Docking Mechanism Research Articles

SPACECRAFT DOCKING DYNAMIC FEATURES BY USING A PERIPHERAL MECH-ANISM WITH ACCUMULATION OF APPROACH KINETIC ENERGY

Up to now, several docking systems have been developed under the International Docking System Standard (IDSS) by national space agencies and private companies. Docking mechanisms of these systems are based on different design and control principles. Thus a new peripheral docking mechanism, with more simple kinematics and design than that used in previous APAS docking unit, has been developed by Rocket and Space Corporation «Energia». An accumulation of spacecraft approach kinetic energy instead of traditional damping is used in this mechanism. It allows to move forward the docking ring for capture improvement and to ensure slowdown. Main features of spacecraft docking dynamic process with the use of this mechanism are described in this paper. Key words: spacecraft, docking mechanisms, docking dynamics.

Industrial Robotics for Spacecraft Rendezvous and Docking Simulation

It is to be expected that space robotics systems will develop more and more in the future spatial applications. One of the most challenging and risky missions for spacecraft is to perform autonomously Rendezvous and Docking (RvD) in space. This paper describes a hardware-in-the-loop RvD simulation facility which uses two ABB industrial robots to simulate the 6-DOF dynamic manoeuvring of the rendezvous process. Firstly, we also simulate the real robots and we deduce the kinematic and dynamic equations of space robotic system, then the trajectory is planned. The target motion is reduced only to the movement of the end-effector, but the chaser’s motion is based on the plan which solves the inverse kinematic equations, considering the movement limitations of the joints. Finally, a 3D simulation system was developed to evaluate the proposed method using Matlab/ Simulink environment. Simulation results verified the corresponding method and algorithms.

Impact of baseline IOP, vacuum, and different docking mechanisms, and their interaction on IOP rise in femtosecond laser–assisted refractive and cataract surgery

To study the intraocular pressure (IOP) variation during vacuum and docking of femtosecond laser application. Department for Ophthalmology, Kepler University Hospital, Johannes Kepler University Linz, Austria. Experimental study. Intracameral intraocular pressure (IOP) was monitored in 30 porcine exvivo models using a dual femtosecond laser platform (VICTUS). Five different baseline IOP levels (10 to 30mm Hg) were assessed during fluid-filled (liquid) docking, full-contact (applanating) docking, and vacuum application without docking. Raising the baseline intracameral IOP from 10 to 30mm Hg increased the IOP from 27.55mm Hg±5.93 (SD) to 56.85±6.10mm Hg in the fluid-filled docking group, and from 60.91±8.41mm Hg to 90.11±6.64mm Hg in the full-contact docking group. The full-contact docking procedure per se (excluding vacuum effect) increased the IOP by 61.7% (+36.58±5.84mm Hg). In contrast, fluid-filled docking (excluding vacuum effect) raised the IOP by only 3.1% (+0.72±2.71mm Hg). Each 5mm Hg reduction of baseline IOP resulted in a mean IOP reduction of 7.33±3.05mm Hg in the fluid-filled group, and 7.30±6.88mm Hg in the full-contact docking group (P<.001). Decreasing baseline intracameral IOP from 15 to 10mm Hg resulted in the highest IOP reduction between all subgroups (P<.01). Baseline IOP, docking procedures, and vacuum influenced IOP during femtosecond laser application in a synergistic manner. Lowering the baseline intracameral IOP resulted in a significantly lower IOP during fluid-filled docking for cataract surgery and full-contact docking for refractive surgery. Full-contact (applanating) docking resulted in a significantly higher IOP elevation compared with similar IOP values found during fluid-filled (liquid) docking and the application of the suction ring alone without docking.

Algorithm for Spacecraft Angular and Translational Motion Control with use of Orientation Thrusters

The paper discusses the algorithm of spacecraft orientation and docking thrusters control for simultaneous spatial and angular motion. The solution of control velocity formation problem and the problem of required engines configuration determination along with the optimization of control vector execution accuracy are considered. The formation of control velocity is carried out using a phase plane with switching lines and a zone of inactivity. The calculation of thrusters working duration time is based on the method of least squares with non-negative resulting solution vector and additional boundary conditions. In the paper, the necessary control parameters were chosen to ensure the necessary accuracy of spacecraft stabilization. To demonstrate the developed algorithm, mathematical modelling of various considered spacecraft's orbital flight stages was executed, including damping of initial angular velocities, spatial motion, and stabilization under the influence of continuous perturbations. The simulation took into account the disturbing moments acting on the spacecraft, thrusters mounting errors and the characteristics of the angular velocity meter. The elastic characteristics of the structure were not taken into account. The results of mathematical modelling showed that the proposed algorithm coped well with the task, and was able to ensure the movement of the spacecraft center of masses in a given direction and simultaneous angular stabilization with required accuracy.

