Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 2: Generalized Transfer Functions

1998 ◽  
Vol 120 (3) ◽  
pp. 632-639 ◽  
Author(s):  
S. Fraser ◽  
M. H. Attia ◽  
M. O. M. Osman
Keyword(s):  
Finite Element ◽  
Machine Tool ◽  
Real Time ◽  
Thermal Deformation ◽  
Transfer Functions ◽  
Design Stage ◽  
Machining Accuracy ◽  
Deformation Problem ◽  
Machine Tool Structure ◽  
Machine Tool Structures

With the ever increasing demand for higher machining accuracy at lower cost, thermal deformation of machine tool structures has to be minimized at the design stage, and compensated for during operation. To compensate for this type of error, two real-time process models are required to identify the magnitude of the transient thermal load and to estimate the relative thermal displacement between the tool and the work piece. Special considerations should be given to the solution of the first ill-posed inverse heat conduction model IHCP. In this paper, the concept of generalized modelling is extended to the thermal deformation problem. The results of this analysis is used to develop expressions for the generalized transfer functions of the thermal, and thermal deformation response of the machine tool structure. These transfer functions are the basic building blocks for real-time solution of the IHCP and then the deformation problem. The latter acts as a feed-back signal to the control system. Finite element simulation of the temperature field and the thermal deformation of a machine tool structure confirmed that the generalized transfer function approach can reproduce the accuracy of the finite element model but two orders of magnitude faster.

Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 5: Experimental Verification

1999 ◽  
Vol 121 (3) ◽  
pp. 517-523 ◽  
Author(s):  
S. Fraser ◽  
M. H. Attia ◽  
M. O. M. Osman
Keyword(s):  
Control System ◽  
Machine Tool ◽  
Thermal Deformation ◽  
Transfer Functions ◽  
Integrated System ◽  
Design Stage ◽  
Machining Accuracy ◽  
Deformation Model ◽  
Component Structure ◽  
Artificial Heat

Machining accuracy is more often governed by thermal deformation of the machine tool structure than by static stiffness and dynamic rigidity. Since thermally induced errors cannot completely be eliminated at the design stage, the use of control and compensation systems is an inevitable course of action. Existing control systems are based on two different approaches; the use of empirical compensation function, and on-line execution of numerical simulation models. To overcome the limitations of these methods, a new control system has recently been proposed by the authors. This system, which is based on the concept of generalized modelling, incorporates a realtime inverse heat conduction problem IHCP solver to estimate the transient thermal load applied to the structure. With this information, the relative thermal deformation between the tool and the workpiece is estimated and used as a feedback control signal. In previous parts of this series, computer simulation test cases were carried out to examine the dynamic response, accuracy and stability of the system. In the present study, the performance of various components of the control system, specifically, the IHCP solver, the thermal deformation estimator, and the feedback controller are verified experimentally using a three-component structure. The results showed that the derived generalized thermoelastic transfer functions and algorithms are indeed quite accurate in predicting and controlling the transient thermoelastic response behaviour of a predominantly linear structure. The results showed that the a IHCP solver is inherently stable even when the temperature measurements are contaminated with random errors. The excellent computational efficiency of the integrated system is shown to be well suited for real-time control applications involving multi-dimensional structures, achieving a control cycle of less than 0.5 second. The experimental results showed that in real structures higher modes can be present, and therefore, a fourth order deformation model should be used to improve the prediction accuracy. The proposed PID control system, with feedforward branches, was capable of reducing thermal deformations of the order of 200 μm to levels below ±8 μm. These results also demonstrated the effectiveness of artificial heat sources as a control actuation mechanism, in spite of their inherent limitations, namely, thermal inertia, coupledness, and unidirectionality.

