Analysis and optimization for a hexapod walking robot for planetary missions

La tecnología de las máquinas móviles autónomas ha sido objeto de una gran investigación y desarrollo en las últimas décadas. En muchas actividades y entornos, los robots pueden realizar operaciones que son duras, peligrosas o simplemente imposibles para los humanos. La exploración planetaria es un buen ejemplo de un entorno donde los robots son necesarios para realizar las tareas requeridas por los científicos. La reciente exploración de Marte con robots autónomos nos ha mostrado la capacidad de las nuevas tecnologías. Desde la invención de la rueda, que esta acertadamente considerado como el mayor invento en la historia del transporte humano, casi todos los vehículos para exploración planetaria han empleado las ruedas para su desplazamiento. Las nuevas misiones planetarias demandan maquinas cada vez mas complejas. En esta Tesis se propone un nuevo diseño de un robot con patas o maquina andante que ofrecerá claras ventajas en entornos extremos. Se demostrara que puede desplazarse en los terrenos donde los robots con ruedas son ineficientes, convirtiéndolo en una elección perfecta para misiones planetarias. Se presenta una reseña histórica de los principales misiones espaciales, en particular aquellos dirigidos a la exploración planetaria. A través de este estudio será posible analizar las desventajas de los robots con ruedas utilizados en misiones anteriores. El diseño propuesto de robot con patas será presentado como una alternativa para aquellas misiones donde los robots con ruedas puedan no ser la mejor opción. En esta tesis se presenta el diseño mecánico de un robot de seis patas capaz de soportar las grandes fuerzas y momentos derivadas del movimiento de avance. Una vez concluido el diseño mecánico es necesario realizar un análisis que permita entender el movimiento y comportamiento de una maquina de esta complejidad. Las ecuaciones de movimiento del robot serán validadas por dos métodos: cinemático y dinámico. Dos códigos Matlab® han sido desarrollados para resolver dichos sistemas de ecuaciones y han sido verificados por un tercer método, un modelo de elementos finitos, que también verifica el diseño mecánico. El robot con patas presentado, ha sido diseñado para la exploración planetaria en Marte. El comportamiento del robot durante sus desplazamientos será probado mediante un código de Matlab®, desarrollado para esta tesis, que permite modificar las trayectorias, el tipo de terreno, y el número y altura de los obstáculos. Estos terrenos y requisitos iniciales no han sido elegidos de forma aleatoria, si no que están basados en mi experiencia como miembro del equipo de MSL-NASA que opera un instrumento a bordo del rover Curiosity en Marte. El robot con patas desarrollado y fabricado por el Centro de Astrobiología (INTA-CSIC), esta basado en el diseño mecánico y análisis presentados en esta tesis. ABSTRACT The autonomous machines technology has undergone a major research and development during the last decades. In many activities and environments, robots can perform operations that are tought, dangerous or simply imposible to humans. Planetary exploration is a good example of such environment where robots are needed to perform the tasks required by the scientits. Recent Mars exploration based on autonomous vehicles has shown us the capacity of the new technologies. From the invention of the wheel, which is rightly regarded as the greatest invention in the history of human transportation, nearly all-planetary vehicles are based in wheeled locomotion, but new missions demand new types of machines due to the complex tasks needed to be performed. It will be proposed in this thesis a new design of a legged robot or walking machine, which may offer clear advantages in tough environments. This Thesis will show that the proposed walking machine can travel, were terrain difficulties make wheeled vehicles ineffective, making it a perfect choice for planetary mission. A historical background of the main space missions, in particular those aimed at planetary exploration will be presented. From this study the disadvantages found in the existing wheel rovers will be analysed. The legged robot designed will be introduced as an alternative were wheeled rovers could be no longer the best option for planetary exploration. This thesis introduces the mechanical design of a six-leg robot capable of withstanding high forces and moments due to the walking motion. Once the mechanical design is concluded, and in order to analyse a machine of this complexity an understanding of its movement and behaviour is mandatory. This movement equation will be validated by two methods: kinematics and dynamics. Two Matlab® codes have been developed to solve the systems of equations and validated by a third method, a finite element model, which also verifies the mechanical design. The legged robot presented has been designed for a Mars planetary exploration. The movement behaviour of the robot will be tested in a Matlab® code developed that allows to modify the trajectories, the type of terrain, number and height of obstacles. These terrains and initial requirements have not been chosen randomly, those are based on my experience as a member of the MSL NASA team, which operates an instrument on-board of the Curiosity rover in Mars. The walking robot developed and manufactured by the Center of Astrobiology (CAB) is based in the mechanical design and analysis that will be presented in this thesis.