Tube-based robust output feedback model predictive control for autonomous rendezvous and docking with a tumbling target

In this paper, a tube-based robust output feedback model predictive control method (TRMPC) is proposed for controlling chaser spacecraft docking with a tumbling target in near-circular orbit. The controller contains a simple, stable, Luenberger state estimator and a tube-based robust model predictive controller. Several practical challenges are also considered under dock-enabling conditions, such as the control saturation, velocity constraint, approach corridor constraint, and collision avoidance constraint. Meanwhile, uncertainties are carefully analyzed when designing the controller, including dynamics uncertainty, measurement error, and control deviation. The TRMPC ensures that all possible state trajectories with uncertainties lie in the minimum robust positively invariant set (mRPI, i.e., the so-called tube in this paper). The tube center is the solution of a nominal (without uncertainties) system. Another important contribution of this paper is to propose a technique where it is unnecessary to calculate the mRPI explicitly. Thereby, the ‘curse of dimensionality’ can be avoided for a six-dimensional system. To verify the feasibility of the proposed TRMPC strategy in the presence of uncertainties, two scenarios of autonomous rendezvous and docking (AR&D) are simulated. The simulation results show that the TRMPC method is more efficient in minimizing the uncertainties, fuel consumption, and computational cost, compared to the classic model predictive control (MPC) method.

Saturated adaptive output-constrained control of cooperative spacecraft rendezvous and docking

This paper investigates the robust relative pose control for spacecraft rendezvous and docking with constrained relative pose and saturated control inputs. A barrier Lyapunov function is used to ensure the constraints of states, so that the computational singularity of the inverse matrix in control command can be avoided, while a linear auxiliary system is introduced to handle with the adverse effect of actuator saturation. The tuning rules for designing parameters in control command and auxiliary system are derived based on the stability analysis of the closed-loop system. It is proved that all closed-loop signals always keep bounded, the prescribed constraints of relative pose tracking errors are never violated, and the pose tracking errors ultimately converge to small neighborhoods of zero. Simulation experiments validate the performance of the proposed robust saturated control strategy.

Research on High Availability Architecture of Cloud Platform

Cloud computing platforms have extremely requirements for high availability, and many solutions have proposed to ensure high availability of system. In view of the shortcomings of the existing solutions, we improve the high availability of the cloud computing platform based on the 3 tiers cluster environment, including the business layer cluster, the management cluster, and the main control layer. The management cluster ensures high availability of the service layer cluster. The main control layer ensures high availability of the management cluster. The main control layer uses the dock mechanism to ensure certain high availability. Through practical application, the solution achieves high availability of the cloud computing platform, achieving availability 99.99%.

An Autonomous Docking Mechanism for Vertical Lift Unmanned Aircraft

Abstract Unmanned aerial vehicles are increasingly being tasked to connect to payload objects or docking stations for the purposes of package transport or recharging. However, autonomous docking creates challenges in that the air vehicle must precisely position itself with respect to the dock, oftentimes in the presence of uncertain winds and measurement errors. This paper describes an autonomous docking mechanism comprising a static ring and actuated legs, coupled with an infrared tracking device for closed-loop docking maneuvers. The dock’s unique mechanical design enables precise passive positioning such that the air vehicle slides into a precise location and orientation in the dock from a wide range of entry conditions. This leads to successful docking in the presence of winds and sensor measurement errors. A closed-loop infrared tracking system is also described in which the vehicle tracks an infrared beacon located on the dock during the descent to landing. A detailed analysis is presented describing the interaction dynamics between the aircraft and the dock, and system parameters are optimized through the use of trade studies and Monte Carlo analysis with a three degree-of-freedom simulation model. Experimental results are presented demonstrating successful docking maneuvers of an autonomous air vehicle in both indoor and outdoor environments. These repeatable docking experiments verify the robustness and practical utility of the dock design for a variety of emerging applications.

