Kui Sun

Ground verification of space robot capturing the free-floating target based on visual servoing control with time delay

Purpose – The purpose of this paper is to solve the ground verification and test method for space robot system capturing the target satellite based on visual servoing with time-delay in 3-dimensional space prior to space robot being launched. Design/methodology/approach – To implement the approaching and capturing task, a motion planning method for visual servoing the space manipulator to capture a moving target is presented. This is mainly used to solve the time-delay problem of the visual servoing control system and the motion uncertainty of the target satellite. To verify and test the feasibility and reliability of the method in three-dimensional (3D) operating space, a set of ground hardware-in-the-loop simulation verification systems is developed, which adopts the end-tip kinematics equivalence and dynamics simulation method. Findings – The results of the ground hardware-in-the-loop simulation experiment validate the reliability of the eye-in-hand visual system in the 3D operating space and prove the...

The ground-based verification system of visual servoing control for a space robot

Owing to the high cost and risks of robotic tasks in space, space robots require that all procedures should be strictly verified and tested before launching. A ground-based multi-loop simulation verification testbed has been developed which can validate and test the visual servoing system for free-floating space robot to capture the target satellite in 3-dimensional space. The verification testbed which includes the real hardware and the simulation software adopts the method of kinematics equivalence and multi-loop simulation. Finally, the multi-loop simulation experimental results demonstrate the effectness of the ground verification testbed and validate the correctness and accuracy of the eye-in-hand visual servoing system in the 3-dimensional space.

Design and experiment of a universal space-saving end-effector for multi-task operations

Purpose – The purpose of this paper is to present the design and experiment of a universal space-saving end-effector for multi-task operations. Design/methodology/approach – The universal end-effector is equipped with capture and actuation transmission capabilities with two corresponding subsystems, which are highly integrated systems of mechanics, electronics and sensors. A trefoil-shaped capture system is developed for closed envelop. The worm gear pair is adopted for self-locking and space-saving, and it is used in a unique manner for three grapple chains’ synchronous motion. The combination of optimal straight path linkage and pantograph mechanism is proposed in the transmission system. The electrical structure and the multi-sensory system provide the foundation for control strategy. Findings – Simulations and experiments demonstrated characteristics of the universal end-effector. The compliance of the manipulator guaranteed the achievement of “soft capture” by the end-effector. Due to the self-lockin...

Development of ground experiment system for space end-effector capturing the floating target in 3-dimensional space

Purpose – The purpose of this paper is to develop a set of ground experiment system to verify the basic functions of space effector and the capturing reliability of space end-effector for the free-floating target payload in the three-dimensional space. The development of ground experiment system for space end-effector is essential and significant, because it costs too much to launch a space robot or other spacecraft and carry out operation tasks in space. Owing to the negligible gravity in space, which is different from that in the ground environment, ground experiment system for space end-effector should have the capability of verifying the basic functions of space effector and the reliability of space end-effector in capturing the free-floating target payload in space. Design/methodology/approach – The ground experiment system for space end-effector mainly adopts the hybrid simulation method, which includes the real hardware experiment and software simulation. To emulate the micro-gravity environment, t...

DSP/FPGA-based highly integrated flexible joint robot

This paper presents a DSP/FPGA based multi-sensory flexible-joint robot including modular mechanics, hardware and software architecture. The robot is composed of four modular flexible joints and a DLR-HIT-Hand. In each joint there is a Field Programmable Gate Array (FPGA) for sensor data processing, brushless DC motor control and communication. The kernel of the hardware system is a PCI-based high speed floating-point Digital Signal Processor (DSP) for the arm/hand Cartesian level control, and FPGA for two high speed (up to 25 Mbps) real-time Serial Buses communication with the arm and hand. All the electronics are integrated into the joint to achieve the high modularity and reliability. Cartesian impedance control and position control with on-line gravity compensation are realized for regulation tasks of the robot with elastic joints. In addition, the experiments of the joint impedance control and Cartesian impedance control demonstrate that the multi-sensors highly integrated robot has a good performance.

