Geometric accuracy design and error compensation of a one-translational and three-rotational parallel mechanism with articulated traveling plate

2017 ◽  
Vol 232 (12) ◽  
pp. 2083-2097 ◽  
Author(s):  
Tao Sun ◽  
Panfeng Wang ◽  
Binbin Lian ◽  
Sida Liu ◽  
Yapu Zhai
Keyword(s):  
Error Compensation ◽  
Parallel Mechanism ◽  
Screw Theory ◽  
Geometric Error ◽  
Error Modeling ◽  
Geometric Errors ◽  
Kinematic Calibration ◽  
Geometric Accuracy ◽  
Improvement Strategy ◽  
Accuracy Improvement

The demands for advanced and flexible docking equipment are increasing in the fields of aerospace, shipbuilding and construction machinery. Position and orientation accuracy is one of the most important criteria, which would directly affect the docking quality. Taking a novel one-translational and three-rotational docking equipment, referred to as PaQuad parallel mechanism as example, this article proposed an accuracy improvement strategy by geometric accuracy design and error compensation. Drawing mainly on screw theory, geometric error modeling of PaQuad parallel mechanism was first carried out via four independent routes. Joint perturbations and geometric errors were included in each route error twist. Wrenches due to articulated traveling plate were applied to eliminate joint perturbations. Then, geometric accuracy design was implemented at component and substructure levels. The basic principle was to transfer geometric errors into dimensional or geometric tolerance. High-precision machining/assembling techniques were applied to satisfy the tolerance. Finally, error compensation resorting to kinematic calibration was implemented at mechanism level. It can be summarized as identification modeling, measurement planning, and parameter identification and modification. Maximum deviations of PaQuad parallel mechanism before calibration experiment were 0.01 mm, [Formula: see text], [Formula: see text], and [Formula: see text]. And they become 0.01 mm, [Formula: see text], [Formula: see text], and [Formula: see text] after kinematic calibration. Orientation accuracy of PaQuad parallel mechanism has improved one order of magnitude. It proves the effectiveness of accuracy improvement in terms of geometric accuracy design and error compensation.

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.

A General Approach for Geometric Error Modeling of Lower Mobility Parallel Manipulators

2011 ◽  
Vol 3 (2) ◽  
Author(s):  
Haitao Liu ◽  
Tian Huang ◽  
Derek G. Chetwynd
Keyword(s):  
Systematic Approach ◽  
Parallel Manipulators ◽  
Geometric Error ◽  
Error Modeling ◽  
Kinematic Calibration ◽  
Accuracy Improvement ◽  
Linear Map ◽  
Homogeneous Transformation Matrix ◽  
Lower Mobility ◽  
Source Errors

This paper presents a general and systematic approach for geometric error modeling of lower mobility manipulators. The approach can be implemented in three steps: (1) development of a linear map between the pose error twist and source errors within an individual limb using the homogeneous transformation matrix method; (2) formulation of a linear map between the pose error twist and the joint error intensities of a lower mobility parallel manipulator; and (3) combination of these two models. The merit of this approach lies in that it enables the source errors affecting the compensatable and uncompensatable pose accuracy of the platform to be explicitly separated, thereby providing designers and/or field engineers with an informative guideline for the accuracy improvement achievable by suitable measures, i.e., component tolerancing in design, manufacturing and assembly processes, and kinematic calibration. Three typical and well-known parallel manipulators are taken as examples to illustrate the generality and effectiveness of this approach.

Geometric error compensation method based on Floyd algorithm and product of exponential screw theory

2016 ◽  
Vol 232 (7) ◽  
pp. 1156-1171 ◽  
Author(s):  
Qiang Cheng ◽  
Bingwei Sun ◽  
Zhifeng Liu ◽  
Qiunan Feng ◽  
Peihua Gu
Keyword(s):  
Error Compensation ◽  
Machine Tools ◽  
Screw Theory ◽  
Cost Effective ◽  
Geometric Error ◽  
Error Modeling ◽  
Compensation Method ◽  
Machining Accuracy ◽  
Distance Method ◽  
Five Axis

Error compensation technique is a recognized and cost-effective method to improve machining accuracy of machine tools. In this article, a new compensation method for geometric error is proposed based on Floyd algorithm and product of exponential screw theory. Based on topological structure and measured data, volumetric geometric error modeling is established by product of exponential screw theory. Then, the improved Floyd minimum-distance method was used to establish an error compensation model by adjusting weight unceasingly. In order to verify the effectiveness and generality of the method proposed in this article, two experiments were designed. A total of 5 five-axis machining centers of the same type with different use time were selected to carry out the simulation experiments. Results show that the Floyd method can provide higher compensation precision, that is, Floyd algorithm compensation method can keep positioning errors within the range [−8 µm, 9 µm]. In addition, roundness error, coaxial error, and surface roughness were reduced in the actual machining experiments of two machined conical tables. Therefore, it can be seen that the proposed compensation method is effective to improve machining accuracy of machine tools.

Modeling and Identification of Geometric Error Based on Screw Theory

2014 ◽  
Vol 941-944 ◽  
pp. 2219-2223 ◽  
Author(s):  
Guo Juan Zhao ◽  
Lei Zhang ◽  
Shi Jun Ji ◽  
Xin Wang
Keyword(s):  
Machine Tool ◽  
Laser Interferometer ◽  
Screw Theory ◽  
Geometric Error ◽  
New Method ◽  
Geometric Errors ◽  
Volumetric Error ◽  
B Spline ◽  
The Individual

In this paper, a new method is presented for the identification of machine tool component errors. Firstly, the Non-Uniform Rational B-spline (NURBS) is established to represent the geometric component errors. The individual geometric errors of the motion parts are measured by laser interferometer. Then, the volumetric error for a machine tool with three motion parts is modeled based on the screw theory. Finally, the simulations and experiments are conducted to confirm the validity of the proposed method.