Real-Time Adaptive Modeling Approach to Compensate the Thermal Deformation of Nonlinear Machine Tool Structures

2004 ◽  
Author(s):  
S. Fraser ◽  
Helmi Attia ◽  
M. O. M. Osman
Keyword(s):  
Machine Tool ◽  
Temperature Measurement ◽  
Real Time ◽  
Thermal Deformation ◽  
Operating Conditions ◽  
Design Stage ◽  
Frequency Noise ◽  
Adaptive Modeling ◽  
Wide Range ◽  
Machine Tool Structures

Machine tool structures cannot be fully optimized at the design stage to cover the wide range of operating conditions. Therefore, reliable control systems emerge as the logical solution to compensate for thermal errors. Due to the difficulty of measuring the relative thermal displacement δ between the tool and the workpiece during machining, δ has to be accurately estimated in real-time. A new concept of adaptive modeling is introduced to develop control-based dynamic models to predict and compensate for thermal deformation of nonlinear complex machine tool structures. A key element of this approach is to replace the changes in the contact pressures along the joint by fictitious contact heat sources FCHS. This allows us to track the system nonlinearity through temperature measurements and real-time inverse heat conduction IHCP solution. The proposed approach dealt successfully with a number of challenges; namely, the non-uniqueness of the problem, and the lack of sufficient conditions to identify each of such unusual FCHS separately. The results showed that the models are capable of satisfying the accuracy, stability and computational efficiency requirements, even when the temperature measurement signal is contaminated with random noise. The results also showed that the thermal deformation transfer function behaves as low-pass filters, and as such it attenuates the high frequency noise associated with temperature measurement error.

Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 1: Concept of Generalized Modelling

1998 ◽  
Vol 120 (3) ◽  
pp. 623-631 ◽  
Author(s):  
S. Fraser ◽  
M. H. Attia ◽  
M. O. M. Osman
Keyword(s):  
Machine Tool ◽  
Thermal Deformation ◽  
Infinite Plate ◽  
Measurement Data ◽  
Design Stage ◽  
Machining Accuracy ◽  
Generalized Model ◽  
Real Process ◽  
Machine Tool Structures ◽  
Transient Thermal

With the increasing demand for improved machining accuracy in recent years, the problem of thermal deformation of machine tool structures is becoming more critical than ever. In spite of the effort for improving the thermal deformation characteristics of machine tools at the design stage, there are always some residual errors that have to be compensated for during machining. The design of a generic multi-axis control system requires the development of two models to estimate the transient thermal load and to estimate the thermal deformation of the structure in real-time. To satisfy the stringent accuracy and stability requirements of these two models, a new concept of “generalized modelling” is introduced. It combines mathematical modelling with empirical calibration, and is based on the existence of a mathematical similarity between the real process and a simplified model, referred to as the fundamental generalized problem FGP. To obtain an analytical description of the heat transfer and thermal deformation processes in machine tool structures, an analytical solution of the FGP, which consists of an infinite plate with a central ring heat source, is derived using Hankel transformation. Computer-simulated test cases are presented to demonstrate the use of generalized modelling for predicting the transient thermal response in a complex machine tool structure. It was also shown how the generalized model can accurately extrapolate limited measurement data to predict the entire temperature field. The results confirmed that the generalized model can reproduce the accuracy of the finite-element solution, but two orders of magnitude faster.

Study on the Thermal Characteristics Simulation and Error Compensation of Long Rail of Heavy Numerically-Controlled Machine Tool

2014 ◽  
Vol 577 ◽  
pp. 187-191
Author(s):  
Ming Yue Xiao ◽  
Zhong Ping Hua ◽  
Shui Sheng Cheng
Keyword(s):  
Finite Element ◽  
Machine Tool ◽  
Error Compensation ◽  
Thermal Deformation ◽  
Thermal Characteristics ◽  
Machining Accuracy ◽  
Guide Rail ◽  
Ansys Software ◽  
Working Process ◽  
Main Factors

In the working process of numerically-controlled machine tool, the generation of heat by friction between the guide rail and the workbench will cause the thermal deformation under the high temperature, which impacts on the machining accuracy of machine tool. Through the finite element modeling for the guide rail of machine tool by the ANSYS software, the thermal characteristics is simulated in the process of guide rail, then the main factors of thermal deformation is analyzed, finally the corresponding measures focusing on the error compensation is proposed.

Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 4: A Multi-Variable Closed-Loop Control System

1999 ◽  
Vol 121 (3) ◽  
pp. 509-516 ◽  
Author(s):  
S. Fraser ◽  
M. H. Attia ◽  
M. O. M. Osman
Keyword(s):  
Control System ◽  
Machine Tool ◽  
Thermal Deformation ◽  
Closed Loop ◽  
Transfer Functions ◽  
Closed Loop Control ◽  
Loop Control ◽  
Closed Loop Control System ◽  
Loop Control System ◽  
Machine Tool Structures

A multi-variable closed-loop control system is proposed to compensate for the thermal deformation of machine tool structures. The control system recognizes the fact the relative thermal displacement between the tool and workpiece is not accessible for direct measurement. Using the generalized thermoelastic transfer functions of the structure, which provide satisfactory input-output dynamic dependencies, the heat input to the structure and thermal displacements are estimated in real time. Artificial heating elements are used as the actuation mechanism of the control system, since they provide an economical solution for retrofitting existing conventional machine tools, and can also be combined with NC controllers to effect the desired compensation of the expansion and bending modes of deformation. Computer simulation test results indicated that even when the random temperature measurement and power actuation errors are taken in consideration, an accuracy of better than 2.5 μm and a control cycle of the order of 1 second are achievable.

Mathematical Model for the Influence of Machine Tool Parts Deformation on Machining Accuracy

2014 ◽  
Vol 556-562 ◽  
pp. 1354-1357
Author(s):  
Li Gong Cui ◽  
Gui Qiang Liang ◽  
Fang Shao
Keyword(s):  
Mathematical Model ◽  
Mathematical Method ◽  
Machine Tool ◽  
Cutting Tool ◽  
Lower Surface ◽  
Design Stage ◽  
Machining Accuracy ◽  
Cutting Point ◽  
The Mathematical Model

This paper presents a mathematical method to analyze the influence of each machine tool part deformation on the machining accuracy. Taking a 3-axis machine tool as an example, this paper divides the machine tool into the cutting tool sub-system and workpiece sub-system. Taking the deformation of lower surface of the machine bed as the research target, the mathematical model of the deformation on the displacement of the cutting point was established. In order to distribute the stiffness of each part, the contribution degree of each part on the machining accuracy was analyzed. Using this mathematical model, the stiffness of each part can be distributed at the design stage of the machine tool, and the machining accuracy of the machine tool can be improved economically.

Exakte posenabhängige Strukurmodelle*/Accurate virtual machine tool structures - Online-identification of the general model of a lightweight machine tool structure with pose-dependent dynamic behavior

2017 ◽  
Vol 107 (05) ◽  
pp. 323-328
Author(s):  
S. Apprich ◽  
F. Wulle ◽  
A. Prof. Pott ◽  
A. Prof. Verl
Keyword(s):  
Machine Tool ◽  
Least Squares ◽  
Dynamic Behavior ◽  
Natural Frequencies ◽  
Recursive Least Squares ◽  
Machine Model ◽  
Online Identification ◽  
Working Space ◽  
Machine Tool Structure ◽  
Machine Tool Structures

Serielle Werkzeugmaschinenstrukturen weisen ein posenabhängiges, dynamisches Verhalten auf, wobei die Eigenfrequenzen um mehrere Hertz im Arbeitsraum variieren können. Die genaue Kenntnis dieses Verhaltens gestattet eine verbesserte Regelung der Strukturen. Ein generelles parametrisches Maschinenmodell, dessen Parameter online durch einen Recursive-Least-Squares-Algorithmus an das reale Maschinenverhalten angepasst werden, stellt Informationen über dieses Maschinenverhalten bereit.   Serial machine tool structures feature a pose-dependent dynamic behavior with natural frequencies varying by serveral hertz within the working space. The accurate knowledge of this behavior allows an improved control of the structures. A general parametric machine model, whose parameters are adapted online to the actual machine tool behavior by a Recursive Least Squares algorithm, provides information about the pose-dependent dynamic behavior.

