Proficiency of statistical moment-based methods for analysis of positional accuracy reliability of industrial robots

Abstract Industrial robots are increasingly used in machining tasks because of their high flexibility and intelligence. However, the low structural stiffness of the robot seriously affects the positional accuracy and machining quality of robot operation equipment. Studying robot stiffness characteristics and optimization methods is an effective way to improve robot stiffness performance. Accordingly, aiming at the poor accuracy of stiffness modeling caused by approximating stiffness of each joint as constant, a variable stiffness identification method is proposed based on space gridding. Then, a task-oriented axial stiffness evaluation index is proposed to realize quantitative assessment of the stiffness performance in the machining direction. Besides, by analyzing the redundant kinematic characteristics of the robot machining system, a configuration optimization method is further come up with to maximize the index. For a large number of points or trajectory processing tasks, a configuration smoothing strategy is proposed to achieve fast acquisition of optimized configurations. Finally, experiments on a KR500 robot are conducted to verify the feasibility and validity of proposed stiffness identification and configuration optimization methods.

Download Full-text

Deflection model for robotic friction stir welding

Industrial Robot the international journal of robotics research and application ◽

10.1108/ir-01-2014-0301 ◽

2014 ◽

Vol 41 (4) ◽

pp. 365-372 ◽

Cited By ~ 12

Author(s):

Jeroen De Backer ◽

Gunnar Bolmsjö

Keyword(s):

Friction Stir Welding ◽

Force Feedback ◽

Force Sensor ◽

Industrial Robots ◽

Positional Accuracy ◽

Content Type ◽

Friction Stir ◽

Robot Controller ◽

External Forces ◽

Robotic Friction Stir Welding

Purpose – This paper aims to present a deflection model to improve positional accuracy of industrial robots. Earlier studies have demonstrated the lack of accuracy of heavy-duty robots when exposed to high external forces. One application where the robot is pushed to its limits in terms of forces is friction stir welding (FSW). This process requires the robot to deliver forces of several kilonewtons causing deflections in the robot joints. Especially for robots with serial kinematics, these deflections will result in significant tool deviations, leading to inferior weld quality. Design/methodology/approach – This paper presents a kinematic deflection model, assuming a rigid link and flexible joint serial kinematics robot. As robotic FSW is a process which involves high external loads and a constant welding speed of usually below 50 mm/s, many of the dynamic effects are negligible. The model uses force feedback from a force sensor, embedded on the robot, and predicts the tool deviation, based on the measured external forces. The deviation is fed back to the robot controller and used for online path compensation. Findings – The model is verified by subjecting an FSW tool to an external load and moving it along a path, with and without deviation compensation. The measured tool deviation with compensation was within the allowable tolerance for FSW. Practical implications – The model can be applied to other robots with a force sensor. Originality/value – The presented deflection model is based on force feedback and can predict and compensate tool deviations online.

Download Full-text

Active Vibration Control for Robotic Machining

Volume 2: Advanced Manufacturing ◽

10.1115/imece2017-71670 ◽

2017 ◽

Cited By ~ 3

Author(s):

Zheng Wang ◽

Patrick Keogh

Keyword(s):

Vibration Control ◽

Low Cost ◽

Active Vibration Control ◽

Experimental Studies ◽

Industrial Robots ◽

Positional Accuracy ◽

Robotic Machining ◽

Working Volume ◽

Robot Machining ◽

Active Vibration

Due to their flexibility, low cost and large working volume, 6-axis articulated industrial robots are being used increasingly for drilling, trimming and machining operations. However, producing high quality components has proven to be difficult, as a result of the inherent problems of robots, including low structural stiffness, hence excitation of structural modes, low positional accuracy, and bandwidth limitations associated with dynamics and control. These limit robotic machining to non-critical components and parts with low accuracy and surface finish requirements. As a part of the “Light Controlled Factory” project at the University of Bath, studies have been carried out to improve robotic machine capability, specifically positioning accuracy and vibration reduction. This paper describes experimental studies in reducing robot machining vibrations induced by cutting forces with active vibration control, using accelerometers to measure vibration and inertial actuators to mitigate vibration forces. With a relatively simple controller, a 25% reduction of RMS vibration amplitude is demonstrated.

Download Full-text

Real-Time Laser Tracker Compensation of Robotic Drilling and Machining

Journal of Manufacturing and Materials Processing ◽

10.3390/jmmp4030079 ◽

2020 ◽

Vol 4 (3) ◽

pp. 79 ◽

Cited By ~ 1

Author(s):

Zheng Wang ◽

Runan Zhang ◽

Patrick Keogh

Keyword(s):

Real Time ◽

Degrees Of Freedom ◽

Low Cost ◽

Industrial Robots ◽

Laser Tracker ◽

Positional Accuracy ◽

Working Volume ◽

Machining Test ◽

Critical Components ◽

Aluminum Part

Due to their flexibility, low cost and large working volume, 6-axis articulated industrial robots are increasingly being used for drilling, trimming and machining operations, especially in aerospace manufacturing. However, producing high quality components has demonstrated to be difficult, as a result of the inherent problems of robots, including low structural stiffness and low positional accuracy. These limit robotic machining to non-critical components and parts with low accuracy and surface finish requirements. Studies have been carried out to improve robotic machine capability, specifically positioning accuracy and vibration reduction. This study includes the description of the hardware, software and methodologies developed to compensate robot path errors in real time using a single three-degrees-of-freedom (DOF) laser tracker, as well as the experimental results with and without compensation. Performance tests conducted include ballbar dynamic path accuracy test, a series of drilling case studies and a machining test. The results demonstrate major improvements in path accuracy, hole position accuracy and hole quality, as well as increases in accuracy of a machined aluminum part.

