–Mots au lait, verbae cum lacta, palabros con leche” (Wasserman quoted in Giles 223). The enduring picture I have of myself as an infant is of a baby who didn’t cry, but my mother will tell you a different story, in the way that all of us do. She will tell you I didn’t smile until I was five months old (Soli and Jem were both beaming at three months). Born six weeks premature, my muscles took longer to find their place, to assemble themselves under my skin. She will tell you I screamed in the night, because all babies do. Is this non-language? Jem was unintelligible much of the time. I felt as if I was holding a puzzle. Three o’clock in the morning, having tried breastfeeds, a bath with Nick Drake’s Pink Moon, bouncing him in a baby sling on the fitball (wedged into a corner so that if I nodded off I would hopefully swoon backwards, and the wall would wake me), walking him around and around while rocking and singing, then breastfeeding again, and still he did not sleep, and still he cried and clawed at my cheeks and shoulders and wrists and writhed; I could not guess at what it was he needed. I had never been less concerned with the self that was me. I was all breasts and milk and a craving for barbecued chicken and watermelon at three in the morning because he was drinking every ounce of energy I had. I was arms and a voice. I was food. And then I learnt other things; about let downs and waking up in pools of the stuff. Wet. Everywhere. “Lactating bodies tend towards anarchy” (Bartlett 163). Any body will tend towards anarchy – there is so much to keep in – but there are only so many openings a person can keep track of, and breastfeeding meant a kind of levelling up, meant I was as far from clean and proper as I possibly could be (Kristeva, Powers of Horror 72).In the nights I was not alone. Caren could not breastfeed him, but could do everything else, and never said I have to work tomorrow, because she knew I was working too. During waking hours I watched him constantly for those mystical tired signs, which often were hungry signs, which quickly became overtired signs. There was no figuring it out. But Soli, with Soli, I knew. The language of babies had been sung into my bones. There is a grammar in crying, a calling out and telling, a way of knowing that is older than I’ll ever be. Those tiny bodies are brimming with semiotics. Knees pulled up is belly ache, arching is tired, a look to the side I-want-that-take-me-there-not-there. There. Curling in, the whole of him, is don’t-look-at-me-now-hands-away. Now he is one he uses his hands to tell me what he wants. Sign language because I sign and so, then, does he, but also an emphatic placing of my hands on his body or toys, utensils, swings, things. In the early hours of a Wednesday morning I tried to stroke his head, to close his wide-open eyes with my fingertips. He grabbed my hand and moved it to his chest before I could alight on the bridge of his nose. And yesterday he raised his arm into the air, then got my hand and placed it into his raised hand, then stood, and led me down to the laundry to play with the dustpan and broom. His body, literally, speaks.This is the language of mothers and babies. It is laid down in the darkest part of the night. Laid down like memory, like dreams, stitched into tiredness and circled with dread adrenalin and fear. It will never stop. That baby will cry and I will stare owl-eyed into the dark and bend my cracking knees (don’t shake the baby it will only make it worse don’t shake don’t). These babies will grow into children and then adults who will never remember those screaming nights, cots like cages, a stuffed toy pushed on them as if it could replace the warmth of skin and breath (please, please, little bear, replace the warmth of skin and breath). I will never remember it, but she will. They will never remember it, but we will. Kristeva says too that mothers are in a “catastrophe of identity which plunges the proper Name into that ‘unnameable’ that somehow involves our imaginary representations of femininity, non-language, or the body” (Stabat Mater 134). A catastrophe of identity. The me and the not-me. In the night, with a wrapped baby and aching biceps, the I-was batting quietly at the I-am. The I-am is all body. Arms to hold and bathe and change him, milk to feed him, a voice to sing and soothe him. The I-was is a different beast, made of words and books, uninterrupted conversation and the kind of self-obsession and autonomy I didn’t know existed until it was gone. Old friends stopped asking me about my day. They asked Caren, who had been at work, but not me. It did not matter that she was a woman; in this, for most people we spoke to, she was the public and I was the private, her work mattered and mine did not. Later she would commiserate and I would fume, but while it was happening, it was near impossible to contest. A catastrophe of identity. In a day I had fed and walked and cried and sung and fed and rocked and pointed and read books with no words and rolled inane balls across the lounge room floor and washed and sung and fed. I had circled in and around while the sun traced its arc. I had waited with impatience for adult company. I had loved harder than I ever had before. I had metamorphosed and nobody noticed. Nobody noticed. A catastrophe of identity it was, but the noise and visibility that the word catastrophe invokes was entirely absent. And where was the language to describe this peeling inside out? I was burnished bright by those sleepless nights, by the requirement of the I-am. And in those nights I learned what my mother already knew. That having children is a form of grief. That we lose. But that we gain. At 23, what’s lost is possibility. She must have seen her writer’s life drilling down to nothing. She knew that Sylvia Plath had placed her head, so carefully on its pillow, in that gas filled place. No pungent metaphor, just a poet, a mother, who could not continue. I had my babies at 34 and 36. I knew some of what I would lose, but had more than I needed. My mother had started out with not enough, and so was left concave and edged with desperation as she made her way through inner-city Sydney’s grime, her children singing from behind her wait for me, wait for me, Mama please wait for me, I’m going just as fast as I can.Nothing could be more ‘normal’ than that a maternal image should establish itself on the site of that tempered anguish known as love. No one is spared. Except perhaps the saint or the mystic, or the writer who, by force of language, can still manage nothing more than to demolish the fiction of the mother-as-love’s-mainstay and to identify with love as it really is: a fire of tongues, an escape from representation (Kristeva, Stabat Mater 145).We transformed, she and I. She hoped to make herself new with children. A writer born of writers, the growing and birthing of our tiny bodies forced her to place pen to paper, to fight to write. She carved a place for herself with words but it kept collapsing in on her. My father’s bi-polar rages, his scrubbing evil spirits from the soles of her shoes in the middle of the night, wore her down, and soon she inhabited that maternal image anyway, in spite of all her attempts to side step it. The mad mother, the single mother, the sad mother. And yes I remember those mothers. But I also remember her holding me so hard sometimes I couldn’t breathe properly, and that some nights when I couldn’t sleep she had warm eyes and made chamomile tea, and that she called me angel. A fire of tongues, but even she, with her words, couldn’t escape from representation. I am a writer born of writers born of writers (triply blessed or cursed with text). In my scramble to not be mad or bad or sad, I still could not escape the maternal image. More days than I can count I lay under my babies wishing I could be somewhere, anywhere else, but they needed to sleep or feed or be. With me. Held captive by the need to be a good mother, to be the best mother, no saint or mystic presenting itself, all I could do was write. Whole poems sprang unbidden and complete from my pen. My love for my children, that fire of tongues, was demolishing me, and the only way through was to inhabit this vessel of text, to imbibe the language of bodies and tears and night, and make from it my boat.Those children wrote my body in the night. They taught me about desire, that unbounded scribbling thing that will not be bound by subjectivity, by me. They taught me that “the body is literally written on, inscribed, by desire and signification” (Grosz 60), and every morning I woke with ashen bones and poetry aching out through my pores, with my body writing me.This Mother ThingI maintain that I do not have to leavethe house at nightall leathery and eyelinered,all booted up and raw.I maintain that I do not miss thosesmoky rooms (wait that’s not allowed any more)where we strut and, without looking,compare tattoos.Because two years ago I had you.You with your blonde hair shining, your eyes like a creek after rain, that veinthat’s so blue on the side of your small nosethat people think you’ve been bruised.Because two years ago you cameout of me and landed here and grew. There is no going out. We (she and me) washand cook and wash and clean and love.This mother thing is the making of me but I missthose pulsing rooms,the feel of all of you pressing in onall of me.This mother thing is the making of me. And in text, in poetry, I find my home. “You only have to look at the Medusa straight on to see her. And she’s not deadly. She’s beautiful and she’s laughing” (Cixous 885). The mother-body writes herself, and is made new. The mother-body writes her own mother, and knows she was always-already here. The mother-body births, and breastfeeds, and turns to me in the aching night and says this: the Medusa? The Medusa is me.ReferencesBartlett, Alison. Breastwork: Rethinking Breastfeeding. Sydney: UNSW Press, 2005.Cixous, Hélène, Keith Cohen, and Paula Cohen (Trans.). "The Laugh of the Medusa." Signs 1.4 (1976): 875-93. Giles, Fiona. Fresh Milk. Crows Nest, NSW: Allen & Unwin, 2003. Grosz, Elizabeth. Volatile Bodies: Toward a Corporeal Feminism. St Leonards, NSW: Allen & Unwin, 1994.Kristeva, Julia, and Leon S. Roudiez (Trans.) Powers of Horror: An Essay on Abjection. New York: Columbia University Press, 1982.Kristeva, Julia, and Arthur Goldhammer (Trans.). "Stabat Mater." Poetics Today 6.1-2 (1985): 133-52.

