Variations in running conditions cause fluctuation in the temperature field of precision machine tools, which inevitably results in thermal errors. To meet the demands of dynamic and time-varying ...temperature control capability, an active temperature control (ATC) method based on time grating principle is proposed, and the ATC system is developed. The ATC system contains main-loop and sub-loops. The oil target temperature in the sub-loop is determined according to the running parameters and the matching principle of the generalized heat generation–dissipation power. In accordance with the time grating principle, dynamic and differential oil temperature control of each sub-loop is achieved via the inlet time regulation of high-temperature (H-t) or low-temperature (L-t) oil in the main-loop. The main-loop H-t and L-t oil target temperatures are determined by the target range of the sub-loop temperature. The dynamic distribution of the refrigeration capacity and proportional heating mode is adopted to control the temperatures of H-t and L-t oil. By focusing on the feed system of precision machine tool, we carry out both dynamic simulation study and verification experiments, and the results show that the ATC method and system can effectively regulate the temperature field of precision machine tools, thus improving the thermal accuracy of the precision machine tool.
This paper studies the effect of stiffness (including slider stiffness and bearing stiffness) on the repeatability of the positioning of linear axes. First, a mathematical model between stiffness and ...the repeatability of the positioning of linear axes is established. The effects of the stiffness of the slider and bearing on the repeatability of positioning are analysed. The theoretical results show that the repeatability of the positioning decreases as the slider component stiffness and bearing stiffness increases. Second, a finite element analysis is implemented to calculate the effect of slider stiffness on the repeatability of positioning, the simulation results are found to be consistent with the theoretical results. Finally, the effect of bearing stiffness on the repeatability of positioning is experimentally investigated. The experimental and theoretical analysis results have been observed to coincide. Thus, the accuracy of the theoretical analysis is verified by both simulation and experimental results. The derived results afford designers and engineers a scientific basis for the stiffness design theory.
Volumetric accuracy is susceptible to thermal gradient caused by internal heat source (IHS) and external heat source (EHS). A temperature-structure multi-step calculation method is presented to ...investigate the influences of EHSs on volumetric thermal errors of precision machine tools. The temperature and structure of the machine tool are simulated first, and then, the volumetric thermal errors are calculated using multi-body theory method. Simulations are completed to study the effects of different EHSs on a machine tool, and series of validating experiments are carried out to verify the modeling method. The test results in specific position and working condition revealed that EHSs contribute 53, 21, and 68% of thermal deviations in X, Y, and Z directions individually. It is illustrated that the EHS is an important factor affecting the volumetric accuracy of precision machine tools. The methods provided in this paper are valuable for machine tool designers to evaluate the EHS effects on volumetric thermal errors during designing process; furthermore, some insulating measures are suggested to improve the accuracy and accuracy stability of precision machine tools by reducing the EHS influences.
In the present research, a method to model the pose error of the machine tool feed system is proposed based on the principle of minimum potential energy. Firstly, the force-moment equilibrium ...equation of the feed system is established by mechanical analysis. Secondly, the force of the single slider is analyzed based on Hertzian contact theory, and the force state of the slider under the action of the guideway error is obtained. The elastic displacements of the single slider in the horizontal and vertical directions are solved based on the principle of the minimal potential energy. Subsequently, the pose error of the feeding system is obtained by using the plane fitting principle. Finally, the correctness of the proposed method is verified through experiments, and the experimental results are in good agreement with the theoretical results.
Ultra-precision machine tool is the most important physical tool to machining the workpiece with the frequency domain error requirement, in the design process of which the dynamic accuracy design ...(DAD) is indispensable and the related research is rarely available. In light of above reasons, a DAD method of ultra-precision machine tool is proposed in this paper, which is based on the frequency domain error allocation. The basic procedure and enabling knowledge of the DAD method is introduced. The application case of DAD method in the ultra-precision flycutting machine tool for KDP crystal machining is described to show the procedure detailedly. In this case, the KDP workpiece surface has the requirements in four different spatial frequency bands, and the emphasis for this study is put on the middle-frequency band with the PSD specifications. The results of the application case basically show the feasibility of the proposed DAD method. The DAD method of ultra-precision machine tool can effectively minimize the technical risk and improve the machining reliability of the designed machine tool. This paper will play an important role in the design and manufacture of new ultra-precision machine tool.
An on-machine measurement (OMM) system is an effective apparatus for achieving an efficient profile compensation and improving machining conditions in ultrahigh precision machining. Herein, we report ...a new OMM system with a confocal chromatic probe on a five-axis ultrahigh precision machine tool constructed using a real-time position capturing method. The probe and machine tool positions are captured synchronously using a personal computer to generate profile measurement data. Long- and short-term stability, micro step response, and repeatability tests using an optical flat indicates that the system has a precision of approximately ±10 nm. The profile measurement test using a reference sphere indicates that the precision of the OMM system deteriorated at a large slope angle of ±45°. However, the overall accuracy is estimated to be within ±100 nm at a slope angle within ±15°. The linearity test at various slope angles indicates that the decrease in reflected light from a mirror-like surface deteriorates the performance of the probe.
A new thermal error control method based on the thermal deformation balance principle is suggested to control the thermal error of a precision machine tool’s functional parts, which negatively ...affects processing precision. The compensation of the thermal expansion of metal by the thermal contraction of carbon fiber reinforced plastics (CFRPs), which has a negative linear expansion coefficient, lies behind this method. The metal structure is bonded with CFRP bandage and thermoelectric modules to achieve the temperature difference between the metal and the CFRP, thereby realizing the same thermal deformation. The heat transfer channel in the compensation system for thermal deformation is designed by the structural topology design method to distribute the heat evenly. Experimental and numerical simulation results show that the suggested approach reduces thermal displacement by 93% compared with the metal structure without the CFRP bandage. The suggested method can be applied to thermal deformation compensation for various high-precision equipment, including coordinate measuring machines, aerospace equipment, and optics and optical instruments.
•The rotational speed control system of the water-driven spindle was designed in the present paper.•The designed feedback control system can reduce the change in the spindle speed due to the cutting ...forces.•The disturbance observer was added into the feedback control system.•The influence of cutting force on spindle speed can be minimized the designed control system with disturbance observer.
The water driven spindle has been developed for use in an ultra-precision machine tool for producing precision parts. In order to achieve high machining accuracy and generate high-quality surfaces, precise rotational accuracy and a constant machine tool spindle speed are necessary in ultra-precision machine tools. However, the rotational speed of the spindle inevitably changes due to the influence of the cutting forces during machining process. In order to deal this problem, this paper describes the development of a rotational speed control system. In particular, the control system is designed such that the influence of the cutting forces is effectively reduced. In this paper, mathematical models of the water-driven spindle and the flow control valve are introduced to develop a feedback control system. The effectiveness of the developed feedback control system is then verified through simulation and experimental tests. In addition, the disturbance observer is added to the designed feedback control system in order to minimize the influence of the cutting forces. Turning tests are then carried out in order to verify the effectiveness of the disturbance observer. As a results, the developed feedback control system with the disturbance observer is verified to successfully reduce the change in the rotational speed.
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