The industrial robot reducer testing instrument dynamic torsional moment measurement error calibration, based on the Bisquare curve fitting-improved Bayes particle swarm optimization-nonlinear echo state network (BCF-IBPSO-NESN) method

Industrial robots are important components in the production and manufacturing industry. As a core component of the industrial robot, the industrial robot reducer plays a crucial role in the performance of the entire industrial robot. The error analysis and accuracy traceability of the industrial robot reducer testing instrument are of great significance in improving the quality of the precision reducer. Therefore, it is essential to calibrate the dynamic torsional moment measurement error of the instrument. The features of the dynamic torsional moment measurement error are analyzed in this paper. Based on these features, a new dynamic torsional moment measurement error calibration method is proposed based on the Bisquare curve fitting-improved Bayes particle swarm optimization-nonlinear echo state network (BCF-IBPSO-NESN) algorithm. The proposed method focuses on calibrating the dynamic torsional moment measurement error of the industrial robot reducers in real time. The experimental results show that the dynamic torsional moment measurement error of the input side torsional moment measurement module and the output side torsional moment measurement module can be reduced to ±0.05 Nm and ±1 Nm, respectively. The contribution of this paper is that the method calibrates the dynamic torsional moment measurement error. It supplies a guideline for calibrating the dynamic torsional moment measurement error of the instrument under any load.

A Calibration Method for a Laser Triangulation Scanner Mounted on a Robot Arm for Surface Mapping

This paper presents and discusses a method to calibrate a specially built laser triangulation sensor to scan and map the surface of hydraulic turbine blades and to assign 3D coordinates to a dedicated robot to repair, by welding in layers, the damage on blades eroded by cavitation pitting and/or cracks produced by cyclic loading. Due to the large nonlinearities present in a camera and laser diodes, large range distances become difficult to measure with high precision. Aiming to improve the precision and accuracy of the range measurement sensor based on laser triangulation, a calibration model is proposed that involves the parameters of the camera, lens, laser positions, and sensor position on the robot arm related to the robot base to find the best accuracy in the distance range of the application. The developed sensor is composed of a CMOS camera and two laser diodes that project light lines onto the blade surface and needs image processing to find the 3D coordinates. The distances vary from 250 to 650 mm and the accuracy obtained within the distance range is below 1 mm. The calibration process needs a previous camera calibration and special calibration boards to calculate the correct distance between the laser diodes and the camera. The sensor position fixed on the robot arm is found by moving the robot to selected positions. The experimental procedures show the success of the calibration scheme.

Visual Servoing of Robot Manipulators Part I: Projective Kinematics

Visual servoing of robot manipulators is a key technique where the appearance of an object in the image plane is used to control the velocity of the end-effector such that the desired position is reached in the scene. The vast majority of visual servoing methods proposed so far uses calibrated robots in conjunction with calibrated cameras. It has been shown that the behavior of visual control loops does not degrade too much in the presence of calibration errors. Nevertheless, camera and robot calibration are complex and time-consuming processes requiring special-purpose mechanical devices, such as theodolites and calibration jigs.

In this paper, we suggest formulating a visual servoing control loop in a nonmetric space, which in our case amounts to the projective space in which a triangulation of the scene using an uncalibrated stereo rig is expressed. The major consequence of controlling the robot in nonmetric space rather than in Euclidean space is that both the robot’s direct kinematic map and the robot’s Jacobian matrix must be defined in this space as well.

The elementary joint-space motions that can be performed by a robot manipulator are pure rotations and pure translations. Traditionally, these motions are represented as Euclidean transformations. Since these motions are observed with an uncalibrated stereo rig, it will be convenient to represent them as projective transformations (homographies) rather than Euclidean transformations. Indeed, it will be shown that rotations and translations can be parameterized as special cases of homographies, which will be called projective rotations and projective translations. The algebraic properties of this nonmetric representation of elementary motions will be thoroughly investigated allowing us to characterize the direct kinematic map and the Jacobian matrix of a manipulator. Therefore, we introduce the concepts of projective kinematics and a projective Jacobian matrix. Unlike the classical robot Jacobian matrix of a manipulator that relates the robot joint-velocities to the kinematic screw associated with the end-effector, we establish a direct relationship between joint-velocities and image-plane velocities. The latter are velocities associated with image points arising from the 3-D to 2-D projection of end-effector points.

Finally, we provide a practical method to estimate the projec tive kinematic model and we describe some preliminary simulated experiments that use this nonmetric model to perform stereo-based servoing. Nevertheless, in-depth analysis of projective control will be the topic of a forthcoming paper.

Survey of Research for Performance Measurement of Mobile Manipulators

This survey provides the basis for developing research in the area of mobile manipulator performance measurement, an area that has relatively few research articles when compared to other mobile manipulator research areas. The survey provides a literature review of mobile manipulator research with examples of experimental applications. The survey also provides an extensive list of planning and control references as this has been the major research focus for mobile manipulators which factors into performance measurement of the system. The survey then reviews performance metrics considered for mobile robots, robot arms, and mobile manipulators and the systems that measure their performance, including machine tool measurement systems through dynamic motion tracking systems. Lastly, the survey includes a section on research that has occurred for performance measurement of robots, mobile robots, and mobile manipulators beginning with calibration, standards, and mobile manipulator artifacts that are being considered for evaluation of mobile manipulator performance.

Kinematic Calibration of Parallel Robots for Docking Mechanism Motion Simulation

A new method for calibrating a parallel robot is proposed as part of a project aimed at developing a calibration method for spacecraft docking mechanism motion simulator. To implement this method, a calibration equation is built by generating the constraint conditions of the end-effector's motion in the workspace using a three-dimensional coordinate measuring machine. According to the established calibration equation and the simulation, the geometrical parameters of the parallel robot are identified. The effectiveness of the calibration method with a coordinate measuring machine is verified through random pose test experiment.

Laser-scan endoscope system for intraoperative geometry acquisition and surgical robot safety management

In laparoscopic surgery, surgeons find particular difficulties related to the operation technique. Due to restricted view, lack of depth information from the monocular endoscope and limited degree of freedom, surgeons find their movements impeded. A support system that provides improved laparoscopic vision would help to overcome the difficulties. If real-time visualization of abdominal structures were feasible, more accurate procedures and improved quantitative evaluations in laparoscopic surgery might be possible. In this study, a laser-scan endoscope system was developed to acquire and visualize the shape and texture of the area of interest instantaneously. The intraoperative geometric information of deformable organ could be applied for robotic safety management via geometric computation of robot position and organ shape. Results of in vivo experiments on a pig liver verified effectiveness of the proposed system.