Monocular Visual-Inertial and Robotic-Arm Calibration in a Unifying Framework

Reliable and accurate calibration for camera,inertial measurement unit(IMU)and robot is a critical prerequisite for visual-inertial based robot pose estimation and surrounding environment perception.However,traditional calibrations suffer inaccuracy and inconsistency.To address these problems,this paper proposes a monocular visual-inertial and robotic-arm calibration in a unifying framework.In our method,the spatial relationship is geometrically correlated between the sensing units and robotic arm.The decoupled estimations on rotation and translation could reduce the coupled errors during the optimization.Additionally,the robotic calibration moving trajectory has been designed in a spiral pattern that enables full excitations on 6 DOF motions repeatably and consistently.The calibration has been evaluated on our developed platform.In the experiments,the calibration achieves the accuracy with rotation and translation RMSEs less than 0.7°and 0.01 m,respectively.The comparisons with state-of-the-art results prove our calibration consistency,accuracy and effectiveness.

Spiral trajectories induced by radial thrust with applications to generalized sails

In this study,new analytical solutions to the equations of motion of a propelled spacecraft are investigated using a shape-based approach.There is an assumption that the spacecraft travels a two-dimensional spiral trajectory in which the orbital radius is proportional to an assigned power of the spacecraft angular coordinate.The exact solution to the equations of motion is obtained as a function of time in the case of a purely radial thrust,and the propulsive acceleration magnitude necessary for the spacecraft to track the prescribed spiral trajectory is found in a closed form.The analytical results are then specialized to the case of a generalized sail,that is,a propulsion system capable of providing an outward radial propulsive acceleration,the magnitude of which depends on a given power of the Sun-spacecraft distance.In particular,the conditions for an outward radial thrust and the required sail performance are quantified and thoroughly discussed.It is worth noting that these propulsion systems provide a purely radial thrust when their orientation is Sun-facing.This is an important advantage from an engineering point of view because,depending on the particular propulsion system,a Sun-facing attitude can be stable or obtainable in a passive way.A case study is finally presented,where the generalized sail is assumed to start the spiral trajectory from the Earth’s heliocentric orbit.The main outcome is that the required sail performance is in principle achievable on the basis of many results available in the literature.

Analytical solution to logarithmic spiral trajectories with circumferential thrust and mission applications

This study made use of a shape-based method to analyze the orbital dynamics of a spacecraft subject to a continuous propulsive acceleration acting along the circumferential direction.Under the assumption of a logarithmic spiral trajectory,an exact solution to the equations of motion exists,which allows the spacecraft state variables and flight time to be expressed as a function of the angular coordinate.There is also a case characterized by specific initial conditions in which the time evolution of the state variables may be analytically determined.In this context,the presented solution is used to analyze circle-to-circle trajectories,where the combination of two impulsive maneuvers and a logarithmic spiral path are used to accomplish the transfer.The determined results are then applied to the achievement of the Earth–Mars and the Earth–Venus transfers using actual data from a recent thruster developed by NASA.