一种过定位下工件定位误差的计算

提出了计算“4-2-1”过定位下工件定位误差的方法,考虑了两个条件：一是定位件与工件不发生干涉,二是保证工件放置的稳定性。根据以上两个条件,把“4-2-1”过定位下工件定位误差的计算分为五个具体的步骤,最后举例说明了本方法的实用性。     

Steady state errors transferred to the turned workpiece

Even if tool and workpiece are set correctly, several errors transfer to the turned workpiece owing to the inherent sources of inaccuracy of the processing system. An evaluation of such errors showed that they partially transfer to the turned workpiece. The ratio of transferred to introduced errors depends upon the ratio of the tangential to the radial compliance of the system.     

Selection of preliminary locating and clamping positions on a workpiece for an automatic fixture design system

This paper focuses on the development of heuristic algorithms for selecting the locating and clamping positions on an automatic fixture configuration for a given workpiece for an automatic fixture design (AFD) system. It discusses several issues regarding (i) an informationally complete product model, and (ii) the development of necessary computational modules coupled with a knowledge based system to reason about the workpiece's geometric characteristics for determining the locating and clamping positions. The motivation of the work is to develop a fixturing subsystem as an integral part of the complete CIM environment. A prototype AFD system has been completed in the object oriented programming platform of Wisdom's Concept Modeller. It has used several geometric reasoning mechanisms based on the traditional fixture design principles, and on the principles of collision-free assembly. The system exploits the power of Wisdom's advanced geometric modelling (AGM), and it implements the basic architecture of the proposed knowledge based fixture design system.     

Roughness due to workpiece wear generated in surface grinding of metals

Assuming the grinding wheel surface to be fractal in nature the maximum envelope profile of the wheel and contact deflections are estimated over a range of length scales. This gives an estimate of the ‘no wear' roughness of a surface ground material. Four test materials, aluminium, copper, titanium and steel are surface ground and their surface power spectra estimated. The departure of this power spectra from the ‘no wear' estimates is studied in terms of the traction induced wear damage of the surfaces.     

接触变形对工件加工误差的影响

基于工件的准静态受力分析 ,运用经典Hertz接触理论 ,计算夹具 工件接触区的变形。根据多刚体运动学 ,建立表面加工误差和接触变形的关系 ,对加工误差进行预报。此方法也可用来计算定位基准误差对加工误差的影响。     

Self-calibration and compensation of setting errors for surface profile measurement of a microstructured roll workpiece

Microstructured roll workpieces have been widely used as functional components in the precision industries. Current researches on quality control have focused on surface profile measurement of microstructured roll workpieces, and types of measurement systems and measurement methods have been developed. However, low measurement efficiency and low measurement accuracy caused by setting errors are the common disadvantages for surface profile measurement of microstructured roll workpieces. In order to shorten the measurement time and enhance the measurement accuracy, a method for self-calibration and compensation of setting errors is proposed for surface profile measurement of microstructured roll workpieces. A measurement system is constructed for the measurement, in which a precision spindle is employed to rotate the roll workpiece and an air-bearing displacement sensor with a micro-stylus probe is employed to scan the microstructured surface of the roll workpiece. The resolution of the displacement sensor is 0.14 nm and that of the rotary encoder of the spindle was 0.15r~. Geometrical and mathematical models are established for analyzing the influences of the setting errors of the roll workpiece and the displacement sensor with respect to the axis of the spindle, including the eccentric error of the roll workpiece, the offset error of the sensor axis and the zero point error of the sensor output. Measurement experiments are carded out on a roll workpiece on which periodic microstructures are a period of 133 i~m along the circumferential direction. Experimental results demonstrate the feasibility of the self-compensation method. The proposed method can be used to detect and compensate the setting errors without using any additional accurate artifact.     

Temperature distribution in the workpiece due to plane magnetic abrasive finishing using FEM

A mathematical model is developed for the prediction of magnetic potential using Maxwell’s equations and finite element method is used to find the magnetic potential distribution within the gap between tool bottom surface and workpiece top surface. From magnetic potential model, the magnetic pressure developed and corresponding heat flux generated on workpiece surface are evaluated. Further a mathematical model is developed for heat transfer in the workpiece and again finite element method is used for the prediction of temperature rise in the workpiece. The effects of various operating input parameter on magnetic potential distribution in the gap and temperature rise in the workpiece has been studied.     