Energy accumulator device for a new peripheral docking mechanism

The new peripheral docking mechanism is intended for docking with the International Standard-compliant docking ports. The distinct feature of this docking mechanism is accumulation, rather than damping of the kinetic energy of the approaching spacecraft. Selected as the basis for the kinematic system of the docking mechanism was Gough-Stewart. Design implementation of each of its translational links is hereafter called a rod. It consists of a ball screw converter, a gearbox and an energy accumulator. The new energy accumulating device includes a spiral spring mechanism and a controllable overrunning clutch, which can be commanded to disable or enable spinning of the spring mechanism shaft. The spring mechanism implements a predetermined non-linear load-deformation curve through the use of a variable-width ribbon in its design. The controllable overrunning clutch consists of a ratchet mechanism, friction (safety) brake and a two-position electromagnetic actuator, which makes it possible to control the switching of the clutch modes with short pulses, ensuring low power consumption and the ability to implement the specified sequence. Key words: spacecraft, peripheral docking mechanism, accumulation of mechanical energy.

Математическая модель динамики периферийного стыковочного механизма с накоплением кинетической энергии сближения космических аппаратов

The new peripheral docking mechanism is part of a docking unit designed in compli-ance with the International Docking System Standard (IDSS). The mechanism kinematics is based on the Gough-Stewart platform. Spring mechanisms are used for transformation of spacecraft approach kinetic energy. However, traditional damping is replaced by energy ac-cumulation. Therefore, the design includes new devices. The dynamic math model of the dock-ing mechanism described in this paper takes into account its main features – kinematics, inertia properties and generation of internal active forces by separate devices. Along with spacecraft motion equations and algorithms of docking unit contact interaction analysis, this model is part of a docking math model used for the analysis of kinematics and dynamics processes from the first contact to the end of retraction. Key words: spacecraft, docking mechanism, dynamics equations.

Recent developments in molecular docking technology applied in food science: a review

SummaryMolecular docking is a theoretical simulation method based on bioinformatics, which studies the interaction between molecules (such as ligands and receptors), and predicts their binding modes and affinity via a computer platform. This technology acts as a promising mean in medicinal chemistry such as structure‐based rational drug design, which is accepted by researchers in the scientific community. During recent years, various fundamental studies involving biomolecular interaction in the food matrix have gradually emerged. The remarkable advantages of molecular docking such as predicting experiments are attracting increasing attention for its application potential in various fields. This review presents the theory and software development of molecular docking, and emphasises its application in the field of food science, including nutritional components and food safety. Moreover, the operational mechanisms of molecular docking are further summarised in this review.

The Demonstrations of Flux Pinning for Space Docking of CubeSat Sized Spacecraft in Simulated Microgravity Conditions

The docking principle based on flux pinning is detailed and flux pinned docking mechanism (FPDM) is designed. In order to perform the space docking experiment on earth readily and cheaply, the simulated docking experimental platform (SDEP) with a FPDM is first designed and established. By performing the single docking experiment on the SDEP, the dynamic docking time response of FPDM is directly extracted by using the high-speed camera and the real-time tracking software TEMA. The analytical result of docking time response can assess whether the collision between two spacecraft modules of FPDM happens or not. Furthermore, the docking frequency response can be extracted based on Fast Fourier transformation. Based on the docking frequency response and the half-power method, the dynamic connection characteristics (connection stiffness, damping ratio, and damping coefficient) of FPDM can be calculated and analyzed, which estimates its performance. Based on the single docking experiment, the multiple docking experiments can be carried out to validate the reusable feasibility and to acquire connection characteristics of every time docking. The experimental demonstration system is designed and established in order to support future space docking for CubeSat sized spacecraft based on flux pinning and to accumulate some useful experimental datum.

Motion Planning on a Class of 6-D Lie Groups via a Covering Map

This paper presents an approach to motion planning for left-invariant kinematic systems defined on the six-dimensional frame bundles of symmetric spaces of constant cross-sectional curvature. A covering map is used to convert the original differential equation into two coupled equations each evolving on a three-dimensional Lie group. These lower dimensional systems lend themselves to a minimal global representation that avoids singularities associated with the use of exponential coordinates. Open-loop and closed-loop kinematic control problems are addressed to demonstrate the use of this mapping for analytical and numerical motion planning methods. The approach is applied to a spacecraft docking problem using two different types of actuation: 1) a fully actuated continuous low-thrust propulsion system; and 2) an underactuated single impulsive thruster and reaction wheel system.

