The gripper design was developed by OHB and is oriented toward the LAR geometry and mechanical properties which are of type ACU 2624. Due to the requirement of grasping the LAR from the outside, and it having a cylindrical, foil-covered surface with only a small extrusion (less than 4 mm in thickness) for vertical fixation, a classical hinge-like approach was found to be inconvenient to achieve the desired 6-DoF force closure. Furthermore, the three DOF of orientation of the base-spacecraft are either not actively controlled or controlled only by momentum-exchange devices. The effects of manipulator operations on the orientation and position of the Shuttle orbiter and the ISS have been small and could be managed through operational procedures (Sargent, 1984). For fast-moving manipulators mounted on small base-spacecraft, the position and orientation disturbances due to manipulator motion become critical, as demonstrated on ETS-VII and Orbital Express (Oda, 2000; Kennedy, 2008). Hence, the engineers developing the spacecraft control system, specifying the sensor systems to be used, developing the communications system, and developing the operations plan must have an understanding of the complex dynamics arising from the multi-body system.
Figure 6A shows the comparison of the norm of the change of the center of mass of the system with respect to its initial position as a function of time. A comprehensive overview of methods to account for the dynamic coupling in controlling the position and orientation of both the end-effector of the manipulator and the base-spacecraft is provided in Flores-Abad et al. The orientation of this joint equals the orientation of the base-spacecraft in inertial space. A spacecraft-manipulator system is here defined to be rotation-floating when maneuvering in a 3 DOF under-actuated mode, in which both the DOF at the manipulator’s joints and the three DOF of orientation of the base-spacecraft are controlled by internal torques only.
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The maneuvering cases here defined as floating and rotation-floating have in previous literature been referred to as free-floating. The analysis and simulation of floating, rotation-floating and rotation-flying maneuvering modes can be typically conducted with good accuracy as if the system was isolated. A spacecraft-manipulator system is here defined to be flying when maneuvering in a mode in which all of the DOF at the manipulator joints are actively controlled by joint motor torques and the six DOF of motion of the base-spacecraft are actively controlled by external forces, provided typically by reaction jet thrusters.
The base-spacecraft translation is controlled by external forces, provided typically by reaction-jet thrusters. The rotation of the base-spacecraft is controlled only by external torques (typically provided by reaction-jet thrusters). Since, in the absence of external forces, the system center-of-mass remains stationary, the complex free-floating system is replaced by a dynamically consistent fixed-base system. The spacecraft-manipulator system can maneuver in different modes, typically designated by the terms free-floating and free-flying (Umetani and Yoshida, 1989; Dubowsky and Papadopoulos, 1993). To arrive at a more detailed and complete classification of spacecraft maneuvering modes, the authors propose to add three modes, thus fully covering all possible spacecraft maneuvers (see Table 1). The new modes are defined for an isolated spacecraft-manipulator system operating in pure weightlessness and in the absence of friction. This is typically achieved by reaction-jet thrusters firing in couples, thus generating a pure torque with total null force. пронизваща болка в гърба
. The Lagrangian method is thus used to explain the development of the equations of motion in the present paper, due to its systematic nature.
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A general description of the Newton-Euler method is given in Siciliano et al. The fundamental advantage of the Newton-Euler approach is its computational efficiency as a recursive algorithm. The novel areas that can help differentiate a design from its peers, determined by an absence in the literature or a notable lack of recent improvement, have been here listed. The tutorial presented here uses the Lagrangian method for a single manipulator mounted on a base-spacecraft, under the assumption of zero linear and angular momenta, which makes it applicable to the description of the majority of current spacecraft-manipulator systems. A spacecraft-manipulator system is here defined to be floating when maneuvering in a six DOF under-actuated mode in which only the manipulator joints are actively controlled. The system moves only under the effect of the internal reactions due to the actuation of the manipulator’s joint motors. Once the target is captured, the underlying conditions to detumble the newly formed chaser-target system are met, and a completely detumbled system is achieved once the manipulator’s motion is gradually stopped shortly after.
The new contributions of this work, which are appearing for the first time in literature to the best knowledge of the authors, are: (1) the formulation and design of a simultaneous capture and detumble maneuver, and (2) the demonstration of the proposed maneuver’s feasibility via extensive numerical simulations and hardware-in-the-loop experiments. To the authors’ knowledge, this is the first time that the Generalized Jacobian approach is derived in completeness, drawing from multiple references in literature and the authors’ own research. Available literature focusses on the application and performance analysis of various approaches to describing the coupled dynamics of a spacecraft-manipulator system (Moosavian and Papadopulos, 2007; Flores-Abad et al., 2014), but does not provide a complete description of the modeling approach that would allow an aerospace engineer to access the topic without consulting a combination of research publications and textbooks. However, multi-body dynamics and modeling of robotic systems are not part of a typical undergraduate aerospace engineering curriculum and are rarely covered in aerospace engineering graduate programs.
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For the extension of this approach to multi-manipulator systems, the reader is referred to Moosavian and Papadopoulos (2004), while the equations of motion of a spacecraft-manipulator system with non-zero angular momentum is covered in Nanos and Papadopoulos (2011). This complete discussion of the GJM approach enables the computation of symbolic expressions of the spacecraft-manipulator system equations of motion, which can then be used for the formulation of guidance and control laws in addition to numerical simulations. For a prismatic joint, the parameter di is variable and identical to the joint extension. The three DOF of translation of the system center-of-mass are not actively controlled. The manipulator DOF are controlled by joint motor torques.
D’Ambrosia R. The Ilizarov technique. Orthopedics 1989;12:495. Medline, ISI, Google Scholar
Evaluation of Numerical Performance
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Since the dynamics between the manipulator and the base-spacecraft are coupled, the system requires an integrated control system to meet the capture or manipulation goals and ensure mission success. A second important contribution of the paper is the introduction of a new, more accurate and detailed categorization for spacecraft-manipulator control modes. болки в кръста в седнало положение
. Since the base spacecraft in one of the five maneuvering modes described in section Detailed Classification of Spacecraft-Manipulator System Maneuvering, and thus not fixed in space, any motion of the manipulator will cause a rotation and translation of the base spacecraft. Section Detailed Classification of Spacecraft-Manipulator System Maneuvering provides a detailed classification of the maneuvering modes of a spacecraft-manipulator system. The results of sample simulations are reported in section Numerical Simulations. Moreover, the complex dynamics of the spacecraft-manipulator system must be accounted for in the maneuver planning and in its overall maneuver timeline. The Lagrangian method develops the equations of motion of a multibody system from its kinetic and potential energies, using a set of generalized coordinates describing the positions of the links (Siciliano et al., 2010). Following Siciliano et al.