Winching up heavy loads with a compliant arm: a new local joint controller

G protein-coupled receptors (GPCRs) play a pivotal role in regulating key physiological events in all animal species. Recent advances in collective analysis of genes and proteins revealed numerous potential neuropeptides and GPCRs from insect species, allowing for the characterization of peptide–receptor pairs. In this work, we used fluorescence resonance energy transfer (FRET)-based genetically encoded biosensors in intact mammalian cells to study the pharmacological features of the cognate GPCR of the type-C allatostatin (AST-C) peptide from the stick insect, Carausius morosus. Analysis of multiple downstream pathways revealed that AST-C can activate the human Gi2 protein, and not Gs or Gq, through AST-C receptor (AlstRC). Activated AlstRC recruits β-arrestin2 independent of the Gi protein but stimulates ERK phosphorylation in a Gi protein-dependent manner. Identification of Gαi-, arrestin-, and GRK-like transcripts from C. morosus revealed high evolutionary conservation at the G protein level, while β-arrestins and GRKs displayed less conservation. In conclusion, our study provides experimental and homology-based evidence on the functionality of vertebrate G proteins and downstream signaling biosensors to characterize early signaling steps of an insect GPCR. These results may serve as a scaffold for developing assays to characterize pharmacological and structural aspects of other insect GPCRs and can be used in deorphanization and pesticide studies.

In silico characterization of adipokinetic hormone receptor and screening for pesticide candidates against stick insect, Carausius morosus

Traditional droop control in AC microgrids relies on telecommunication between a central controller and distributed generators for frequency and voltage restoration. This makes optimal operation of the microgrid vulnerable to a single point of failure i.e. the central controller. Recently, a decentralised control strategy for parallel inverters has been proposed that supplies an AC microgrid load with its demanded current in agreed and equitable fashion, based on local information only and using no telecommunications. In this control strategy the locally measured downstream current is used to derive the current reference for the primary-level control loop in each distributed generator. This facilitates stable operation of the microgrid, with an agreed share of the load current contributed by each inverter. The agreed current sharing distribution is assumed as apriori knowledge, amounting to the assumption that each inverter knows its relative position among the chain of inverters and that all inverters are fully operational. However, in practice, inverter current sharing must be dynamically modified to deal with the loss (or addition) of inverters, and relative changes in their power capabilities. To address this issue, this paper proposes use of a special type of modulator with explicit spectra shaping ability. In the low harmonic pollution environment, which the modulator ensures, it is shown that harmonic power line communication can be utilised for dynamically adjusting the agreed load sharing characteristic.

Traditional droop control in AC microgrids relies on telecommunication between a central controller and distributed generators for frequency and voltage restoration. This makes optimal operation of the microgrid vulnerable to a single point of failure i.e. the central controller. The aim of this paper is to propose a decentralised control strategy that supplies the microgrid load with its demanded current in agreed and equitable fashion, based on local information only and using no telecommunications. Fundamental to the proposed concept is a parallel arrangement between distributed generators and the local loads. In this arrangement the locally measured downstream current is used to derive the current reference for the primary-level control loop in each distributed generator. Use of the downstream current as an implicit communication method facilitates stable operation of the microgrid and elimination of undesired circulating currents. The paper validates the developed concept via detailed simulations under a range of realistic scenarios.

Tryptophan 2,3-dioxygenase was studied in the stick insect,Carausius morosus. During the 6th larvl instar, the activity of the enzyme rises from the 5th molt until the premolt stage and declines prior to the imaginal molt (Fig. 1). In adult stick insects, enzyme activity rises continuously to a level twice as high as in the 6th larval instar (Fig. 2). The molecular weight of tryptophan 2,3-dioxygenase was estimated at 120.000; the optimal pH of the reaction is about 7.5. Substrate concentration for half-maximal reaction rate, S(0.5) is 0.58·10−3 M; the binding curve is sigmoid with a Hill coefficient of 1.9 (Fig. 4). The reaction is preceded by a lag period of about 30 min.

Stick insects (Carausius morosus) develop pseudotumors in aging adults. Pseudotumor formation starts at the M2 midgut region where an accumulation of stomatogastric nerve terminals is observed. Pseudotumors arise from dying columnar cells whose basal parts form an "amorphous substance" at the basement membrane whereas the apical parts, including the nucleus, are expelled into the gut lumen. The "amorphous substance" is ensheathed by hemocytes. These nodules, which do not melanize, characterize the phenotype of the pseudotumors. With age, cell death and pseudotumor infestation increases. It is shown that the maintenance of midgut tissue homoeostasis is disturbed and becomes more serious with growing pseudotumor incidence. The increased death rate of differentiated columnar cells is no longer compensated by the proliferation of regenerative cells, i.e., intestinal stem cells, in the midgut nidi. The appearance of "holes" in the intestinal wall is evidently a causative factor of premature death. Extirpation of the hypocerebral ganglion in young adults of the stick insect (before the onset of spontaneous pseudotumor formation) provokes the apoptosis of a large number of columnar cells within 24 h and the formation of pseudotumors that are histologically identical with spontaneous ones. We conclude that the stomatogastric nervous system plays a decisive role in the regulatory mechanism maintaining midgut tissue homeostasis. The possibility of experimentally manipulating the regulatory system provides a valuable tool for the exploration of extrinsic factors involved into the feedback circuitry of tissue homeostasis. The fact that comparable pseudotumors were observed in a number of orthopteromorphan species, where they could also be induced by the interruption of the stomatogastric nervous system, indicates that its role in tissue homoeostasis may be widespread in insects and possibly represent a general principle.