scholarly journals Effect of Supply Cooling Oil Temperature in Structural Cooling Channels on the Positioning Accuracy of Machine Tools

2019 ◽  
Vol 35 (6) ◽  
pp. 887-900 ◽  
Author(s):  
K.-Y. Li ◽  
W.-J. Luo ◽  
M.-H. Yang ◽  
X.-H. Hong ◽  
S.-J. Luo ◽  
...  
Keyword(s):  
Machine Tool ◽  
Thermal Deformation ◽  
Thermal Error ◽  
Machining Accuracy ◽  
Feed System ◽  
Positioning Accuracy ◽  
Cooling Channels ◽  
Position Accuracy ◽  
Machine Tool Accuracy ◽  
Volume Method

ABSTRACTIn this study, the thermal deformation of a machine tool structure due to the heat generated during operation was analyzed, and embedded cooling channels were applied to exchange the heat generated during the operation to achieve thermal error suppression. Then, the finite volume method was used to simulate the effect of cooling oil temperature on thermal deformation, and the effect of thermal suppression was experimentally studied using a feed system combined with a cooler to improve the positioning accuracy of the machine tool. In this study, the supply oil temperature in the structural cooling channels was found to significantly affect the position accuracy of the moving table and moving carrier. If the supply oil temperature in the cooling channels is consistent with the operational ambient temperature, the position accuracy of the moving table in the Y direction and the moving carrier in the X and Z directions has the best performance under different feed rates. From the thermal suppression experiments of the embedded cooling channels, the positioning accuracy of the feed system can be improved by approximately 25.5 % during the dynamic feeding process. Furthermore, when the hydrostatic guideway is cooled and dynamic feeding is conducted, positioning accuracy can be improved by up to 47.8 %. The machining accuracy can be improved by approximately 60 % on average by using the embedded cooling channels in this study. Therefore, thermal suppression by the cooling channels in this study can not only effectively improve the positioning accuracy but also enhance machining accuracy, proving that the method is effective for enhancing machine tool accuracy.

Estimation of Dynamic Mechanical Error for Evaluation of Machine Tool Structures

2012 ◽  
Vol 6 (2) ◽  
pp. 147-153 ◽  
Author(s):  
Daisuke Kono ◽  
◽  
Sascha Weikert ◽  
Atsushi Matsubara ◽  
Kazuo Yamazaki ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Machine Tool ◽  
Driving Force ◽  
Inertial Force ◽  
Element Analysis ◽  
Simple Method ◽  
Dynamic Mechanical ◽  
Machine Tool Structures ◽  
Multi Body

Dynamic motion errors of machine tools consist of errors in the mechanical system and the servo system. In this study, a simple method to estimate the dynamic mechanical error is proposed to evaluate machine tool structures. The dynamic mechanical error in the low frequency range is estimated from the static deformation due to the driving force, the counter force, and the inertial force. The error in a high-precision machine tool is estimated for comparison with measurements. Two calculation tools, finite element analysis and rigid multi-body simulation, are used for the estimation. Measured dynamic mechanical errors can be correctly estimated by the proposed method using finite element analysis. The tilt of driven bodies is the major reason for dynamic mechanical errors. When the reduction factor representing the structural deformation is properly determined, the rigid multi-body simulation is also an effective tool. Use of the proposed method for modification planning is demonstrated. Stiffness enhancement of the saddle was an effective modification candidate to reduce the dynamic mechanical error. If the error should be reduced to sub-micrometer level, the location of components should be modified because the Abbe offset and the offset of the driving force from the inertial force must be shortened.

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