scholarly journals An Analysis of Joint Assembly Geometric Errors Affecting End-Effector for Six-Axis Robots

Robotics ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 27
Author(s):  
Chana Raksiri ◽  
Krittiya Pa-im ◽  
Supasit Rodkwan
Keyword(s):  
Industrial Robot ◽  
Kinematic Model ◽  
Measurement Data ◽  
Geometric Error ◽  
Laser Tracker ◽  
Geometric Errors ◽  
Actual Measurement ◽  
End Effector ◽  
Position Errors ◽  
Joint Assembly

This paper presents an analysis of the geometric errors of joint assembly that affect the end-effector for a six-axis industrial robot. The errors were composed of 30 parameters that come from the Geometric Dimensioning and Tolerancing (GD&T) design, which is not the normal way to describe them. Three types of manufacturing tolerancing—perpendicularity, parallelism and position—were introduced and investigated. These errors were measured by the laser tracker. The measurement data were calculated with an analysis of the circle fitting method. The kinematic model and error model based on a combination of translations methods were used. The experiment was carried out in order to calculate the tolerancing of geometric error. Then, the positions of the end-effector in the actual measurement from laser tracker and exact performance were compared. The discrepancy was compensated by offline programming. As a result, the position errors were reduced by 90%.

A Strategy for Geometric Error Characterization in Multi-Axis Machine Tool by Use of a Laser Tracker

2014 ◽  
Vol 615 ◽  
pp. 22-31 ◽  
Author(s):  
Sergio Aguado ◽  
Jorge Santolaria ◽  
David Samper ◽  
Juan Jose Aguilar Martín
Keyword(s):  
Machine Tool ◽  
Kinematic Model ◽  
Kinematic Chain ◽  
Geometric Error ◽  
Laser Tracker ◽  
Geometric Errors ◽  
Kinematic Chains ◽  
Error Characterization ◽  
Machine Tool Accuracy ◽  
The Relationship

This paper aims to present different methods of volumetric verification in long range machine toll with lineal and rotary axes using a commercial laser tracker as measurement system. This method allows characterizing machine tool geometric errors depending on the kinematic of the machine and the work space available during the measurement time. The kinematic of the machine toll is affected by their geometric errors, which are different depending on the number and type of movement axes. The relationship between the various geometrical errors is different from relationship obtained in machine tool whit only lineal axes. Therefore, the identification strategy should be different. In the same way, the kinematic chain of the machine tool determines determines the position of the laser tracker and available space for data capture. This paper presents the kinematic model of several machine tools with different kinematic chains use to improve the machine tool accuracy of each one by volumetric verification. Likewise, the paper thus presents a study of: the adequacy of different nonlinear optimization strategies depending on the type of axis and the usable space available.

scholarly journals New Method and Portable Measurement Device for the Calibration of Industrial Robots

Sensors ◽  
2020 ◽  
Vol 20 (20) ◽  
pp. 5919
Author(s):  
Caglar Icli ◽  
Oleksandr Stepanenko ◽  
Ilian Bonev
Keyword(s):  
Industrial Robot ◽  
Calibration Method ◽  
Industrial Robots ◽  
Laser Tracker ◽  
Calibration Model ◽  
Measuring Device ◽  
End Effector ◽  
New Device ◽  
Position Errors ◽  
Measuring Machine

This paper presents an automated calibration method for industrial robots, based on the use of (1) a novel, low-cost, wireless, 3D measuring device mounted on the robot end-effector and (2) a portable 3D ball artifact fixed with respect to the robot base. The new device, called TriCal, is essentially a fixture holding three digital indicators (plunger style), the axes of which are orthogonal and intersect at one point, considered to be the robot tool center point (TCP). The artifact contains four 1-inch datum balls, each mounted on a stem, with precisely known relative positions measured on a Coordinate Measuring Machine (CMM). The measurement procedure with the TriCal is fully automated and consists of the robot moving its end-effector in such as a way as to perfectly align its TCP with the center of each of the four datum balls, with multiple end-effector orientations. The calibration method and hardware were tested on a six-axis industrial robot (KUKA KR6 R700 sixx). The calibration model included all kinematic and joint stiffness parameters, which were identified using the least-squares method. The efficiency of the new calibration system was validated by measuring the accuracy of the robot after calibration in 500 nearly random end-effector poses using a laser tracker. The same validation was performed after the robot was calibrated using measurements from the laser tracker only. Results show that both measurement methods lead to similar accuracy improvements, with the TriCal yielding maximum position errors of 0.624 mm and mean position errors of 0.326 mm.