Artificial Potential Function Safety and Obstacle Avoidance Guidance for Autonomous Rendezvous and Docking with Noncooperative Target

The problem of artificial potential function (APF) safety and obstacle avoidance guidance for autonomous rendezvous and docking of chaser spacecraft with noncooperative spacecraft is studied. The relative motion equation of the chaser and the target is established based on the line-of-sight coordinate system, the reference state is designed, and the corresponding state error is deduced. The attitude motion equation of the noncooperative target spacecraft in space is established. The safety and obstacle avoidance guidance problem of autonomous rendezvous and docking with noncooperative target is transformed into a path planning problem in a dynamic environment. The attractive potential function is designed according to the state error. In order to ensure that the chaser can safely approach the noncooperative target spacecraft, a safe corridor with ellipse cissoid is designed in the final approaching stage of autonomous rendezvous and docking. The obstacle is assumed to be a sphere with a certain radius to avoid its influence in the approach, and the obstacle potential function is designed based on the Gaussian function method. The total potential function of the system is designed according to the attractive potential function, the safe potential function, and the obstacle potential function. The total potential function of the system is modified to ensure that the reference state is the minimum of the total potential function of the system. The stability of the system is proven according to the Lyapunov stability principle, and the conditions for satisfying the monotonic decrease in the total potential function of the system are deduced. Finally, the effectiveness of the proposed method is verified by three sets of numerical simulations.

Fibrinogen binding is affected by amino acid substitutions in C-terminal repeat region of fibronectin binding protein A

Fibronectin-binding protein A (FnBPA), a protein displayed on the outer surface of Staphylococcus aureus, has a structured A-domain that binds fibrinogen (Fg) and a disordered repeat-region that binds fibronectin (Fn). Amino acid substitutions in Fn-binding repeats (FnBRs) have previously been linked to cardiovascular infection in humans. Here we used microtiter and atomic force microscopy (AFM) to investigate adhesion by variants of full-length FnBPA covalently anchored in the outer cell wall of Lactococcus lactis, a Gram-positive surrogate that otherwise lacks adhesins to mammalian ligands. Fn adhesion increased in five of seven FnBPA variants under static conditions. The bond targeting Fn increased its strength with load under mechanical dissociation. Substitutions extended bond lifetime (1/koff) up to 2.1 times for FnBPA-Fn. Weaker adhesion was observed for Fg in all FnBPA variants tested with microtiter. However, mechanical dissociation with AFM showed significantly increased tensile strength for Fg interacting with the E652D/H782Q variant. This is consistent with a force-induced mechanism and suggests that the dock, lock, and latch (DLL) mechanism is favored for Fg-binding under mechanical stress. Collectively, these experiments reveal that FnBPA exhibits bimodal, ligand-dependent adhesive behavior. Amino acid substitutions in the repeat-region of FnBPA impact binding to both ligands. This was unexpected for Fg since all variants have the same A-domain sequence, and the Fg-binding site is distant from the repeat region. This indicates that FnBRs may fold back on the A-domain in a way that impacts the DLL binding mechanism for Fg.

Deep insights into the organic carbon role in selectivity and adsorption mechanism of phosphate and crystal violet onto low–cost black limestone: Modelling and physicochemical parameters interpretation

Herein, raw black limestone (RBL) and its activated form at 450 °C/5 h (ABL) were characterized and tested as adsorbents for phosphate and crystal violet (CV) at pH (2.0–10.0). The two adsorbents displayed nearly the same efficiency for phosphate uptake, while RBL was more effective for CV. Isotherm studies at 298–318 K indicated that Langmuir, Freundlich, and Dubinin–Radushkevich models described well the uptake results without determination of the physicochemical parameters governing phosphate and CV adsorption mechanisms. The application of five advanced statistical models (ASM) indicated that monolayer with one energy and monolayer with two energies fitted well the phosphate and CV adsorption, respectively. Phosphate adsorption was controlled by multi–docking mechanism, while multi–docking and multi‒molecular mechanisms were involved in CV uptake onto the RBL. The density of receptor sites (NM) was resulted to be an important factor controlling the phosphate and CV adsorption capacities. With temperature, the NM values increased from 149.62 to 215.52 mg/g and decreased from 340.13 to 208.97 mg/g for phosphate and CV, respectively. This confirmed the significant role of organic carbon interactions as n–π and π–π in enhancement of CV uptake. The adsorption energies exhibited the physical nature of the adsorption processes as endothermic and exothermic reactions for phosphate and CV, respectively. Thermodynamic studies confirmed the spontaneous nature of the phosphate and CV adsorption onto RBL. Based on this study, it can be concluded that RBL is an excellent and low–cost adsorbent for water contaminants, especially organic dyes. Furthermore, the interpretations of steric and energetic parameters indicated that the adsorption performance of RBL is mainly related to its organic carbon content.