An Adjustable Compliant Joint for Lower-Limb Exoskeletons

The field of exoskeletons and wearable devices for walking assistance and rehabilitation has advanced considerably over the past few years. Currently, commercial devices contain joints with stiff actuators that cannot adapt to unpredictable environments. These actuators consume more energy and may not be appropriate for human-machine interactions. Thus, adjustable compliant actuators are being cautiously incorporated into new exoskeletons and active orthoses. Some simulation-based studies have evaluated the benefits of incorporating compliant joints into such devices. Another reason that compliant actuators are desirable is that spasticity and spasmodic movements are common among patients with motor deficiencies; compliant actuators could efficiently absorb these perturbations and improve joint control. In this paper, we provide an overview of the requirements that must be fulfilled by these actuators while evaluating the behavior of leg joints in the locomotion cycle. A brief review of existing compliant actuators is conducted, and our proposed variable stiffness actuator prototype is presented and evaluated. The actuator prototype is implemented in an exoskeleton knee joint operated by a state machine that exploits the dynamics of the leg, resulting in a reduction in actuation energy demand and better adaptability to disturbances.

Dopamine-dependent responses to morphine depend on glucocorticoid receptors

Previous work has shown that glucocorticoid hormones facilitate the behavioral and dopaminergic effects of morphine. In this study we examined the possible role in these effects of the two central corticosteroid receptor types: mineralocorticoid receptor (MR), and glucocorticoid receptor (GR). To accomplish this, specific antagonists of these receptors were infused intracerebroventricularly and 2 hr later we measured: (i) locomotor activity induced by a systemic injection of morphine (2 mg/kg); (ii) locomotor activity induced by an infusion of morphine (1 μg per side) into the ventral tegmental area, which is a dopamine-dependent behavioral response to morphine; (iii) morphine-induced dopamine release in the nucleus accumbens, a dopaminergic projection site mediating the locomotor and reinforcing effects of drugs of abuse. Blockade of MRs by spironolactone had no significant effects on locomotion induced by systemic morphine. In contrast, blockade of GRs by either RU38486 or RU39305, which is devoid of antiprogesterone effects, reduced the locomotor response to morphine, and this effect was dose dependent. GR antagonists also reduced the locomotor response to intraventral tegmental area morphine as well as the basal and morphine-induced increase in accumbens dopamine, as measured by microdialysis in freely moving rats. In contrast, spironolactone did not modify dopamine release. In conclusion, glucocorticoids, via GRs, facilitate the dopamine-dependent behavioral effects of morphine, probably by facilitating dopamine release. The possibility of decreasing the behavioral and dopaminergic effects of opioids by an acute administration of GR antagonists may open new therapeutic strategies for treatment of drug addiction.

Dictyostelium myosin II null mutant can still cap Con A receptors

Cross-linked antigens on the surface of a motile cell cap at the trailing end of the cell. In Dictyostelium discoideum, myosin II null mutants have previously been reported to be unable to cap Con A receptors, although they are able to locomote. This finding implicated myosin II as an essential component of the capping mechanism, although not of the machinery for locomotion. Here we show that myosin II null mutants do cap Con A receptors, albeit less efficiently than does wild type. This shows that cap formation is not absolutely dependent on myosin II and that a close mechanistic relationship between capping, particle movement, and cell migration may still exist.

Response-reinforcement learning is dependent on N-methyl-d-aspartate receptor activation in the nucleus accumbens core