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.

scholarly journals Geometric Error Modeling of Machine Tools Based on Screw Theory

2011 ◽  
Vol 24 ◽  
pp. 845-849 ◽  
Author(s):  
Zhao Yu ◽  
Li Tiemin ◽  
Tang Xiaoqiang
Keyword(s):  
Machine Tools ◽  
Screw Theory ◽  
Geometric Error ◽  
Error Modeling

An investigation on modeling and compensation of synthetic geometric errors on large machine tools based on moving least squares method

2016 ◽  
Vol 232 (3) ◽  
pp. 412-427 ◽  
Author(s):  
Zihan Li ◽  
Wenlong Feng ◽  
Jianguo Yang ◽  
Yiqiao Huang
Keyword(s):  
Machine Tool ◽  
Least Squares ◽  
Error Compensation ◽  
Machine Tools ◽  
Geometric Error ◽  
Moving Least Squares ◽  
Geometric Errors ◽  
Position Accuracy ◽  
Type Machine ◽  
Large Machine

This article intends to provide an efficient modeling and compensation method for the synthetic geometric errors of large machine tools. Analytical and experimental examinations were carried out on a large gantry-type machine tool to study the spatial geometric error distribution within the machine workspace. The result shows that the position accuracy of the tool-tip is affected by all the translational axes synchronously, and the position error curve shape is non-linear and irregular. Moreover, the angular error combined with Abbe’s offset during the motion of a translational axis would cause Abbe’s error and generate significant influence on the spatial positioning accuracy. In order to identify the combined effect of the individual error component on the tool-tip position accuracy, a synthetic geometric error model is established for the gantry-type machine tool. Also, an automatic modeling algorithm is proposed to approximate the geometric error parameters based on moving least squares in combination with Chebyshev polynomials, and it could approximate the irregular geometric error curves with high-order continuity and consistency with a low-order basis function. Then, to implement real-time error compensation on large machine tools, an intelligent compensation system is developed based on the fast Ethernet data interaction technique and external machine origin shift, and experiment validations on the gantry-type machine tool showed that the position accuracy could be improved by 90% and the machining precision could be improved by 85% after error compensation.

A Review of Geometric Error Modeling and Error Detection for CNC Machine Tool

2013 ◽  
Vol 303-306 ◽  
pp. 627-631 ◽  
Author(s):  
Zhen Yu Han ◽  
Hong Yu Jin ◽  
Yu Long Liu ◽  
Hong Ya Fu
Keyword(s):  
Machine Tool ◽  
Error Detection ◽  
Error Compensation ◽  
Machine Tools ◽  
Performance Criterion ◽  
Geometric Error ◽  
Error Modeling ◽  
Cnc Machine Tool ◽  
Cnc Machine ◽  
Error Sources

Error compensation can improve the accuracy of machine tools effectively. Among the error sources affecting the accuracy of CNC machine tool, geometric error is always set as a key performance criterion. This paper summarizes several methods of geometric error modeling and reviews the characteristics of different methods. Furthermore, available methods for measuring geometric errors have been reviewed also based on the advanced instruments. This work aims at enhancing the efficiency of error detection and give a perspective for the application of error compensation in the future.

Geometric Error Modeling of a Vertical Machining Center

2013 ◽  
Vol 694-697 ◽  
pp. 1842-1845
Author(s):  
Gui Qiang Liang ◽  
Jun Xian Zhang ◽  
Fei Fei Zhao
Keyword(s):  
Coordinate Transformation ◽  
Transformation Method ◽  
Geometric Error ◽  
Error Modeling ◽  
Machining Accuracy ◽  
Geometric Errors ◽  
Lower Body ◽  
Body System ◽  
Machining Center ◽  
Multi Body

The effect of geometric error on machining accuracy was researched by multi-body system theory, as well as homogeneous coordinate transformation method. Taking a vertical machining center as example, topological structure of the machine tool was described by lower body array. Lower body array of the machining center, motion freedom between adjacent bodies and geometric errors of the vertical machining center were analyzed. Geometric errors of the bodies in the multi-body system were expressed by homogeneous coordinate transformation. Error model for machining accuracy was deduced and geometric errors having influence on the machining accuracy were identified. The research results provide guidance for analyze of geometric errors on machining accuracy.

scholarly journals Accuracy Improvement Calibrations for the Double-Position 4-PPPS Aircraft Docking System

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Ruolong Qi ◽  
Yuangui Tang ◽  
Ke Zhang
Keyword(s):  
Parallel Mechanism ◽  
Calibration Method ◽  
Labor Intensity ◽  
Kinematic Calibration ◽  
Kinematic Parameters ◽  
Accuracy Improvement ◽  
Pointing Error ◽  
Accuracy Measurement ◽  
Aircraft Fuselage ◽  
Docking Experiment

A double-positions 4-PPPS parallel mechanism is used for the aircraft fuselage assembly process to improve the docking efficiency and reduce the labor intensity. However, the accuracy is hard to guarantee, for the mechanism is large and redundant and has manufacturing and assembly errors. To improve the accuracy of the 4-PPPS parallel aircraft fuselage docking system, firstly, an averaging iteration method is proposed to calibrate the datum points in the airplane coordinate which are the references of the entire docking system. And secondly, a kinematic calibration method based on the derivative of the spatial pose transformation is proposed to calibrate up to 42 kinematic parameters. By these two methods, the final maximum position error reduced from 2.2 mm to 0.035 mm and the maximum pointing error reduced from 0.08 degree to 0.018 degree. The accuracy measurement and docking experiment prove the efficiency of the proposed methods.

Sign in / Sign up

Export Citation Format

Share Document