Fengshui Jing

Nonlinear robust control method for active vibration isolation using a Stewart platform

This paper focuses on developing a nonlinear robust controller to solve the active vibration isolation problem using a Stewart platform. The dynamics of the Stewart platform driven by voice coil actuators is derived by the Newton-Euler method. The influence factors of vibration isolation are taken into account, such as the nonlinear characteristics of the dynamic model, the parameter perturbation and the unmodeled dynamics, etc. The favorable feature of the proposed controller is that it is not necessary for the upper bound of the unmatched uncertainties to be known in advance. A tuning rule is designed to deal with the estimation problem of the uncertainties. The uniformly ultimately bounded (UUB) stability of the controller is demonstrated by applying the Lyapunov approach and a UUB lemma. The simulation results illustrate that the controller can effectively attenuate low frequency vibrations in all six degrees of freedom (DOFs) and the satisfactory vibration isolation performance can be achieved.

Anti-crosswind Autolanding of UAVs based on Active Disturbance Rejection Control

The safe landing of unmanned aerial vehicles (UAVs) under various wind conditions has been a challenging task for decades. As the first step of landing, the longitudinal landing control has been well researched. But the lateral landing control, which is the second step of landing, is still facing a lot of challenges especially in crosswind conditions. In this paper, a UAV with wide span is researched. Due to its wide span, its wing tips may possibly touch the ground if the wings are not level at touchdown. An autolanding control scheme which consists of a longitudinal autolanding control system and a lateral autolanding control system is designed based on the Active Disturbance Rejection Control (ADRC) to enable the UAV to land safely in crosswind. The longitudinal autolanding control system is composed of a throttle control subsystem and an altitude control subsystem. The lateral autolanding control system is composed of a crabbing control subsystem and a decrabbing control subsystem. In contrast to previous methods, our approach can directly and real-timely estimate the UAV’s internal and external disturbances (e.g., system’s longitudinal and lateral couplings, wind disturbances) and then compensate for them. Simulations are done from the glide phase to the parking at the end of taxiing under wide range wind disturbances (e.g., constant crosswind, changing crosswind). Results show that our autolanding control scheme can land the UAV safely under wide range crosswind with the help of ADRC.

Automatic takeoff of unmanned aerial vehicle based on Active Disturbance Rejection Control

The safe takeoff of unmanned aerial vehicles (UAVs) under various wind conditions has been a challenging research for decades. We design an automatic takeoff control system based on the Active Disturbance Rejection Control (ADRC). The automatic takeoff control system consists of a taxiing control subsystem, an attack angle control subsystem, a pitch angle control subsystem, and a smooth switch control subsystem whose function is to switch the forenamed three subsystems smoothly without the jumps of the elevator actuator. In contrast to previous methods, our approach can directly and real-timely estimate the UAVs internal and external disturbances and then compensate for them. Simulation results show that our automatic takeoff control system can lead the UAV to takeoff safely under wide range wind disturbances (e.g., downburst, wind turbulence) with the help of ADRC.

Line-feature-based calibration method of structured light plane parameters for robot hand-eye system

Abstract. For monocular-structured light vision measurement, it is essential to calibrate the structured light plane parameters in addition to the camera intrinsic parameters. A line-feature-based calibration method of structured light plane parameters for a robot hand-eye system is proposed. Structured light stripes are selected as calibrating primitive elements, and the robot moves from one calibrating position to another with constraint in order that two misaligned stripe lines are generated. The images of stripe lines could then be captured by the camera fixed at the robot’s end link. During calibration, the equations of two stripe lines in the camera coordinate system are calculated, and then the structured light plane could be determined. As the robot’s motion may affect the effectiveness of calibration, so the robot’s motion constraints are analyzed. A calibration experiment and two vision measurement experiments are implemented, and the results reveal that the calibration accuracy can meet the precision requirement of robot thick plate welding. Finally, analysis and discussion are provided to illustrate that the method has a high efficiency fit for industrial in-situ calibration.

