Study on Structural Error Compensation of 3-UPU Parallel Mechanism

2020 ◽  
Vol 13 (8) ◽  
pp. 1266-1274
Author(s):  
Yonggeng Wei ◽  
Xin Shi ◽  
Zhongxian Wang
Keyword(s):  
Error Compensation ◽  
Parallel Mechanism ◽  
Least Squares Method ◽  
Numerical Control ◽  
Parallel Mechanisms ◽  
Connecting Rod ◽  
Position Change ◽  
Positioning Accuracy ◽  
Solution Equation ◽  
Moving Platform

Background: Compared with the traditional series mechanism, the parallel mechanism has a better kinematic performance. Structural size error is the main factor affecting the accuracy of parallel mechanisms. Objective: The paper mainly studies the compensation of the rod length error, the moving platform radius error and the fixed platform radius error of 3-UPU parallel mechanism. Methods: To establish a generalized forward and inverse solution equation with error compensation, the position change of the moving platform is measured by a laser interferometer, and the change amount of the three connecting rod lengths at the corresponding position is recorded. Optimized by least squares method, the optimized error compensation values are compensated to the kinematics algorithm of the numerical control system, and the positioning accuracy is improved. Results: The results show that the positioning accuracy is higher when the mechanism moves in the lower plane, and the positioning error in the z axis direction is smaller than x, y, y=x, y=-x axis. Conclusion: After the error compensation, the overall positioning accuracy of the mechanism is increased by 60%.

The Parallel Mechanism and Variable Acceleration Control Method

2013 ◽  
Vol 579-580 ◽  
pp. 659-664
Author(s):  
Xiang Bo Ouyang ◽  
Ke Tian Li ◽  
Hong Jian Xia ◽  
Su Juan Wang ◽  
Huan Wei Zhou ◽  
...  
Keyword(s):  
Parallel Mechanism ◽  
Control Method ◽  
The Other ◽  
Connecting Rod ◽  
Motion Platform ◽  
The Third ◽  
Symmetric Structure ◽  
Slide Block ◽  
Operation Process ◽  
Moving Platform

t presents the parallel mechanism and variable acceleration control method, which is composed of slider, connecting rod, moving platform and linear guide etc. The motion platform is supported by three connecting rods through hinging, the other end of the connecting rods are respectively hinged with two sliders. Among them two pairs of connecting rod, two sliders and the moving platform formed a symmetric structure that is the so called Parallel Mechanism. The third connecting rod is parallel to one of two connecting rods, so that the two parallel connecting rods, slide block and the moving platform formed a parallelogram structure, it makes that the moving platform is always parallel to liner guiderail in the process of movement. By controlling the two sliders moving in the way of variable acceleration, it can make the trajectory curve, speed curve and acceleration curve of the moving platform are continuous, smooth, so impact and vibration of the moving platform is limited in the operation process.

scholarly journals Reconfiguration Analysis of a 3-DOF Parallel Mechanism

Robotics ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 66
Author(s):  
Maurizio Ruggiu ◽  
Xianwen Kong
Keyword(s):  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Operation Mode ◽  
Parallel Mechanisms ◽  
Universal Joint ◽  
Kinematic Chains ◽  
Constraint Equations ◽  
The Third ◽  
Equilateral Triangles ◽  
Moving Platform

This paper deals with the reconfiguration analysis of a 3-DOF (degrees-of-freedom) parallel manipulator (PM) which belongs to the cylindrical parallel mechanisms family. The PM is composed of a base and a moving platform shaped as equilateral triangles connected by three serial kinematic chains (legs). Two legs are composed of two universal (U) joints connected by a prismatic (P) joint. The third leg is composed of a revolute (R) joint connected to the base, a prismatic joint and universal joint in sequence. A set of constraint equations of the 1-RPU−2-UPU PM is derived and solved in terms of the Euler parameter quaternion (a.k.a. Euler-Rodrigues quaternion) representing the orientation of the moving platform and of the Cartesian coordinates of the reference point on the moving platform. It is found that the PM may undergo either the 3-DOF PPR or the 3-DOF planar operation mode only when the base and the moving platform are identical. The transition configuration between the operation modes is also identified.