Three-axis correction of distortion due to positional drift in scanning probe microscopy

Two common sources of distortion in scanning probe microscopy are piezo creep and thermal drift, the latter caused by slow thermal expansions of materials in the sample and microscope due to small changes in temperature over the course of a scan. We present a technique for correcting distortion due to thermal drift along all three spatial axes, along with simultaneous correction of z-axis piezo creep. Our method works by comparing each scanned topographical image to a second, partial scan, taken immediately afterwards, on which the fast and slow scan axes have been reversed. We model the positional distortion as a low-order polynomial function in three dimensions, searching for the set of correctional coefficients that minimizes the root-mean-square difference between the two scans. We demonstrate in a variety of real-world and simulated tests that this technique can routinely reduce distortion from these effects by over 90%, often to a precision of better than a single pixel.     

NC simulation with dynamic errors due to high-speed motion

Traditional NC simulation has not always considered dynamic contouring errors in machining when simulating a tool path. For instance, if the feed rate is high, the effect of dynamic machining errors will be apparent on the work piece, but traditional NC simulation does not account for the dynamic errors at all. Due to the increasing demand of reducing product cycle time, high-speed machining of dies and moulds are becoming more and more popular. Under high-speed motion, over-cut or gouging can easily occur even when traditional NC simulation proves that the NC path is correct. Therefore, it is of significance to be able to predict dynamic machining errors in NC simulation before the part is machined, especially under high-speed motion. This paper presents the simulation of NC machining with dynamic contouring errors under high-speed motion. By adding dynamic error models to a simulation, the errors can be clearly displayed on a Z-map model. Hence, it becomes possible to predict under what conditions dynamic errors may occur. Comparing the Z-map model after simulation with the CAD model also makes it possible to find where the dynamic errors occur. This will also allow us to obtain useful information to determine where and when to change the feed rate in order to meet the accuracy requirement.     

虚拟数控车床螺纹加工中的工件建模方法

工件建模方法是虚拟数控加工中的关键技术,由于其形体在加工过程中不断变化,所以其模型需要能够根据加工过程实时调整.在介绍传统数控车床虚拟仿真系统的工件建模方法的基础上,分析了其在螺纹加工过程中的不足,并给出了适合螺纹加工的工件体建模方法,并使用OpenGL和VC++编程实现了螺纹体的建模.     

Modeling and analysis of workpiece stability based on the linear programming method

After being located on a machine bed, a workpiece will be subject to gravity and cutting forces during the machining operation. In order to keep the locating precision as well as the production safety, it is necessary to maintain the workpiece stability. In this paper, a linear programming method is proposed for stability analysis of the workpiece. Based on the linear approximation of the friction cone, a quantitative criterion is established to verify the workpiece stability in association with the rationality of the clamping sequence, magnitude of clamping forces and clamping placement. This criterion allows designers to plan reasonably the clamping sequence, magnitude of clamping forces as well as clamping placement. Compared with existing methods, the main advantage of this approach lies in that the sophisticated computing of contact forces between fixture elements and the workpiece is avoided. In this work, both friction and frictionless cases can be easily taken into account in stability analysis. Mathematical formulations of the method are given and some numerical tests are finally demonstrated to validate the proposed method.     

Correction of autofocusing errors due to specimen tilt for automated electron tomography

Transmission electron microscopy images acquired under tilted‐beam conditions experience an image shift as a function of defocus settings – a fact that is exploited as a method for defocus determination in most of the automated tomography data collection systems. Although the method was shown to be highly accurate for a large variety of specimens, we point out that in its original design it can strictly only be applied to images of untilted samples. The application to tilted samples and thus in automated electron tomography is impaired mainly due to a defocus change across the images, resulting in reduced accuracy. In this communication we present a method that can be used to improve the accuracy of the basic autofocusing procedures currently used in systems for automated electron tomography.     

一种波纹喇叭零件的加工

通过对深腔波纹喇叭零件的结构和加工工艺分析,提出了采用不同直径的钻头首先将内腔粗钻成台阶孔,然后使用专门设计的镗刀完成内腔的精加工,最后使用专门设计的切槽刀粗精车各环形槽。实现了零件的数控加工,解决了深锥孔以及内环形槽的加工难题。     

Prediction of dimensional errors in 3D complex shapes due to press elasticity

This paper presents an approach to predict dimensional errors in 3D complex shapes due to press geometry errors and elasticity. Using a press stiffness matrix formulation for the press deflections in forging operation, a quantitative relationship between forging die deviations and the press geometry errors and elastic deflections is developed, which is a function of the forging force, press stiffness and the spatial relationship between the forging dies and the press table. The stiffness matrix of a screw press is obtained using finite element analysis. To evaluate the effect of the press elasticity on dimensional errors of 3D components, a case study of forging for aerofoil shapes is carried out based on the results from physical modelling experiments. With the representative information of the tool shape and forging force data, numerical results of the forging die deviations as a source of dimensional errors for the aerofoil shape are obtained and evaluated. It is demonstrated that this approach is applicable to forging and other metal forming processes for complex shapes.     