Operations involving safe interactions in unstructured environments require robots with adapting behaviors. Compliant manipulators are a promising technology to achieve this goal. Despite that, some classical control problems such as following a trajectory are still open. A typical solution is to compensate the system dynamics with feedback loops. However, this solution increases the effective robot stiffness and jeopardizes the safety property provided by the compliant design. On the other hand, purely feedforward approaches can achieve good tracking performance while preserving the robot intrinsic compliance. However, a feedforward control framework for robots with passive elastic joints is still missing. This article presents an iterative learning control algorithm for purely feedforward trajectory tracking for compliant underactuated arms. Each arm is composed of active elastic joints and a generic number of passive ones connected through rigid links. We prove the convergence of the iterative method, also in the presence of uncertainties and bounded disturbances. Different output functions are analyzed providing conditions, based on the system inertial properties that ensure the algorithm applicability. Additionally, an automatic selection of the learning gain is proposed. Finally, we extensively validate the theoretical results with simulations and experiments.

Stick insects (Carausius morosus) walking on a wheel were perturbed by restricting the forward protraction of individual legs. A barrier placed before a single middle or rear leg prevented that leg from reaching its normal protraction endpoint but allowed it unimpeded retraction. Upon striking the barrier, the protracting leg attempted to get past it and thereby prolonged protraction. This prolongation increased with the extent to which the obstruction infringed upon the leg's normal step range. Barriers placed near the midpoint of this range elicited large perturbations: the blocked leg often continued its protraction throughout many step cycles of the other legs (Fig. 1 E, F). For the most part walking was irregular and smooth forward progression was disrupted. Nevertheless, the infrequent steps by the affected leg usually were coordinated with those of the adjacent ipsilateral legs. More rostral barrier positions elicited smaller perturbations: the blocked leg usually made one step in each step cycle of the other legs (Fig. 1 B, C, D, G). Measurements for these regular step sequences showed quantitatively that protraction duration increased in proportion to the severity of the infringement on normal leg movement (Figs. 3, 4). The fraction of the step period occupied by protraction increased from ca. 10% for normal walking to ca. 50% for caudal barrier positions. This proportionality is interpreted to show the importance of spatial components of the walking program. When one leg was obstructed, its extended protraction influenced the stepping of the three adjacent legs as follows. First, the ipsilateral rostral leg showed the largest change: its protraction onset was regularly delayed for the duration of the extended protraction (Figs. 4, 7, 8), demonstrating a strong, centrally mediated inhibition. The presence of a further delay of up to 100 to 140 ms suggests that peripheral input from the protracting leg may be important for releasing this inhibition. Second, steps by an adjacent caudal leg were not measurably affected. However, the method may not have sufficed to reveal such effects because during regular walking middle leg protractions rarely lasted long enough to conflict with subsequent steps by the ipsilateral rear leg. Third, contralateral effects differed between middle and rear leg obstructions. If the obstructed leg was a middle leg, its extended protraction had little effect upon stepping by the contralateral middle leg: the latter leg frequently protracted while the blocked leg continued its protraction and there was no consistent change in the phase relation of these two legs (Table 1). In contrast, if the obstructed leg was a rear leg, protractions by the contralateral rear leg tended to be delayed (Table 1).

The separation of two peptides with hypertrehalosaemic activity from the corpus cardiacum of the Indian stick insect, Carausius morosus, was achieved by reversed-phase high-performance liquid chromatography using a Nucleosil C-18 column with a trifluoroacetic acid/acetonitrile gradient. The eluant was monitored at 210 nm and the hypertrehalosaemic activity was detected in ligated stick insects using a bioassay. In addition, the isolated material was potent in causing hyperlipaemia in migratory locusts and also in raising blood carbohydrates in the American cockroach. The amino-acid composition of the major peptide, hypertrehalosaemic factor II, was determined after acid hydrolysis with HCl or methanesulfonic acid. The analyses suggest that factor II is a nonapeptide which contains the following amino-acid residues: Asp, 2 Thr, Glu, Pro, Gly, Leu, Phe and Trp. This composition is almost identical to that of locust adipokinetic hormone I, lacking only one Asp residue.