Autolanding of unmanned aerial vehicles based on Active Disturbance Rejection Control

The safe landing of unmanned aerial vehicles (UAVs) under various wind conditions has been a challenging task for decades. We design an autolanding control system which consists of a throttle control subsystem and an altitude control subsystem based on the Active Disturbance Rejection Control (ADRC). In contrast to previous methods, our approach can directly and real-timely estimate the UAVs internal and external disturbances and then compensate for them. Simulation results show that our autolanding control system can land the UAV safely under wide range wind disturbances (e.g., wind turbulence, wind shear) with the help of ADRC.

Residual vibration suppression using off-line learning input shaping method for a flexible joint robot

This paper presents a two-impulse input shaping method using off-line learning method to suppress the residual vibration of a flexible joint robot which is considered as perform repetitive tasks. It has been proved that the two-impulse input shaping method has the ability to suppress time-varying or nonlinear residual vibration. However, the parameters of the input shaper are difficult to select. In this paper, a method based on the off-line learning is presented to determine the proper parameters. We found that the torque of the joint can reflect the residual vibration through analysis of relations between the residual vibration and torque of the flexible joint robot. Thus, the torque signal of the joint is used to measure the vibration magnitude and no additional sensors for vibration measurement are required. For the nonmeasurable of the phase of the residual vibration, only the vibration magnitude is used to update the parameters of the input shaper off-line until the minimum vibration is obtained. The initial parameters of the input shaper also are estimated in this paper. Simulations are conducted to suppress residual vibration of a flexible joint robot, thereby demonstrating the effectiveness of the off-learning learning input shaping method.

Modeling, control and software implementation of astronomical tracking of focus cabin suspension of FAST

This article describes the control algorithm and software implementation of astronomical tracking based on the mechanical analysis for Five-hundred-meter Aperture Spherical Telescope(FAST) that is being built in Guizhou province of China, which aims to help astronomers resolve questions in cosmology. On the basis of position and attitude feedback algorithm of cable driven parallel robot, the control of X-Y positioner with feed-forward was introduced and the astronomical tracking experiments were conducted on scale model to verify the validity of control strategy. The future works for focus cabin suspension of FAST are also pointed out.

Experimental validation of a trajectory planning method with continuous acceleration implemented on a DSP-based motion controller

A trajectory planning method in joint space which provides a continuity of position, velocity and acceleration just with simple numerical simulations was already presented by us before. This paper, therefore, presents techniques in detail for implementation of it. To guarantee high performance, a novel DSP-based multiaxis motion controller is developed for executing the trajectory planning method on-line. Hardware design and software design of the motion controller is described. Finally, the proposed trajectory planning method is tested based on the proposed motion controller for an arc welding robot. Experimental results and performances evaluation are also presented in this paper.

Unsupervised learning of categories from sets of partially matching image features for power line inspection robot

Object recognition and categorization are considered as fundamental steps in the vision based navigation for inspection robot as it must plan its behaviors based on various kinds of obstacles detected from the complex background. However, current approaches typically require some amount of supervision, which is viewed as a expensive burden and restricted to relatively small number of applications in practice. For this purpose, we present an computationally efficient approach that does not need supervision and is capable of learning object categories automatically from unlabeled images which are represented by an set of local features, and all sets are clustered according to their partial-match feature correspondences, which is done by a enhanced Spatial Pyramid Match algorithm (E-SPK). Then a graph-theoretic clustering method is applied to seek the primary grouping among the images. The consistent subsets within the groups are identified by inferring category templates. Given the input, the output of the approach is a partition of the images into a set of learned categories. We demonstrate this approach on a field experiment for a powerline inspection robot.

Research on astronomical trajectory planning algorithm for FAST

This paper addresses astronomical trajectory planning algorithms for tracking and basket-weaving for Five-hundred-meter Aperture Spherical Radio Telescope (FAST). In order to achieve stable operation at feed receiver of FAST and to ease difficulties of trajectory planning in 3-D space, the observed trajectories were planned in celestial coordinate system. Firstly, the characteristics of tracking and basket-weaving were analyzed, and the involved parameters for tracking and basket-weaving were extracted. Secondly, the constraint conditions for planning parameters corresponding to the practical motion were obtained; besides trajectory planning algorithms based on double S velocity profile for tracking and basket-weaving were proposed. Finally, the numerical results indicated that the planned trajectories are guaranteed to be continuous in position, velocity and acceleration, as well as respect the given motion constraint conditions. And the proposed algorithm cost less planning time than the algorithm plans in 3-D space.