Xiao-Wei Tu

Switching Control of Image-Based Visual Servoing With Laser Pointer in Robotic Manufacturing Systems

In this paper, an Eye-in-Hand robotic system with laser pointer is developed to detect, grasp, and assemble a planar object on a main body in robotic manufacturing systems. This paper is focused on detecting the object and moving the end effector to a position where a pump can perfectly suck up the object. A switching control of image-based visual servoing (IBVS) is designed to control the pose of the end effector with respect to the stationary object so that the image features of the planar object observed by the camera converge to the target image features for the further assembly. A simple off-the-shelf laser pointer is adopted to realize the depth estimation for obtaining the image Jacobian matrices. By using a laser spot as an image feature and the separate degree-of-freedom method, the proposed switch-control algorithm decouples the rotational and translational motions of the camera to avoid the inherent drawbacks of traditional IBVS. The experiments on a robotic assembly system are given to verify the effectiveness of the proposed method.

Performance-based parameter tuning method of model-driven PID control systems

In this paper, performance-based parameter tuning method of model-driven Two-Degree-of-Freedom PID (MD TDOF PID) control system has been proposed to enhance the control performances of a process. Known for its ability of stabilizing the unstable processes, fast tracking to the change of set points and rejecting disturbance, the MD TDOF PID has gained research interest recently. The tuning methods for the reported MD TDOF PID are based on internal model control (IMC) method instead of optimizing the performance indices. In this paper, an Integral of Time Absolute Error (ITAE) zero-position-error optimal tuning and noise effect minimizing method is proposed for tuning two parameters in MD TDOF PID control system to achieve the desired regulating and disturbance rejection performance. The comparison with Two-Degree-of-Freedom control scheme by modified smith predictor (TDOF CS MSP) and the designed MD TDOF PID tuned by the IMC tuning method demonstrates the effectiveness of the proposed tuning method.

Switching control of image based visual servoing with laser pointer in robotic assembly systems

In this paper, a switching control of Image Based Visual Servoing (IBVS) with laser pointer is introduced to control the pose of the end effector with respect to the stationary object in a robotic assembly system so that the image features observed by the camera reach the desired image features as fast as possible. The simple off-the-shelf laser pointer is adopted to realize the depth estimation for obtaining the image Jacobian matrices. By using a laser spot as an image feature and the partition Degree-Of-Freedom (DOF) method, the proposed switching control algorithm decouples the rotational and translational motion control of the robotic end effector to avoid the inherent drawbacks of traditional IBVS, such as image singularities, image local minima and relative long trajectory in Cartesian space. The experimental results on a robotic assembly system are given to verify the effectiveness of the proposed method.

Multiple cameras-multiple target points visual servoing in large scale 3D manufacturing systems

This article addresses the multiple cameras — multiple target points visual servoing system to correct the pose of robot end-effector in large scale manufacturing systems. The end-effector of a 6 Degree-of-Freedom (DOF) robot holds the workpiece and four cameras are used as visual sensors and installed on the workpiece to capture the image features of target points. Four pairs of light emitted diodes (LEDs) are installed above the workpiece configured in a way that, each pair LED can be observed by only one camera. One pair LED contains one target point for visual servoing and one complimentary point for estimating the depth of the corresponding target point to relevant camera. In this configuration, the depth of each target point to the corresponding camera is readily obtained by using the stereo vision method. Hence, the image Jacobian matrices can be precisely calculated during visual servoing. An imaged based visual servoing (IBVS) controller is designed to control the pose of the end-effector of robot and hence that of the work piece. By observing the four target points, the IBVS can drive the workpiece to the desired position in robot base frame. Extensive simulation has been carried out to verify the effectiveness of the proposed method.

Improved parameters tuning method of model-driven PID control systems

In this paper, an improved parameters tuning method of model-driven two degree of freedom PID control system has been proposed to enhance the control performances of a PID controlled system. Known for its ability of stabilizing the unstable processes, fast tracking to the change of set points and rejecting disturbance, the model-driven two degree of freedom PID — so called MD TDOF PID has gained research interest recently. The tuning methods for the previous MD TDOF PID are based on internal model control (IMC) method. In this paper, an integral of time and absolute error (ITAE) tuning and noise effect minimizing method is proposed for two parameters in MD TDOF PID control system to achieve the desired regulating and disturbance rejection performance. The comparison with traditional PID controller and the designed MD TDOF PID in [6] demonstrate the effectiveness of the proposed tuning methods.

A data decorrelation method for 3D position measurements from a line sensors based photogrammetric measuring system

In this study, a data decorrelation method is developed for processing 3D position measurements obtained by a line sensors based photogrammetric measuring system. The measured 3D data suffer from correlations due to the principle of the triangulation. This nature causes complexity when a calibration procedure is carried out. Additionally, the correlated data may affect its further exploration and applications, such as robot visual servoing. For this reason, a data decorrelation method based on multivariate statistical analysis is proposed to preprocess the 3D coordinate measurements, in such a way that each component of the coordinate can be treated individually. Consequently, the calibration procedure can be significantly simplified in a less time and memory consuming manner. The proposed method includes the local and global data decorrelation. Evaluation and comparisons of these two approaches have been analyzed with a conclusion on the better performance of the global data decorrelation. The optimal decorrelated configuration based on the results has been identified for the measuring system.