A New Direct Deformation Measurement System to Enhance Positioning Accuracy of Machine Tools

2006 ◽  
Author(s):  
Paolo Bosetti ◽  
Francesco Biral ◽  
Enrico Bertolazzi ◽  
Mariolino De Cecco
Keyword(s):  
Measurement System ◽  
Displacement Field ◽  
Error Compensation ◽  
Manufacturing Systems ◽  
Numerical Control ◽  
Structural Deformation ◽  
Underlying Structure ◽  
Physical Point ◽  
Positioning Accuracy ◽  
Structural Deformations

The positioning accuracy of computer numerical control machines tools and manufacturing systems is affected by structural deformations, especially for large sized systems. Heat induced deformations, long-period deformation of foundations, and the manufacturing process itself, cause time-dependent structural deformations of the machine body, which are difficult to model and predict. In fact, the feasibility of a model-based error prediction is often limited by the complexity of the problem from both the geometrical and the physical point of view. As a consequence, only limited success has been achieved in active error compensation based on the modeling of the relationship between the generalized dynamic loads and the structural deformation field. This paper illustrates a different approach in active error compensation, which exploits a new measurement system, currently in the patenting process, able to measure, in real time, the machine structural displacement field, without any model for the dynamic structural behavior. The first part of the paper illustrates the working principle of the measurement system, which can be described as coupled hardware and software subsystems. The hardware subsystem is basically a triangular mesh of struts, whose nodes are rigidly connected to the underlying structure under measurement. The struts are instrumented with Fibre-optic Bragg Gratings providing their longitudinal strain values. The software part is an algorithm, which evaluates the discrete displacement field by computing the node positions on the basis of the strut longitudinal deformations. The second part of the work focuses on the performance, in terms of accuracy, resolution, and time stability, of a prototype of the above described measurement system. Finally, the third part illustrates two major enhancements on the system design: the design of a monolithic variant of the reticular structure (with higher performances and reduced cost), and a different computation algorithm providing increased accuracy and limited error propagation.

Dynamic accuracy analysis of a 5PSS/UPU parallel mechanism based on rigid-flexible coupled modeling

2020 ◽  
Author(s):  
Yanbiao Li ◽  
Zesheng Wang ◽  
Chaoqun Chen ◽  
Taotao Xu ◽  
Bo Chen
Keyword(s):  
Finite Element ◽  
Root Mean Square ◽  
Parallel Mechanism ◽  
Research Work ◽  
Accuracy Analysis ◽  
Mean Square ◽  
Parallel Mechanisms ◽  
Connecting Rod ◽  
Dynamic Accuracy ◽  
Mean Square Errors

Abstract In order to improve the low output accuracy caused by the elastic deformations of the branch chains, a finite element-based dynamic accuracy analysis method for parallel mechanisms is proposed in this paper. First, taking a 5–prismatic–spherical–spherical (PSS)/universal–prismatic–universal (UPU) parallel mechanism as an example, the error model is established by a closed vector chain method while its influence on the dynamic accuracy of the parallel mechanism is analyzed through numerical calculation and simulation. According to the structural and error characteristics of the parallel mechanism, a vector calibration algorithm is proposed to reduce the position and pose errors along the whole motion trajectory. Then, considering the elastic deformation of the rod, the rigid-flexible coupling dynamic equations of the mechanism are established by combining the finite element method with the Lagrange method, and the equations are vectorially superimposed by means of internal force cancellation to synthesize the elastic dynamics equation of the connecting rod. Based on the constraint condition of each moving part, the elastodynamic model of the whole machine is obtained. Furthermore, the effect of component flexibility on the dimensionless root mean square error of the displacement, velocity and acceleration of the moving platform is investigated by using a Newmark method, and the dynamic accuracy influenced by these dimensionless root mean square errors is further studied. The research work establishes an important theoretical foundation for the development of the prototype.

