Among the thermal error sources of the high accuracy and efficiency machine tools, the thermal errors induced by the heat generated from running high speed motorized spindle is the crucial one. A new ...thermal error control method for motorized spindle is suggested, which is based on the thermal deformation balance principle. The essential idea of the method is to utilize the thermal contraction of Carbon Fiber Reinforced Plastic (CFRP) to restrain the thermal elongation of metal spindle housing. In the designed control system, the CFRP bars are uniformly distributed around the spindle housing, and the ThermoElectric Modules (TEMs) works as the heat pump which transfers the heat from spindle housing to CFRP bar. The experimental and numerical simulation results show that the suggested approach reduces 97% thermal displacement compared with the motorized spindle without the suggested thermal error control system. It is expected that the suggested method can also be applied to thermal error control for various cylindrical high-precision parts including aerospace equipment, optics and optical instruments.
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•The thermal error control system (TECS) for motorized spindle is designed.•The thermal contraction of CFRP restrains the thermal elongation of metal.•The TECS is based on the thermal deformation balance principle.•The effectiveness of TECS is validated by the experimental and FEM results.
The development of high-reliability, high-precision large-scale CNC ultra-precision grinding machines is essential for the efficient processing and manufacturing of large-diameter optical components. ...In this paper, we studied the reliability and the precision-maintenance of the ultra-precision grinding machine tool experimentally. First, the subsystems with poor performance were identified based on former operating data, which turned out to be the hydrostatic spindle subsystem and the feed subsystem. Then, we set up specific experimental platforms for these two subsystems to study the thermal deformation and thermal characteristics. The temperature difference between the inflow and outflow oils of the hydrostatic systems is used as the key parameter to model the accuracy evolution. Our results may provide a method to reveal the relationship between the thermal characteristics and the operating parameters of the subsystems, and therefore compensate the thermal error of the whole ultra-precision grinding machine.
Polymer concrete or epoxy granite is becoming more popular for beds, bases, and other structures of precision machine tools, owing to its excellent damping characteristics. To realize the same static ...rigidity as that of the cast-iron structures, steel-reinforced epoxy granite (SREG) structures are being used. The vast differences in the thermal properties of steel and epoxy granite (EG) are likely to cause higher magnitudes of thermal error. This work aims to investigate the thermal behaviour of a computerized numerical control (CNC) lathe built with a novel dynamically enhanced SREG bed and compare its performance with the lathe with a cast iron bed. Experimental and numerical investigations have been carried out under cross-feed (CF) drive idle running conditions to determine the TCP deformation. The results reveal that the thermal error in the CNC lathe with SREG bed is 1.68 times that of the lathe with cast iron (CI) bed at 20 ºC and 1.8 times at 40 ºC environmental temperature variation chamber (ETVC) conditions. It could be identified that the heat generated in the CF is conducted to the steel guideways embedded in the SREG bed, but further heat transfer to the EG portion of the bed is impeded, and hence the heat accumulation that occurs in the guideways leads to higher magnitude of the thermal error. The experimentally validated numerical model is used to extend the investigations to study the effect of the idle running of the longitudinal feed drive (LF) and combined cross and longitudinal feed drives, on the thermal behaviour of the lathe.
Present manufacturing trend is towards producing precision components with better accuracy. Machine errors like geometrical, thermal and process errors affect the component accuracy. Among these ...errors, thermal error contributes more than 50-60% of the total machining error. This paper mainly focuses on the development of a real-time thermal error compensation module for precision machine tools and talks about effective modeling of thermal errors, development of thermal error compensation model using feed-forward backpropagation neural network and also simplified model using regression analysis technique, algorithm development for real-time compensation and implementation of module onto the open architecture CNC controller. The developed module has been successfully tested on a Diamond Turning Machine (DTM) by machining the precision component and also verified the effectiveness of the module
Referring to the error modeling technology used in precision machine tools, it is difficult for machine tool builders to understand the effects of the theoretical modeling accuracy on the precision ...machining in the designing stages, where error components are represented by parameters. Therefore, this study is proposed to overcome certain theoretical calculation errors for a parametric form of volumetric error modeling and to examine verification method for judging the modeling precision. Based on the mathematical theory, a novel optimized algorithm is presented, as well as its verification methods. With the two new methods, it is effective to identify theoretical calculation errors and verify the accuracy of error modeling. Meanwhile, the proposed algorithm, with a form grinding machine tool being as an illustration example, is tested and validated by means of numerical simulations in the Matlab. The results reveal that the modeling accuracy of the error characteristic matrix is improved and enhanced by the algorithm, and the two verification methods can check the veracity of parametric modeling precision in different ways. Especially, the second method can check and isolate quantitatively the theoretical calculation errors. At the same time, it is a theoretical guidance for choosing a suitable treatment to meet the accuracy of an error model represented by parametric variables during iterations of the characteristic matrices. These two prediction veracity and uncertainty of the modeling precision can be evaluated. Furthermore, the algorithm and checking methods can be extended to ultra-precision multi-axis machine tools.