Download Full-text

Hyperparameter Optimization of Artificial Neural Networks to Improve the Positional Accuracy of Industrial Robots

Journal of Machine Engineering ◽

10.36897/jme/134275 ◽

2021 ◽

pp. 47-59

Author(s):

Eckart Uhlmann ◽

Mitchel Polte ◽

Julian Blumberg ◽

Zhoulong Li ◽

Adrian Kraft

Keyword(s):

Neural Networks ◽

Artificial Neural Networks ◽

Industrial Robots ◽

Positional Accuracy ◽

Hyperparameter Optimization ◽

Artificial Neural

Download Full-text

Calibration and Compensation of Rotary Axis Angular Positioning Deviations on a SCARA-Type Industrial Robot Using a Laser Tracker

JSME 2020 Conference on Leading Edge Manufacturing/Materials and Processing ◽

10.1115/lemp2020-8502 ◽

2020 ◽

Author(s):

Nan Zhao ◽

Soichi Ibaraki

Keyword(s):

Rotation Axis ◽

Industrial Robot ◽

Kinematic Model ◽

Industrial Robots ◽

Laser Tracker ◽

Link Length ◽

Positional Accuracy ◽

Positioning Accuracy ◽

Rotary Axis ◽

The Absolute

Abstract In general, the “absolute” positioning accuracy of industrial robots is significantly lower than its repeatability. In the past research, in order to improve a robot’s positioning accuracy over the entire workspace, the compensation for the link length errors and the rotation axis angle offsets are often employed. However, the positioning error of the compensated industrial robot is still much higher than that of a typical machine tool. The purpose of this study is to propose a new kinematic model and its calibration scheme to further improve the absolute positional accuracy of an industrial robot over the entire workspace. In order to simplify the problem, this study only targets the 2D positioning accuracy of a SCARA-type robot. The proposed model includes not only link length errors and rotary axis angular offsets but also the “error map” of the angular positioning deviation of each rotary axis. The angular error deviation of each rotary axis is identified by measuring the robot’s end-effector position by a laser tracker at many positions. To verify the validity of the identified model, the effectiveness of the compensation based on it is also investigated.

Download Full-text

A new elastic structure for a compliant robot wrist

Robotica ◽

10.1017/s0263574700001235 ◽

1983 ◽

Vol 1 (2) ◽

pp. 95-102 ◽

Cited By ~ 12

Author(s):

Štefan Havlík

Keyword(s):

Geometrical Parameter ◽

Cost Effective ◽

Industrial Robots ◽

Elastic Structure ◽

Positional Accuracy ◽

Robot Wrist ◽

Compliant Robot ◽

Parameter Synthesis ◽

Automatic Matching ◽

Intended Use

SUMMARYA new elastic structure of a robot wrist, which exhibits a six decree of freedom flexural capability, is described. Force and compliance analysis is made, and algorithms for geometrical parameter synthesis are proposed. Owing to the technological simplicity of the designed structure, it is possible to construct cost-effective compliance devices. The intended use is to permit the assembly of close tolerance parts with industrial robots having relatively low positional accuracy. It could also be applied to other manual or automatic matching operations.

Download Full-text

SAFETY AND RISK ASSESSMENT AT AUTOMATED WORKPLACE

TECHNICAL SCIENCES AND TECHNOLOG IES ◽

10.25140/2411-5363-2018-4(14)-78-84 ◽

2018 ◽

pp. 78-84

Author(s):

Marek Vagas

Keyword(s):

Risk Assessment ◽

Industrial Robot ◽

Industrial Robots ◽

Added Value ◽

Growing Up ◽

Target Setting ◽

Clear View ◽

General Safety

Urgency of the research. Automated workplaces are growing up in present, especially with implementation of industrial robots with feasibility of various dispositions, where safety and risk assessment is considered as most important issues. Target setting. The protection of workers must be at the first place, therefore safety and risk assessment at automated workplaces is most important problematic, which had presented in this article Actual scientific researches and issues analysis. Actual research is much more focused at standard workplaces without industrial robots. So, missing of information from the field of automated workplaces in connection with various dispositions can be considered as added value of article. Uninvestigated parts of general matters defining. Despite to lot of general safety instructions in this area, still is missed clear view only at automated workplace with industrial robots. The research objective. The aim of article is to provide general instructions directly from the field of automated workplaces The statement of basic materials. For success realization of automated workplace is good to have a helping hand and orientation requirements needed for risk assessment at the workplace. Conclusions. The results published in this article increase the awareness and information of such automated workplaces, together with industrial robots. In addition, presented general steps and requirements helps persons for better realization of these types of workplaces, where major role takes an industrial robot. Our proposed solution can be considered as relevant base for risk assessment such workplaces with safety fences or light barriers.

Download Full-text