Interjoint coordination is essential for proper walking behavior in multi-jointed insect legs. We have shown previously that movement signals from the femur-tibia (FT) joint can shape motor activity of the adjacent coxa-trochanter (CT) joint in the stick insect, Carausius morosus. Here, we present data on the role of position signals from the FT-joint on activity generated in motoneurons (MNs) of the CT-joint. We show that the probability of occurrence of stance (with depression in the CT-joint) or swing movements (with levation in the CT-joint) at the start of walking sequences is influenced by the angle of the FT-joint in the resting animal. We tested the influence of FT-joint angle on pharmacologically induced rhythmic activity of CT-joint depressor (DprTr) and levator (LevTr) MNs. The burst duration, mean spike rate within bursts, and duty cycle for each MN pool were found to depend on FT position. For LevTr MNs, these parameters progressively increased as the FT-joint was moved from extension to flexion, and the opposite was true for DprTr MNs. The cycle period of CT-MN rhythmicity also depended on FT position. In addition, we sometimes observed that the motor output shifted completely to one MN pool at extreme positions, suggesting that the central rhythm-generating network for the CT-joint became locked in one phase. These results indicate that position signals from the FT-joint modulate rhythmic activity in CT-joint MNs partly by having access to central rhythm generating networks of the CT-joint.

Two species of stick insects are currently known to be present in the Macaronesian archipelagos: Clonopsis gallica (Charpentier) (Phasmatodea: Bacillidae) on the Canary Islands and in the Azores and Carausius morosus (Sinéty) (Phasmatidae) in the Azores. Here, we provide the first reliable records of the presence and distribution of C. gallica and C. morosus on Madeira Island. Egg and adult stages are briefly described along with some notes on the life history of these species in captivity. Data on island-wide distribution are based on specimens donated by the public in response to an article published in a daily newspaper. This method of data collection raised great popular interest in stick insects. The role of newspapers as a means of communicating awareness in biodiversity issues is discussed.

A model of leg coordination in the stick insect, Carausius morosus

Like many flightless, obligatory walking insects, the stick insect Carausius morosus makes intensive use of active antennal movements for tactile near range exploration and orientation. The antennal joints of C. morosus have a peculiar oblique and non-orthogonal joint axis arrangement. Moreover, this arrangement is known to differ from that in crickets (Ensifera), locusts (Caelifera) and cockroaches (Blattodea), all of which have an orthogonal joint axis arrangement. Our hypothesis was that the situation found in C. morosus represents an important evolutionary trait of the order of stick and leaf insects (Phasmatodea). If this was true, it should be common to other species of the Phasmatodea. The objective of this comparative study was to resolve this question. We have measured the joint axis orientation of the head-scape and scape-pedicel joints along with other parameters that affect the tactile efficiency of the antenna. The obtained result was a complete kinematic description of the antenna. This was used to determine the size and location of kinematic out-of-reach zones, which are indicators of tactile acuity. We show that the oblique and non-orthogonal arrangement is common to eight species from six sub-families indicating that it is a synapomorphic character of the Euphasmatodea. This character can improve tactile acuity compared to the situation in crickets, locusts and cockroaches. Finally, because molecular data of a recent study indicate that the Phasmatodea may have evolved as flightless, obligatory walkers, we argue that the antennal joint axis arrangement of the Euphasmatodea reflects an evolutionary adaptation to tactile near range exploration during terrestrial locomotion.

In robotic assembly processes, detecting target pose is indispensable for robot manipulation algorithms. Such a tedious work hinders the further application of robot manipulation algorithms to real industrial processes. In this paper, a vision-based position/impedance control framework is proposed. Therein, the objective pose is firstly obtained by a motion capture system, where a kinematic equation is solved to Figure out the target assembly pose. Next the robot arm motion is approximated by an impedance model, in this way, the position/impedance control law of the robot is derived, which drives the robot to perform a compliant assembly manipulation. Finally, a memory stick assembly experiment is conducted on a 6-DOF robot arm equipped with a motion capture system and a force-torque sensor. Experiment shows the efficiency of the vision-based position/impedance hybrid controller in terms of autonomous positioning and compliant assembly. Due to its convenience and generality, the present controller can be expected to apply to more general industrial scenarios.

Classical engineering approaches to controlling a hexapod walker typically involve a central control instance that implements an abstract optimal gait pattern and relies on additional optimization criteria to generate reference signals for servocontrollers at all the joints. In contrast, the gait of the slow-walking stick insect apparently emerges from an extremely decentralized architecture with separate step pattern generators for each leg, a strong dependence on sensory feedback, and multiple, in part redundant, primarily local interactions among the step pattern generators. Thus, stepping and step coordination do not reflect an explicit specification based on a global optimization using a representation of the system and its environments instead they emerge from a distributed system and from the complex interaction with the environment. A similarly decentralized control at the level of single leg joints also may explain the control of leg dynamics. Simulations show that negative feedback for control of body height and walking direction combined with positive feedback for generation of propulsion produce a simple, extremely decentralized system that can handle a wide variety of changes in the walking system and its environment. Thus, there is no need for a central controller implementing global optimization. Furthermore, physiological results indicate that the nervous system uses approximate algorithms to achieve the desired behavioral output rather than an explicit, exact solution of the problem. Simulations and implementation of these design principles are being used to test their utility for controlling six-legged walking machines.