Industrial Robot Error Compensation Using Laser Tracker System

2008 ◽  
Vol 381-382 ◽  
pp. 579-582
Author(s):  
Jian Fei Ouyang ◽  
W. Liu ◽  
Xing Hua Qu ◽  
Y. Yan
Keyword(s):  
Real Time ◽  
Error Compensation ◽  
Industrial Robot ◽  
Laser Tracker ◽  
Geometric Errors ◽  
End Effector ◽  
Geometry Error

A technique to compensate the geometry errors of industrial robot using Laser Tracker System (LTS) has been presented in this paper. A Spherically Mounted Retro-reflector (SMR) is mounted on the end-effector of industrial robot. The positions of SMR are measured by LTS and compared with the nominal value of industrial robot to get geometry error database of robot. The updated error database, together with real-time measuring of the positions on the robot’s end-effector can be used to compensate the geometric errors of the robot. Using this technique to compensate the industrial robot, the geometry errors can be decreased from 0.1mm to 0.04mm.

Table-Based Volumetric Error Compensation of Large Five-Axis Machine Tools

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Jennifer Creamer ◽  
Patrick M. Sammons ◽  
Douglas A. Bristow ◽  
Robert G. Landers ◽  
Philip L. Freeman ◽  
...  
Keyword(s):  
Machine Tool ◽  
Error Compensation ◽  
Machine Tools ◽  
Data Gathering ◽  
Measurement Data ◽  
Geometric Error ◽  
Compensation Method ◽  
Geometric Errors ◽  
Simultaneous Generation ◽  
Five Axis

This paper presents a geometric error compensation method for large five-axis machine tools. Compared to smaller machine tools, the longer axis travels and bigger structures of a large machine tool make them more susceptible to complicated, position-dependent geometric errors. The compensation method presented in this paper uses tool tip measurements recorded throughout the axis space to construct an explicit model of a machine tool's geometric errors from which a corresponding set of compensation tables are constructed. The measurements are taken using a laser tracker, permitting rapid error data gathering at most locations in the axis space. Two position-dependent geometric error models are considered in this paper. The first model utilizes a six degree-of-freedom kinematic error description at each axis. The second model is motivated by the structure of table compensation solutions and describes geometric errors as small perturbations to the axis commands. The parameters of both models are identified from the measurement data using a maximum likelihood estimator. Compensation tables are generated by projecting the error model onto the compensation space created by the compensation tables available in the machine tool controller. The first model provides a more intuitive accounting of simple geometric errors than the second; however, it also increases the complexity of projecting the errors onto compensation tables. Experimental results on a commercial five-axis machine tool are presented and analyzed. Despite significant differences in the machine tool error descriptions, both methods produce similar results, within the repeatability of the machine tool. Reasons for this result are discussed. Analysis of the models and compensation tables reveals significant complicated, and unexpected kinematic behavior in the experimental machine tool. A particular strength of the proposed methodology is the simultaneous generation of a complete set of compensation tables that accurately captures complicated kinematic errors independent of whether they arise from expected and unexpected sources.

Comparison of two calibration methods for a small industrial robot based on an optical CMM and a laser tracker

Robotica ◽  
2013 ◽  
Vol 32 (3) ◽  
pp. 447-466 ◽  
Author(s):  
Albert Nubiola ◽  
Mohamed Slamani ◽  
Ahmed Joubair ◽  
Ilian A. Bonev
Keyword(s):  
Industrial Robot ◽  
Laser Tracker ◽  
Calibration Model ◽  
Kinematic Calibration ◽  
Absolute Accuracy ◽  
Parameter Calibration ◽  
End Effector ◽  
Coordinate Measurement ◽  
Measurement Systems ◽  
Calibration Methods

SUMMARYThe absolute accuracy of a small industrial robot is improved using a 30-parameter calibration model. The error model takes into account a full kinematic calibration and five compliance parameters related to the stiffness in joints 2, 3, 4, 5, and 6. The linearization of the Jacobian is performed to iteratively find the modeled error parameters. Two coordinate measurement systems are used independently: a laser tracker and an optical CMM. An optimized end-effector is developed specifically for each measurement system. The robot is calibrated using fewer than 50 configurations and the calibration efficiency validated in 1000 configurations using either the laser tracker or the optical CMM. A telescopic ballbar is also used for validation. The results show that the optical CMM yields slightly better results, even when used with the simple triangular plate end-effector that was developed mainly for the laser tracker.