Docking mechanism design and dynamic analysis for the GEO tumbling satellite

Purpose According to the requirements of servicing and deorbiting the failure satellites, especially the tumbling ones on geosynchronous orbit, this paper aims to design a docking mechanism to capture these tumbling satellites in orbit, to analyze the dynamics of the docking system and to develop a new collision force-limited control method in various docking speeds. Design/methodology/approach The mechanism includes a cone-rod mechanism which captures the apogee engine with a full consideration of despinning and damping characteristics and a locking and releasing mechanism which rigidly connects the international standard interface ring (Marman rings, such as 937B, 1194 and 1194A mechanical interface). The docking mechanism was designed under-actuated, aimed to greatly reduce the difficulty of control and ensure the continuity, synchronization and force uniformity under the process of repeatedly capturing, despinning, locking and releasing the tumbling satellite. The dynamic model of docking mechanism was established, and the impact force was analyzed in the docking process. Furthermore, a collision detection and compliance control method is proposed by using the active force-limited Cartesian impedance control and passive damping mechanism design. Findings A variety of conditions were set for the docking kinematics and dynamics simulation. The simulation and low-speed docking experiment results showed that the force translation in the docking phase was stable, the mechanism design scheme was reasonable and feasible and the proposed force-limited Cartesian impedance control could detect the collision and keep the external force within the desired value. Originality/value The paper presents a universal docking mechanism and force-limited Cartesian impedance control approach to capture the tumbling non-cooperative satellite. The docking mechanism was designed under-actuated to greatly reduce the difficulty of control and ensure the continuity, synchronization and force uniformity. The dynamic model of docking mechanism was established. The impact force was controlled within desired value by using a combination of active force-limited control approach and passive damping mechanism.

Monocular Vision-Based Pose Determination in Close Proximity for Low Impact Docking.

Pose determination in close proximity is critical for space missions in which monocular vision is one of the most promising solutions. Although numerous approaches such as using artificial beacons or specific shapes on spacecrafts have proved to be effective, the high individuation and the large time delay limit their use in low impact docking. This paper proposes a unified framework to determinate the relative pose between two docking mechanisms by treating their guide petals as measurement objects. Fusing the pose information of one docking mechanism to simplify image processing and creating an intermediate coordinate system to solve the perspective-n-point problem greatly improve the real-time performance and the robustness of the method. Experimental results show that the position measurement error is within 3.7 mm, while the rotation error around docking direction is less than 0.16°, corresponding to a measurement time reduction of 85%.

Choice of energy accumulator parameters for a new peripheral docking mechanism

Spacecraft docking is a controlled on-orbit mechanical assembly process realized using active and passive docking units. The docking mechanism of the active unit provides capture conditions, attenuation of active spacecraft approach energy, alignment and retraction of the docking units before their hard connection. A kinematical scheme of a new peripheral docking mechanism is considered in this paper. Instead of energy damping, it is based on energy accumulation using springs with controlled recoil blocking. The blocking is activated before docking and keeps the docking mechanism in its initial position. On the first contact signal, the blocking is switched off releasing the energy of compressed springs for quick forward moving of the docking ring and improving capture. The blocking is activated again after capture and approach energy is accumulated by the springs without returning to the mechanical system. Avoiding contacts of docking mechanism links between each other and with the docking unit body is important for peripheral mechanisms due to their design. A procedure for choosing parameters of an energy accumulator that allows attenuating a max permissible energy without link contacts and without exceeding the max permissible value of the axial interface load is considered here. Key words: spacecraft, docking, docking mechanism.

Cyclin-Specific Docking Mechanisms Reveal the Complexity of M-CDK Function in the Cell Cycle.

SummaryCyclin-dependent kinases (CDKs) coordinate hundreds of molecular events during the cell cycle. Multiple cyclins are involved, but the global role of cyclin-specific phosphorylation has remained unsolved. We uncovered a cyclin docking motif, LxF, that mediates binding of replication factor Cdc6 to mitotic cyclin. This interaction leads to phospho-adaptor Cks1-mediated inhibition of M-CDK to facilitate Cdc6 accumulation and sequestration in mitosis. The LxF motif and Cks1 also mediate the mutual inhibition between M-CDK and the tyrosine kinase Swe1. Additionally, the LxF motif is critical for targeting M-CDK to phosphorylate several mitotic regulators; for example, Spo12 is targeted via LxF to release the phosphatase Cdc14. The results complete the full set of G1, S, and M-CDK docking mechanisms and outline the unified role of cyclin specificity and CDK activity thresholds. Cooperation of cyclin and Cks1 docking creates a variety of CDK thresholds and switching orders, including combinations of last in, first out (LIFO) and first in, first out (FIFO) ordering.