In order to verify the task-specific performance of the chosen manipulator length and configuration, the kinematics of the manipulator were validated and analyzed using the method of the reachability map (Porges et al., 2014). The reachability map is a hierarchically discretized robot workspace model. The main processing flow starts with a predicted pose that must be initially provided by means of robot kinematics and trajectory planning. Note that the robot needs to provide the necessary internal structural forces in order to keep the chaser in its position relative to ENVISAT, given that the chaser GNC is assumed to be switched off.
Note that in order to minimize flexibility effects, the velocity of the commanded arm trajectory can be reduced. It was determined that by far the least stiff element was the LAR itself, and therefore that a longer clamping arc equated to a stiffer system, as the clamping mechanism essentially acts as a local doubler. In this regard, the performance of the visual tracking is very important, as it is the most important contributor to the positioning accuracy of the robotic arm and therefore, also defines the worst case positioning error in translation and rotation as design drivers for both, the gripper and the clamping mechanism. This approach eliminates the need for cameras imaging the clamping system and does not require teleoperation. Unit quaternions are closed under multiplication, but not under addition. The solar array launch restraints could also have worked due to their exposed location on ENVISAT, but it was decided that the LAR ring provided a more exposed interface for the majority of satellites, therefore making the LAR clamping system solution more commercially attractive for satellite servicing missions.
Облекчаване На Болката В Реално Време
At the base of the clamping subsystem is an alignment mechanism, consisting of a rotary joint that can pitch the clamping mechanism relative to the chaser axis through approximately 120deg. In addition to a redundant motor, geartrain and brake, the mechanism also incorporates a 16bit output rotary position sensor that allows for precision sensing of the absolute position and allows position control to an accuracy of 0.05deg. This mechanism is initially used to deploy the system from its stowed launch configuration. On the other hand, the thrusters action to control the base can impact on the arm end effector positioning accuracy. Reachability maps can be applied beyond the scope of analysis, for example, an on-line determination of robot base pose while performing a grasping operation. Within the dark blue area, the end-effector has an optimal manipulability for grasping from any direction.
Validation is performed by querying the reachability map for existence of the target end-effector pose, and maximizing the reachability index which in turn maximizes the ability of the robot to rotate the end-effector. In other words, the reachability index reflects what portion of SO(3) space is reachable within a small volume of R3 space. на какъв лекар се ходи за болки в кръста
. Green volumes indicates feasible and red undesired reachability index values. Visualizing all information stored in the reachability map is not feasible. Since ENVISAT’s CoM position is not exactly known, the ability to adjust the pitch angle between the two spacecraft allows for thrust vector corrections as required. Notice that Γ acts as an internal damping torque and it will not interfere with the end effector motion.
After successful capture of the target with the robotic arm, the chaser is moved into position by the arm such that the LAR is brought within the jaws. When tripped, these sensors initiate an autonomous operation to close the jaws onto the LAR ring. For trade (1), an integrated performance analysis of the robotic system after ENVISAT capture was performed, to determine the achievable arm tip positioning accuracy, and therefore LAR positioning accuracy, for a blind autonomous capture, using only proximity sensors to detect the LAR in the capture box. Figure 7. Effects of the link flexibility for a 60s transitioning maneuver: joint torques (Top, Left), positioning error of the clamping interface due to flexible displacements (Top, Right) and overview of modeled arm elements (Bottom): flexible links (orange), rigid links (gray), rigid gripper (blue). The arm segments which enclose the joint drives and the gripper were modeled as rigid.
This is equivalent to the moment in which the last joint of the robot has to apply, which is dependent on the choice of the arm delivery point position. The tool enables the assesment of the structural eigenfrequencies, as well as the tracking error induced by the flexibility when commanding representative joint trajectories. Amongst the two remaining options, the LAR was selected because it is rigid, strong, and its geometry is well known. Once the LAR had been selected as the clamping interface, two key design trades in the design of the clamping mechanism consisted of: (1) The size of the capture envelope: the size and mass of the clamp, vs. This allows uploading computer-aided design models of the robot and of ENVISAT, as well as positioning Sun and Earth in relation to the two satellites in any realistic fashion.
This analysis shows that the effects of the link flexibility on the end-effector position are well within the clamping mechanism structural design requirements. To analyze the effects of intrinsic flexibility in the mechanical structure of the arm, a multi-body simulation was set up in the commercial simulation tool SIMPACK®, featuring free-floating target and chaser satellites, as well as a flexible model of the robotic manipulator. The final design of the clamping mechanism consists of a set of motor-actuated parallel jaws with passively compliant clamping fingers and rollers that conform to the profile of the LAR ring as they close on the structure, creating a very stiff connection between the two spacecraft. In total, 120 sequences were used, related to two different tumbling states of ENVISAT (defined by the initial angular velocity of 5deg/s around the y and z-axis, respectively), 10 different start times for the robot approach maneuver (this guarantees that each of the ten sequences start with different initial orientations with respect the given Sun position and as such different illumination conditions), and 6 sunlight directions (for the three Cardinal directions, in the positive or in the negative sense).
Avis Client (2)
Съхранява здравето на ставите
Note also, that the case of target initial angular velocity about the body-fixed z-axis (stable, since maximum axis of inertia), yield torque values below 80 Nm. Furthermore, ωt and ω°t are ENVISAT’s angular velocity and acceleration, respectively. Due to the clamping subsystem securing along the circumference of the ENVISAT’s LAR, the thrust vector naturally intersects ENVISAT’s center line in the y-z plane. ENVISAT’s centre of mass (we neglect the mass of the chaser, for simplicity), respectively. All of these make it an ideal interface for the clamping mechanism. болки в кръста от изстиване
. Figure 6. Capability map cross-sections of satellite-mounted manipulator with chaser in arm delivery point for the bottom (Top Left and Top Middle) and top (Bottom, left) approach, as well as in clamping position (Top Right).