Calibration of geometric and non-geometric errors of an industrial robot

Robotica ◽  
2001 ◽  
Vol 19 (3) ◽  
pp. 311-321 ◽  
Author(s):  
Joon Hyun Jang ◽  
Soo Hyun Kim ◽  
Yoon Keun Kwak
Keyword(s):  
Industrial Robot ◽  
Radial Basis Function Network ◽  
Three Dimensional ◽  
Geometric Errors ◽  
Position Measurement ◽  
End Effector ◽  
Calibration Equation ◽  
New Approach ◽  
Joint Deformation ◽  
Six Dof

Inaccurate positioning of the robot end effector causes joint deformation as well as geometric errors when an industrial robot has a payload at its end effector. We propose a new approach of calibration which deals with joint angle dependent errors to compensate for these phenomena. To implement this method, we divided the robot workspace into several local regions, and built a calibration equation by generating the constraint conditions of the end effector's motion in each local region using a three-dimensional position measurement system. The parameter errors obtained this way were interpolated using the Radial Basis Function Network (RBFN) so as to estimate calibration errors in the regions that we did not measure. We used this technique to improve the performance of a six DOF industrial robot used for arc welding.

Geometric Error Compensation With a Six Degree-of–Freedom Rotary Magnetic Actuator

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Alexander Yuen ◽  
Yusuf Altintas
Keyword(s):  
Real Time ◽  
Kinematic Model ◽  
Geometric Error ◽  
Degree Of Freedom ◽  
Geometric Errors ◽  
Working Volume ◽  
Quintic Polynomial ◽  
Gradient Descent Algorithm ◽  
Forward Kinematic ◽  
Six Degree Of Freedom

This paper presents a methodology to compensate the tooltip position errors caused by the geometric errors of a three-axis gantry type micromill integrated with a six degree-of-freedom (6DOF) rotary magnetic table. A geometric error-free ideal forward kinematic model of the nine-axis machine has been developed using homogenous transformation matrices (HTMs). The geometric errors of each linear axis, which include one positioning, two straightness, pitch, roll, and yaw errors, are measured with a laser interferometer and fit to quintic polynomial functions in the working volume of the machine. The forward kinematic model is modified to include the geometric errors which, when subtracted from the ideal kinematic model, gives the deviation between the desired tooltip position with and without geometric errors. The position commands of the six degree-of-freedom rotary magnetic table are modified in real time to compensate for the tooltip deviation using a gradient descent algorithm. The algorithm is simulated and verified experimentally on the nine-axis micromill controlled by an in-house developed virtual/real-time open computer numerical controlled (CNC) system.

scholarly journals A Methodology for Industrial Robot Calibration Based on Measurement Sub-Regions

2021 ◽  
Author(s):  
Juan Sebastian Toquica ◽  
José Maurı́cio Motta
Keyword(s):  
Industrial Robot ◽  
Low Cost ◽  
Kinematic Model ◽  
Measurement Data ◽  
Industrial Applications ◽  
Industrial Robots ◽  
Robot Calibration ◽  
High Precision Measurement ◽  
Measurement Systems ◽  
Robot Accuracy

Abstract This paper proposes a methodology for calibration of industrial robots that uses a concept of measurement sub-regions, allowing low-cost solutions and easy implementation to meet the robot accuracy requirements in industrial applications. The solutions to increasing the accuracy of robots today have high-cost implementation, making calibration throughout the workplace in industry a difficult and unlikely task. Thus, reducing the time spent and the measured workspace volume of the robot end-effector are the main benefits of the implementation of the sub-region concept, ensuring sufficient flexibility in the measurement step of robot calibration procedures. The main contribution of this article is the proposal and discussion of a methodology to calibrate robots using several small measurement sub-regions and gathering the measurement data in a way equivalent to the measurements made in large volume regions, making feasible the use of high-precision measurement systems but limited to small volumes, such as vision-based measurement systems. The robot calibration procedures were simulated according to the literature, such that results from simulation are free from errors due to experimental setups as to isolate the benefits of the measurement proposal methodology. In addition, a method to validate the analytical off-line kinematic model of industrial robots is proposed using the nominal model of the robot supplier incorporated into its controller.