Ground micro-gravity verification of free-floating non-cooperative satellite docking

Ground micro-gravity verification and test for the on-orbit docking operation of non-cooperative target satellites in 3-dimensional space based on two 6-DOF industrial robots is essential and significant owing to the high risk and cost and the influence of the earth gravity. The development of ground micro-gravity verification system mainly adopts the hybrid simulation method, which includes the real contact hardware test experiment and the virtual software simulation. To realize the emulation of ground micro-gravity environment, the gravity compensation algorithm of the non-cooperative target satellites is necessary in the system. The admittance control method is adopted to realize the soft docking function to ensure the success of the docking mission, which mainly simulates the real contact force and the real motion state during the docking process in space. The ground verification experiment results show that servicing satellite can successfully dock or capture the free-floating non-cooperative target satellites in 3-dimensional space.

Pose measurement of nozzle based on laser range finders for capturing satellite

Sensors system is considered as one of the most indispensable devices to the mission of capturing a satellite for on-orbit servicing in the space. In this paper, in order to measure the pose of nozzle, six laser range finders are installed in the capturing nozzle device for entering into and capturing nozzle, and a Geometric Axis Approximation (GAA) method is proposed to estimate the pose of satellite nozzle. Six laser range finders are arranged in the configuration of emission radiated at two planes of top and bottom. The pose measurement system is composed of the six laser range finders, applicable for real-time measurement of the ranges from inner surface of nozzle. Based on the properties of nozzle shape and finders arrangement, the GAA method is used to estimate the pose of nozzle by a connecting line between two centers of circles in the top and bottom planes. In the pose estimation of GAA method, solving the nonlinear transcendental equations can be avoided and a simple explicit model is built. Therefore, the GAA method is suitable for real time measurement. In this paper, the theoretical error of GAA method is analyzed, and in the capturing nozzle experiment system, the experiments of pose measurement are carried out. The results of experiments prove the efficiency of GAA method in pose estimation to nozzle based on laser range finders.

Development of HIT Humanoid Robot

This paper gives an overview on HIT humanoid robot, which is developed as a research platform for replicating human in special environments. The system has two upper extremities, each upper extremity includes a 7-DOF humanoid arm and a 15-DOF dexterous hand as end-effector. Two humanoid arms and dexterous hand are combined with a 2-DOF dynamic torso and a 3-DOF binocular head to form the humanoid upper body. A wheeled mobile robot is employed to provide mobility. In this paper, we describe the design specification and give an overview on mechanical design of each subsystem. Additionally, we give a short introduction to the hardware architecture and software of HIT humanoid robot.

Stability analysis and control in the process of floating-target capture with hardware-in-the-loop system

Purpose The purpose of this paper is to develop an easily implemented and practical stabilizing strategy for the hardware-in-the-loop (HIL) system. As the status of HIL system in the ground verification experiment for space equipment keeps rising, the stability problems introduced by high stiffness of industrial robot and discretization of the system need to be solved ungently. Thus, the study of the system stability is essential and significant. Design/methodology/approach To study the system stability, a mathematical model is built on the basis of control circle. And root-locus and 3D root-locus method are applied to the model to figure out the relationship between system stability and system parameters. Findings The mathematical model works well in describing the HIL system in the process of capturing free-floating targets, and the stabilizing strategy can be adopted to improve the system dynamic characteristic which meets the needs of the practical application. Originality/value A method named 3D root-locus is extended from traditional root-locus method. And the improved method graphically displays the stability of the system under the influence of multivariable. And the strategy that stabilize the system with elastic component has a strong feasible and promotional value.

Pose measurement of robot arm end based on laser range finders

A pose measurement system based on laser range finders for robot is proposed to measure the pose of target for robot arm manipulating. Laser range finder for robot is developed based on the triangulation ranging theory, which is highly integrated with a wide range and a shorter minimum measurement range. The system of pose measurement, three-dot measuring, is composed of three laser range finders emitting three parallel laser beams, which is used to measure the pose of plat surface. 3-degree of freedom of one range and two pose angles can be measured by the system. The method of pose measurement is practical and simple with high speed and low cost software and hardware. The experiment of pose measurement in the robot arm is carried out. The results show that the pose measurement based on three laser range finders is feasible.