The nucleus accumbens, a site within the ventral striatum, is best known for its prominent role in mediating the reinforcing effects of drugs of abuse such as cocaine, alcohol, and nicotine. Indeed, it is generally believed that this structure subserves motivated behaviors, such as feeding, drinking, sexual behavior, and exploratory locomotion, which are elicited by natural rewards or incentive stimuli. A basic rule of positive reinforcement is that motor responses will increase in magnitude and vigor if followed by a rewarding event. It is likely, therefore, that the nucleus accumbens may serve as a substrate for reinforcement learning. However, there is surprisingly little information concerning the neural mechanisms by which appetitive responses are learned. In the present study, we report that treatment of the nucleus accumbens core with the selective competitive N-methyl-d-aspartate (NMDA) antagonist 2-amino-5-phosphonopentanoic acid (AP-5; 5 nmol/0.5 μl bilaterally) impairs response-reinforcement learning in the acquisition of a simple lever-press task to obtain food. Once the rats learned the task, AP-5 had no effect, demonstrating the requirement of NMDA receptor-dependent plasticity in the early stages of learning. Infusion of AP-5 into the accumbens shell produced a much smaller impairment of learning. Additional experiments showed that AP-5 core-treated rats had normal feeding and locomotor responses and were capable of acquiring stimulus-reward associations. We hypothesize that stimulation of NMDA receptors within the accumbens core is a key process through which motor responses become established in response to reinforcing stimuli. Further, this mechanism, may also play a critical role in the motivational and addictive properties of drugs of abuse.

Altered emotional and locomotor responses in mice deficient in the transcription factor CREM

Various transcription factors act as nuclear effectors of the cAMP-dependent signaling pathway. These are the products of three genes in the mouse, CREB, CRE modulator (CREM), and ATF-1. CREM proteins are thought to play important roles within the hypothalamic–pituitary axis and in the control of rhythmic functions in the pineal gland. We have generated CREM-mutant mice and investigated their response in a variety of behavioral tests. CREM-null mice show a drastic increase in locomotion. In contrast to normal mice, the CREM-deficient mice show equal locomotor activity during the circadian cycle. The anatomy of the hypothalamic suprachiasmatic nuclei, the center of the endogenous pacemaker, is normal in mutant mice. Remarkably, CREM mutant mice also elicit a different emotional state, revealed by a lower anxiety in two different behavioral models, but they preserve the conditioned reactiveness to stress. These results demonstrate the high degree of functional specificity of each cAMP-responsive transcription factor in behavioral control.

The origin and evolution of animal appendages

Animals have evolved diverse appendages adapted for locomotion, feeding and other functions. The genetics underlying appendage formation are best understood in insects and vertebrates. The expression of the Distal-less (Dll) homeoprotein during arthropod limb outgrowth and of Dll orthologs (Dlx) in fish fin and tetrapod limb buds led us to examine whether expression of this regulatory gene may be a general feature of appendage formation in protostomes and deuterostomes. We find that Dll is expressed along the proximodistal axis of developing polychaete annelid parapodia, onychophoran lobopodia, ascidian ampullae, and even echinoderm tube feet. Dll/Dlx expression in such diverse appendages in these six coelomate phyla could be convergent, but this would have required the independent co-option of Dll/Dlx several times in evolution. It appears more likely that ectodermal Dll/Dlx expression along proximodistal axes originated once in a common ancestor and has been used subsequently to pattern body wall outgrowths in a variety of organisms. We suggest that this pre-Cambrian ancestor of most protostomes and the deuterostomes possessed elements of the genetic machinery for and may have even borne appendages.

α1 and α2 Integrins Mediate Invasive Activity of Mouse Mammary Carcinoma Cells through Regulation of Stromelysin-1 Expression

Tumor cell invasion relies on cell migration and extracellular matrix proteolysis. We investigated the contribution of different integrins to the invasive activity of mouse mammary carcinoma cells. Antibodies against integrin subunits α6 and β1, but not against α1 and α2, inhibited cell locomotion on a reconstituted basement membrane in two-dimensional cell migration assays, whereas antibodies against β1, but not against α6 or α2, interfered with cell adhesion to basement membrane constituents. Blocking antibodies against α1 integrins impaired only cell adhesion to type IV collagen. Antibodies against α1, α2, α6, and β1, but not α5, integrin subunits reduced invasion of a reconstituted basement membrane. Integrins α1 and α2, which contributed only marginally to motility and adhesion, regulated proteinase production. Antibodies against α1 and α2, but not α6 and β1, integrin subunits inhibited both transcription and protein expression of the matrix metalloproteinase stromelysin-1. Inhibition of tumor cell invasion by antibodies against α1 and α2 was reversed by addition of recombinant stromelysin-1. In contrast, stromelysin-1 could not rescue invasion inhibited by anti-α6 antibodies. Our data indicate that α1 and α2 integrins confer invasive behavior by regulating stromelysin-1 expression, whereas α6 integrins regulate cell motility. These results provide new insights into the specific functions of integrins during tumor cell invasion.