A Systematic Approach for Accuracy Design of Lower-Mobility Parallel Mechanism

Robotica ◽  
2020 ◽  
Vol 38 (12) ◽  
pp. 2173-2188
Author(s):  
Wenjie Tian ◽  
Ziqian Shen ◽  
Dongpo Lv ◽  
Fuwen Yin
Keyword(s):  
Parallel Mechanism ◽  
Screw Theory ◽  
Geometric Error ◽  
Error Modeling ◽  
Tolerance Allocation ◽  
Design Stage ◽  
Geometric Errors ◽  
End Effector ◽  
Allocation Method ◽  
Lower Mobility

SUMMARYGeometric accuracy is a critical performance factor for parallel robots, and regardless of error compensation, accuracy design or tolerance allocation is another way to ensure the pose accuracy of a robot at design stage. A general method of both geometric error modeling and accuracy design of lower-mobility parallel mechanisms is presented. First, a general approach for error modeling of lower-mobility parallel mechanism is proposed based on screw theory, and then the geometric errors affecting the compensatable and uncompensatable accuracy of the end-effector are separated using the properties of dual vector space. The pose error aroused by compensatable geometric errors can be compensated via kinematic calibration, while the uncompensatable geometric errors should be minimized during the manufacturing and assembly processes. Based on that, the tolerance allocation method is presented, giving each uncompensatable geometric error a proper tolerance by the use of reliability theory. Compared with the traditional tolerance allocation method, the advantages of the proposed method are as follows: the number of geometric errors to be allocated is greatly reduced; the results of serialized tolerance allocation can be obtained according to different reliability indices of pose accuracy of end-effector for designers to choose; on the premise of guaranteeing the same pose accuracy of end-effector, the allocated tolerances are loose and easy to realize. Finally, the proposed methods are successfully applied to an R(2-RPS&RP)&UPS lower-mobility parallel robot, and the effectiveness and practicability of the proposed method are verified.

Kinematic modeling and parameter identification for a heavy gantry-type automated fiber placement machine considering gravity deformation

2020 ◽  
pp. 095440622094572
Author(s):  
Jianbo Wu ◽  
Liang Cheng ◽  
Yunbo Bi ◽  
Jiangxiong Li ◽  
Yinglin Ke
Keyword(s):  
Parameter Identification ◽  
Kinematic Model ◽  
Measurement Data ◽  
Joint Interface ◽  
Deformation Model ◽  
Kinematic Modeling ◽  
Fiber Placement ◽  
Position Errors ◽  
Automated Fiber Placement ◽  
Placement Machine

Automated fiber placement machine is the key equipment for low-cost and automated manufacturing of high-performance carbon composite materials. In order to meet the required position accuracy of fiber placement, this paper focuses on the kinematic modeling and parameter identification of the automated fiber placement machine. A kinematic model taking account of geometric deviations is established firstly. Since joint interfaces are the main origin of gravity deformation in a machine tool, an elastic beam deformation model is introduced to represent the joint interface, and then the former kinematic model is modified by analytical expressions of the gravity deformation for each joint interface. Based on the measurement data and the Levenberg-Marquardt optimization method, the parameter identification of the kinematic model is realized, and main issues such as measurement data selection, objective function definition are discussed. Finally, a kinematic calibration experiment is performed, and the experimental results verify the feasibility and validity of the modeling method. The position errors in Z direction of the automated fiber placement machine are effectively reduced by over 80%, which suggests that the proposed method reduces the effect of the gravity deformation and improves the accuracy of the automated fiber placement machine.

Sign in / Sign up

Export Citation Format

Share Document