In this thesis, experiments and simulations are performed to study the deployment dynamics of space webs and space booms, focusing on the deployment and stabilization phases of the space web and the behavior of the bi-stable tape spring booms after long-term stowage. The space web, Suaineadh, was launched onboard the sounding rocket REXUS-12 from the Swedish launch base Esrange in Kiruna on 19 March 2012. It served as a technology demonstrator for a space web. A reaction wheel was used to actively control the deployment and stabilization states of the 2×2 m2 space web. After ejection from the rocket, the web was deployed but entanglements occurred since the web did not start to deploy at the specified angular velocity. The deployment dynamics was reconstructed by simulations from the information recorded by inertial measurement units and cameras. Simulations show that if the web would have started to deploy at the specified angular velocity, the web would most likely have been deployed and stabilized in space by the motor, reaction wheel and controller used in the experiment. A modified control method was developed to stabilize the out-of-plane motions before or during deployment. New web arms with tape springs were proposed to avoid entanglements. A deployable booms assembly composed of four 1-m long bi-stable glass fiber tape springs was designed for the electromagnetically clean 3U CubeSat Small Explorer for Advanced Missions (SEAM). The deployment dynamics and reliability of the SEAM boom design after long-term stowage were tested by on-ground experiments. A simple analytical model was developed to predict the deployment dynamics and to assess the effects of the GOLS and the combined effects of friction, viscoelastic strain energy relaxation, and other factors that act to decrease the deployment force. In order to mitigate the viscoelastic effects and thus ensure self-deployment, different tape springs were designed, manufactured and tested. A numerical model was used to assess the long-term stowage effects on the deployment capability of bi-stable tape springs including the friction, nonlinear-elastic and viscoelastic effects. A finite element method was used to model a meter-class fully coiled bi-stable tape spring boom and verified by analytical models.