Error Analysis of a 2-PRS/2-UPS 4-DOF Parallel Platform

2012 ◽  
Vol 605-607 ◽  
pp. 1511-1514
Author(s):  
Shan Le Cai ◽  
Li Bing Peng ◽  
Wen Tao Huang
Keyword(s):  
Error Compensation ◽  
Parallel Mechanism ◽  
Theoretical Foundation ◽  
Error Modeling ◽  
Vector Method ◽  
Joint Point ◽  
Structural Error ◽  
New Type ◽  
Parallel Platform ◽  
Moving Platform

A new type of a 2-PRS/2-UPS 4-DOF parallel platform was introduced. The error model of the parallel worktable was established through the vector method. The effect of structural error, driving error, position error and clearance error of the joint point to the pose error of the moving platform can be analyzed. Error modeling provides theoretical foundation for design and error compensation of the parallel mechanism.

Block Adjacency Matrix Method for Analyzing the Configuration Transformations of Metamorphic Parallel Mechanisms

2014 ◽  
Author(s):  
Duanling Li ◽  
Chunxia Li ◽  
Zhonghai Zhang ◽  
Xianwen Kong
Keyword(s):  
Adjacency Matrix ◽  
Matrix Method ◽  
Parallel Mechanism ◽  
New Method ◽  
Parallel Mechanisms ◽  
Adjacency Matrices ◽  
Moving Platform ◽  
Internal Configuration ◽  
Spherical Motion ◽  
Metamorphic Mechanisms

Metamorphic transformation is a fundamental and key issue in the design and analysis of metamorphic mechanisms. It is tedious to represent and calculate the metamorphic transformations of metamorphic parallel mechanisms using the existing adjacency matrix method. To simplify the configuration transformation analysis, we propose a new method based on block adjacency matrix to analyze the configuration transformations of metamorphic parallel mechanisms. A block adjacency matrix is composed of three types of elements, including limb matrices that are adjacency matrices each representing a limb of a metamorphic parallel mechanism, row matrices each representing how a limb is connected to the moving platform, and column matrices each representing how a limb is connected to the base. Manipulations of the block adjacency matrix for analyzing the metamorphic transformations are presented systematically. If only the internal configuration of a limb changes, the configuration transformations can be obtained by simply calculating the corresponding limb matrix. A 3-URRRR metamorphic parallel mechanism, which has five configurations including a 1-DOF translation configuration and a 3-DOF spherical motion configuration, is taken as an example to illustrate the effectiveness of the proposed approach to the metamorphic transformation analysis of metamorphic parallel mechanism.

scholarly journals Positioning Accuracy Analysis of the Parallel Mechanism Near Singular Positions

2015 ◽  
Vol 20 (1) ◽  
pp. 5-18 ◽  
Author(s):  
J. Bałchanowski
Keyword(s):  
Numerical Modelling ◽  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Accuracy Analysis ◽  
Parallel Mechanisms ◽  
Contact Interactions ◽  
Positioning Accuracy ◽  
Singular Configurations ◽  
Positioning Errors ◽  
Three Degrees Of Freedom

Abstract This paper presents a method of numerical modelling of parallel mechanisms with clearances in their kinematic pairs taken into account. The pairs with clearances are modelled as shape connections based on constraints in the form of contact interactions. Using the created models simulations were run to determine the positioning errors of the links in a parallel mechanism with three degrees of freedom (MR2120). In particular, the accuracy of positioning the links close to the mechanism singular configurations was studied.

scholarly journals Kinematic analysis of a novel 3-CRU translational parallel mechanism

2015 ◽  
Vol 6 (1) ◽  
pp. 57-64 ◽  
Author(s):  
B. Li ◽  
Y. M. Li ◽  
X. H. Zhao ◽  
W. M. Ge
Keyword(s):  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Jacobian Matrix ◽  
Screw Theory ◽  
Structural Characteristics ◽  
Parallel Mechanisms ◽  
Reachable Workspace ◽  
Potential Applications ◽  
Moving Platform ◽  
And Performance