The high geometric accuracy requirement of precision machine tools represents a challenge for tolerance design and assembly process planning that guarantee the final assembly accuracy. Component ...tolerances should be allocated in association with assembly processes. However, tolerance design and assembly process planning are usually considered separately and lack quantitative analysis. In this paper, to integrate the geometric tolerance of components and variation propagation in assembly process, a state space model is developed. The measurement and adjustment process are expressed as observation matrix and control inputs. An optimal control problem is formulated to determine the adjustment process in consideration of the loss of final assembly accuracy and costs of remachining adjustment process. Tolerances of components can be optimally allocated based on the variation propagation in this deterministic assembly process. The generality and effectiveness of this approach are validated by applying the model on a four-axis horizontal machining center.
This paper proposes a novel comprehensive modeling method for deformation errors of different types of rolling joints in machine tools to improving the analysis efficiency. This method ...comprehensively considers the deformation of three types of rolling joints, i.e., linear guideway, ball screw and bearing, firstly from the perspective of analytical modeling. Two comprehensive models for deformation errors of all rolling joints in two types of motion systems of machine tools are established respectively with the method. The nonlinear interfacial characteristics at rolling joints and the geometric and stiffness coupling characteristics are considered. In order to study characteristics of the synthetical deformation error of rolling joints, a synthetical error model for a five-axis machine tool is developed. Several results and optimizations of the joints are carried out. The proposed method in this paper can effectively avoid the tedious finite element modeling in the traditional analysis process and improve the efficiency.
Based on the hardness inspiration of the tortoise structure, this study analyzes the innovative application of the parts of ultra-precision machine tools. Aiming at the problems of machining ...accuracy, efficiency, and machine cost of ultra-precision machine tools, an innovative design and analysis of chuck of ultra-precision machine tools based on carbon fiber-reinforced polymer and its application to turtle shell structure is proposed. Firstly, the G-element model of carbon fiber composites is deduced and analyzed by layered experiments. Secondly, the original parts of ultra-precision machine tool are simulated and analyzed, and the main sixth-order modal of carbon fiber turtle shell structure is deduced. Finally, the structural parameters of carbon fiber composite “turtle shell” were applied to the surface of chuck claw of ultra-precision machine tool, and the results were compared and analyzed. The results show that the maximum displacements of the chuck are all located at the front of the chuck and the maximum displacements and stresses of the chuck are smaller than those of the original chuck. The maximum stress is the most obvious, the difference is about 240.27 MPa, and the first-order mode increases by 23.4% compared with the original mode. The overall relative mass was reduced by 61.2%.
A v-groove structure is extensively used for planar optical-fiber alignment because of its unique features. To obtain low connection loss, the core pitch tolerance of a v-groove structure should be ...within submicrons. The squareness errors have great influences on the machining precision of micro v-grooves. Therefore, the actuarial calculation of squareness errors is of great significance for ultra-precision micro v-groove machine tools. In view of the disadvantages of the squareness error analysis method basing on small angle error assumption, the actuarial calculation of squareness error is implemented. A more precise geometric error model basing on the actuarial calculation of squareness error is established. The transformation between actuarial calculation of squareness error and improvement of machining precision is achieved through the geometric error modeling. The results show that the actuarial calculation of squareness error is effective and practical.
The positioning error of ultra-precision machine tools is the primary factor directly affecting the machining accuracy. It mainly depends on the machine tools guide. And its variation trend contains ...the same inertia as that of the machine tools movement. The variation trend of the positioning error is the derivative of a function fitted with the positioning errors of three adjacent testing points. The variation trends function is fitted with the variation trend of many points. The model of positioning error is the integral of the variation trends function. Because the variation trend of positioning error has certain inertia, the model of positioning error which is obtained in this way is more precise and more reliable than error function model which is directly fitted with limited discrete data.
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