QC 20170508

SEAM

The recent development of CubeSat nano-satellites shows that it is an effective way to send a payload onto orbit, as it is a relatively inexpensive and quick access to space. If the small size of these satellites is their main advantage, it is also the principal source of problems when it comes to designing it. The control electronics, electric power system and the payload are limited in mass and have to t in a tiny ten-centimeter cube. The necessity of a compact deployable structure to hold the payload once the satellite reached its orbit is one of the principal subject of study for the design of a CubeSat. In the CubeSat program SWIM (Space Weather using Ion Spectrometers and Magnetometers) that KTH takes part in, the  deployablestructure developed consists of bi-stable semi-tubular booms made by a woven-composite fabric. Preliminary tests show that this structure is very compact and stable in the packaged con guration while being suciently long and stiin the deployed con guration. However little is known about the deployment phase, the physical model of the booms is very inaccurate in determining the deployment force and speed, because of the complexity of the material mechanics behind it. Modeling a woven composite material in a nite element analysis software is a dicult task due the structure of the material itself. The ber yarns interlace each other like in textile material, and they are impregnated in a soft matrix resin. Although in-plane properties of these materials can be calculated accurately using the classic lamination theory (CLT), the corresponding out-of-plane properties lack any accuracy for one-ply woven composites. Solutions are found through micromechanical approaches but these models are dicult to implement and are computationally expensive. The solution to this problem is to decline the CLT model of the material in two versions, each with a its own purpose. This paper presents rst a CLT model of the woven composite which aim is to predict in-plane properties accurately and giving a good estimation of the out-of-plane properties. The second version of the CLT model is developed with the aim of predicting accurately the amount of strain energy stored and the stable radius of the rolled-up con guration. The purpose of this version is to be used in deployment analysis. This paper also presents the main lines of a fully parameterized nite element model of the deployment analysis for future use.

The paper introduces tape springs as elements of fully compliant mechanisms. The localized folds of tape springs serve as compact revolute joints, with a very small radius and large range of motion, and the unfolded straight segments serve as links. By exploiting a tape spring’s ability to function as both links and joints, we present a new method of realizing fully compliant mechanisms with further simplification in their construction. Tape springs, typically found in carpenter tape rules, are thin-walled strips having constant thickness, zero longitudinal curvature, and a constant transverse curvature. The paper presents a closed-loop tape spring mechanism. By representing its folds as idealized revolute joints and its variable length links as sliding joints connecting rigid links, we present a modified Gruebler’s equation to determine its kinematic and idle degrees of freedom. To realize practical utility of tape spring mechanisms, we propose a simple actuation scheme incorporating shape memory alloy (SMA) wire actuators and successfully demonstrate its performance with a proof-of-concept prototype. The paper also presents potential applications for actuated tape spring mechanisms including a large displacement translational mechanism, planar positioning mechanisms, bi-stable, multi-stable, and variable stiffness mechanisms.

Currently, the small satellite mechanisms that are used to deploy sensors and antennae in space have been restricted to simple one arm pin jointed members or telescopic mechanisms. This means, to deploy multiple sensors, multiple actuators and controllers are required. However, simple rigid link mechanisms, like the 6-bar hexagonal mechanism described in this paper, give the freedom to incorporate a greater number of sensor platforms in one deployable structure and also helps reduce the number of actuators. In fact, by the use of boom technology, the entire mechanism can be deployed by a single tape-spring boom. Further, to make these structures more robust and stiffer at the joints, rotational springs can be used. In this paper, an attempt is made to study the stiffness and stability of such mechanisms at their equilibrium points. Also since the positions and orientations of the sensor platforms are critical, it is shown through a few examples how these parameters can be adjusted just by tweaking the preloads of the rotational springs. The tape-spring boom — which is bi-stable in nature — offers further stiffness to the structure in its deployed state. It is well known now and also well established by the theory of mechanics of materials that by arranging multiple tape springs in certain orientations within the boom; a boom can be obtained with significant axial and flexural stiffness in its deployed state. Through modal analyses at equilibrium and by looking at the characteristics of the Hessian of the potential energy function, it is also shown how this significantly rigid boom affects the stiffness and stability of the structure. Herein, the force method of matrix analysis for deployable structures is used for analyses. This paper also discusses the possibilities of the system failing due to insufficient actuation force by the boom — the condition where the boom does not reach its second stable position.