A review of the theory of Coriolis flowmeter measurement errors due to entrained particles

Coriolis flowmeters operate with high accuracy when the medium metered is a single-phase incompressible fluid. Multi-phase fluids lead to measurement errors because of center-of-mass motion. In this paper we review the “bubble theory” which describes errors due to phase decoupling of two-phase fluids. Examples are provided with combined phase decoupling and compressibility errors.     

Cup anemometer measurement errors due to problems in the output signal generator system

The effect of drops in the rotation wheel of the opto-electronic system of a commercial anemometer (Thies First Class Advanced) was studied. The output voltage of this anemometer was measured at different wind speeds during its calibration process, at 25 kHz sampling frequency along 25 s. The output frequency was calculated both ways: by counting pulses (CP) and by carrying out a Fast Fourier Transform (FFT). The errors of the anemometers transfer function based on both procedures are given in relation to the official (MEASNET) calibration. The effect of the sampling frequency is also analyzed together with the presence of oil drops. No effect of the oil drops was observed on calibrations carried out by extracting the anemometers transfer function with FFT. When using CP, results showed great differences between calibrations affected and not affected by the presence of oil drops in the rotation wheel of the opto-electronic system.     

Reconstruction of geometry information to gasbag polishing workpiece

In order to solve the problems of reconstruct an unknown workpiece operations are always required by CAD information of workpiece which cause eeficiency low, operation complex and so on, the one which design and implementation of gasbag polishing operations which can automatically online reconstruct the geometry information of workpiece was investigated. The operation method of online reconstruction of a workpiece surface and the basic theory were introduced, in order to obtain the normal vector of workpiece surface. The outer ring of active compliance control based on the inner position loop was proposed, the position compensation at the end of the polishing manipulator was used to achieve the gasbag polishing contact force control. The contact force model of gasbag polishing was established. The trajectory planning algorithm with time-varying constraints was established. An experimental platform which is capable to reconstruct an unknown workpiece was built, the theory was simulated. The results indicate that this strategy is feasible and rffective. [ABSTRACT FROM AUTHOR]     

Study on the influence of geometric errors in rotary axes on cubic-machining test considering the workpiece coordinate system

Evaluating the influence of geometric errors in rotary axes is a common method used by a five-axis machine tool for improving the machining accuracy. In conventional geometric error models, the table coordinate system is considered as the final workpiece coordinate system. In this study, an additional workpiece coordinate transformation was proposed to identify the influence of geometric error. First, a cubic machining test was conducted. Second, the necessity of workpiece coordinate transformation was analyzed, and a method for coordinate transformation was proposed. In addition, both machining simulation and an actual machining experiment of the cubic machining test were conducted to verify the efficiency of the proposed method. The results indicate that the workpiece coordinate transformation is an essential part of the geometric error model for accurately simulating the geometric error influence. The method for identifying the geometric error influence considering the workpiece coordinate transformation is applicable in manufacturing.     

Theory of errors in Coriolis flowmeter readings due to compressibility of the fluid being metered

The compressibility of fluids in a Coriolis mass flowmeter can cause errors in the meter’s measurements of density and mass flow rate. These errors may be better described as errors due to the finite speed of sound in the fluid being metered, or due to the finite wavelength of sound at the operating frequency of the meter. In this paper, they are investigated theoretically and calculated to a first approximation (small degree of compressibility). The investigation is limited to straight beam-type (and does not consider shell-type) Coriolis meters. A lumped-parameter (coupled oscillator) model is used to explain the process causing the errors, and a simple 2-D continuum mechanics model is used to derive expressions for the magnitudes of the errors. Applications might be to Coriolis metering of gases, or to two-phase mixtures in the form of aerated liquids.     

Analysis and compensation of positional and deformation errors using integrated fixturing analysis in flexible machining parts

The final precision with which workpieces are formed strongly depends on good design and correct operation of fixtures. The main errors introduced by fixtures are related to positioning, indentation and structural deformation. This paper describes a procedure for studying these errors, which integrates positioning and deflecting fixturing analysis methods. These methods are applied to the special case of flexible workpieces, which are fixed by hyperstatical fixturing systems when the roughing and finishing operations are carried out in the same setup. Once these errors have been calculated by the integrating procedure, all the information is introduced in a CADCAM database so that the above errors can be compensated during the machining operation by means of a new cutting tool path provided by the CADCAM program.