Abstract. In this paper, a modified 3-DOF (degrees of freedom) translational parallel mechanism (TPM) three-CRU (C, R, and U represent the cylindrical, revolute, and universal joints, respectively) structure is proposed. The architecture of the TPM is comprised of a moving platform attached to a base through three CRU jointed serial linkages. The prismatic motions of the cylindrical joints are considered to be actively actuated. Kinematics and performance of the TPM are studied systematically. Firstly, the structural characteristics of the mechanism are described, and then some comparisons are made with the existing 3-CRU parallel mechanisms. Although these two 3-CRU parallel mechanisms are both composed of the same CRU limbs, the types of freedoms are completely different due to the different arrangements of limbs. The DOFs of this TPM are analyzed by means of screw theory. Secondly, both the inverse and forward displacements are derived in closed form, and then these two problems are calculated directly in explicit form. Thereafter, the Jacobian matrix of the mechanism is derived, the performances of the mechanism are evaluated based on the conditioning index, and the performance of a 3-CRU TPM changing with the actuator layout angle is investigated. Thirdly, the workspace of the mechanism is obtained based on the forward position analysis, and the reachable workspace volume is derived when the actuator layout angle is changed. Finally, some conclusions are given and the potential applications of the mechanism are pointed out.

Classification of 3-DOF 3-UPU Translational Parallel Mechanisms Based on Constraint Singularity Loci Using Gröbner Cover

2021 ◽  
Author(s):  
Xianwen Kong
Keyword(s):  
Parallel Mechanism ◽  
Polynomial Systems ◽  
Coordinate Frame ◽  
Parallel Mechanisms ◽  
Systematic Classification ◽  
Starting Point ◽  
Moving Platform ◽  
Singular Configuration ◽  
The Impact

Abstract A 3-UPU translational parallel mechanism (TPM) is one of typical TPMs. Several types of 3-UPU TPMs have been proposed in the literature. Despite comprehensive studies on 3-UPU TPMs in which the joint axes on the base and the moving platform are coplanar, only a few 3-UPU TPMs with a skewed base and moving platform have been proposed. However, the impact of link parameters on singularity loci of such TPMs has not been systematically investigated. The advances in computing CGS (comprehensive Gröbner system) or Gröbner cover of parametric polynomial systems provide an efficient tool for solving this problem. This paper presents a systematic classification of 3-UPU TPMs, especially those with a skewed base and moving platform, based on constraint singularity loci. First, the constraint singularity equation of a 3-UPU TPM is derived. To simplify this equation, the coordinate frame on the base (or moving platform) is set up such that the centers of three U joints are located on different coordinate axes. Using Gröbner Cover, the 3-UPU TPMs are classified into 20 types based on the constraint singularity loci. Finally, a novel 3-UPU TPM is proposed. Unlike most of existing 3-UPU TPMs which can transit to two or more 3-DOF operation modes at a constraint singular configuration, the proposed 3-UPU TPM can only transit to one general 3-DOF operation mode in a constraint singular configuration. The singularity locus divides the workspace of this 3-UPU TPM into two constraint singularity-free regions. This work provides a solid foundation for the design of 3-UPU TPMs and a starting point for the classification of a general 3-UPU parallel mechanism.

The Accuracy Analysis of Parallel Mechanism Assembly Robot

2013 ◽  
Vol 423-426 ◽  
pp. 2769-2775 ◽  
Author(s):  
Xin Rong Liu
Keyword(s):  
Parallel Mechanism ◽  
Joint Angle ◽  
Parallel Robot ◽  
Accuracy Analysis ◽  
Analysis Model ◽  
Error Sources ◽  
Positioning Accuracy ◽  
Moving Platform ◽  
Position And Orientation ◽  
High Repeatability

Parallel robot has the advantages of high rigidity,high bearing capacity and high repeatability of positioning accuracy,and make it more and more widely used in the field of industrial applications.In this paper,the 3-RRR parallel mechanism assembly robot was used as the research object;introduced the sources of error in the parallel mechanism operation platform's position and orientation,furthermore,analyzed the factors of the error sources;then built up that parallel robot's error analysis model,solved the error model with the differential equation,and analyzed the error of parallel robot's structural in rod length,joint angle,the moving platform and the base platform's radius of circle,then simulated with MATLAB.Research shows that All structure errors in parallel mechanism increased by the X axis monotone increasing.

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