High Resolution Detection of Mechanical Forces Exerted by Locomoting Fibroblasts on the Substrate

We have developed a new approach to detect mechanical forces exerted by locomoting fibroblasts on the substrate. Cells were cultured on elastic, collagen-coated polyacrylamide sheets embedded with 0.2-μm fluorescent beads. Forces exerted by the cell cause deformation of the substrate and displacement of the beads. By recording the position of beads during cell locomotion and after cell removal, we discovered that most forces were radially distributed, switching direction in the anterior region. Deformations near the leading edge were strong, transient, and variable in magnitude, consistent with active local contractions, whereas those in the posterior region were weaker, more stable, and more uniform, consistent with passive resistance. Treatment of cells with cytochalasin D or myosin II inhibitors caused relaxation of the forces, suggesting that they are generated primarily via actin–myosin II interactions; treatment with nocodazole caused no immediate effect on forces. Immunofluorescence indicated that the frontal region of strong deformation contained many vinculin plaques but no apparent concentration of actin or myosin II filaments. Strong mechanical forces in the anterior region, generated by locally activated myosin II and transmitted through vinculin-rich structures, likely play a major role in cell locomotion and in mechanical signaling with the surrounding environment.

Circadian modulation of dopamine receptor responsiveness in Drosophila melanogaster

We investigated the circadian function of Drosophila dopamine receptors by using a behaviorally active decapitated preparation that allows for direct application of drugs to the nerve cord. Quinpirole, a D2-like dopamine receptor agonist, induces reflexive locomotion in decapitated flies. We show that the amount of locomotion induced changes as a function of the time of day, with the highest responsiveness to quinpirole during the subjective night. Furthermore, dopamine receptor responsiveness is under circadian control and depends on the normal function of the period gene. The head pacemaker is at least partly dispensable for the circadian modulation of quinpirole-induced locomotion, because changes in agonist responsiveness persist in decapitated flies that are aged for 12 h. This finding suggests a role for the period-dependent molecular oscillators in the body in the modulation of amine receptor responsiveness.

Molecular phylogenetic analysis of evolutionary trends in stonefly wing structure and locomotor behavior

Insects in the order Plecoptera (stoneflies) use a form of two-dimensional aerodynamic locomotion called surface skimming to move across water surfaces. Because their weight is supported by water, skimmers can achieve effective aerodynamic locomotion even with small wings and weak flight muscles. These mechanical features stimulated the hypothesis that surface skimming may have been an intermediate stage in the evolution of insect flight, which has perhaps been retained in certain modern stoneflies. Here we present a phylogeny of Plecoptera based on nucleotide sequence data from the small subunit rRNA (18S) gene. By mapping locomotor behavior and wing structural data onto the phylogeny, we distinguish between the competing hypotheses that skimming is a retained ancestral trait or, alternatively, a relatively recent loss of flight. Our results show that basal stoneflies are surface skimmers, and that various forms of surface skimming are distributed widely across the plecopteran phylogeny. Stonefly wings show evolutionary trends in the number of cross veins and the thickness of the cuticle of the longitudinal veins that are consistent with elaboration and diversification of flight-related traits. These data support the hypothesis that the first stoneflies were surface skimmers, and that wing structures important for aerial flight have become elaborated and more diverse during the radiation of modern stoneflies.

How well can an amoeba climb?

We report here our efforts to measure the crawling force generated by cells undergoing amoeboid locomotion. In a centrifuge microscope, acceleration was increased until amoebae of Dictyostelium discoideum were “stalled” or no longer able to “climb up.” The “apparent weight” of the amoebae at stalling rpm in myosin mutants depended on the presence of myosin II (but not myosins IA and IB) and paralleled the cortical strength of the cells. Surprisingly, however, the cell stalled not only in low-density media as expected but also in media with densities greater than the cell density where the buoyant force should push the amoeba upward. We find that the leading pseudopod is bent under centrifugal force in all stalled amoebae, suggesting that this pseudopod is very dense indeed. This finding also suggests that directional cell locomotion against resistive forces requires a turgid forward-pointing pseudopod, most likely sustained by cortical actomyosin II.

Pharmacological and immunohistochemical evidence for a functional nitric oxide synthase system in rat peritoneal eosinophils

Eosinophil migration in vivo is markedly attenuated in rats treated chronically with the NO synthase (NOS) inhibitor Nω-nitro-l-arginine methyl ester (l-NAME). In this study, we investigated the existence of a NOS system in eosinophils. Our results demonstrated that rat peritoneal eosinophils strongly express both type II (30.2 ± 11.6% of counted cells) and type III (24.7 ± 7.4% of counted cells) NOS, as detected by immunohistochemistry using affinity purified mouse mAbs. Eosinophil migration in vitro was evaluated by using 48-well microchemotaxis chambers and the chemotactic agents used were N-formyl-methionyl-leucyl-phenylalanine (fMLP, 5 × 10−8 M) and leukotriene B4 (LTB4, 10−8 M). l-NAME (but not d-NAME) significantly inhibited the eosinophil migration induced by both fMLP (54% reduction for 1.0 mM; P < 0.05) and LTB4 (61% reduction for 1.0 mM; P < 0.05). In addition, the type II NOS inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine and the type I/II NOS inhibitor 1-(2-trifluoromethylphenyl) imidazole also markedly (P < 0.05) attenuated fMLP- (52% and 38% reduction for 1.0 mM, respectively) and LTB4- (52% and 51% reduction for 1.0 mM, respectively) induced migration. The inhibition of eosinophil migration by l-NAME was mimicked by the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a] quinoxalin-1-one (0.01 and 0.1 mM) and reversed by either sodium nitroprusside (0.1 mM) or dibutyryl cyclic GMP (1 mM). We conclude that eosinophils do express NO synthase(s) and that nitric oxide plays an essential role in eosinophil locomotion by acting through a cyclic GMP transduction mechanism.

The role of the D2 dopamine receptor (D2R) in A2A adenosine receptor (A2AR)-mediated behavioral and cellular responses as revealed by A2A and D2 receptor knockout mice

The A2AR is largely coexpressed with D2Rs and enkephalin mRNA in the striatum where it modulates dopaminergic activity. Activation of the A2AR antagonizes D2R-mediated behavioral and neurochemical effects in the basal ganglia through a mechanism that may involve direct A2AR–D2R interaction. However, whether the D2R is required for the A2AR to exert its neural function is an open question. In this study, we examined the role of D2Rs in A2AR-induced behavioral and cellular responses, by using genetic knockout (KO) models (mice deficient in A2ARs or D2Rs or both). Behavioral analysis shows that the A2AR agonist 2–4-(2-carboxyethyl)phenethylamino-5′-N-ethylcarboxamidoadenosine reduced spontaneous as well as amphetamine-induced locomotion in both D2 KO and wild-type mice. Conversely, the nonselective adenosine antagonist caffeine and the A2AR antagonist 8-(3-chlorostyryl)caffeine produced motor stimulation in mice lacking the D2R, although the stimulation was significantly attentuated. At the cellular level, A2AR inactivation counteracted the increase in enkephalin expression in striatopallidal neurons caused by D2R deficiency. Consistent with the D2 KO phenotype, A2AR inactivation partially reversed both acute D2R antagonist (haloperidol)-induced catalepsy and chronic haloperidol-induced enkephalin mRNA expression. Together, these results demonstrate that A2ARs elicit behavioral and cellular responses despite either the genetic deficiency or pharmacological blockade of D2Rs. Thus, A2AR-mediated neural functions are partially independent of D2Rs. Moreover, endogenous adenosine acting at striatal A2ARs may be most accurately viewed as a facilitative modulator of striatal neuronal activity rather than simply as an inhibitory modulator of D2R neurotransmission.

Characterization of a high-voltage-activated IA current with a role in spike timing and locomotor pattern generation

Transient A-type K+ channels (IA) in neurons have been implicated in the delay of the spike onset and the decrease in the firing frequency. Here we have characterized biophysically and pharmacologically an IA current in lamprey locomotor network neurons that is activated by suprathreshold depolarization and is specifically blocked by catechol at 100 μM. The biophysical properties of this current are similar to the mammalian Kv3.4 channel. The role of the IA current both in single neuron firing and in locomotor pattern generation was analyzed. The IA current facilitates Na+ channel recovery from inactivation and thus sustains repetitive firing. The role of the IA current in motor pattern generation was examined by applying catechol during fictive locomotion induced by N-methyl-d-aspartate. Blockade of this current increased the locomotor burst frequency and decreased the firing of motoneurons. Although an alternating motor pattern could still be generated, the cycle duration was less regular, with ventral roots bursts failing on some cycles. Our results thus provide insights into the contribution of a high-voltage-activated IA current to the regulation of firing properties and motor coordination in the lamprey spinal cord.