Key Engineering Materials Vols. 381-382

Abstract: The dynamic characteristic of CNC (computer numerical control) machine tools is a critical role to decide the accuracy and speed of machine. It is very important to improve the precision and reduce the motion error so as to manufacture complex and fine products. In general, the motion error is estimated by a two or three-dimensional ball bar measurement system. Although this technology is capable of dynamical measurement, its condition should be confined to a low speed or a large radius. A new measurement method for measuring circular motion error of CNC machine tools is proposed in this paper. The instrument consists of a dual-frequency laser interferometer, a beam splitter and two corner cubes. In order to evaluate the exactness of the results we get from our measurement system, we use RSF’s grid encoder to do another experiment and compare both the results. According to the results shown, our measurement system can measure both of the X and Y axes of the plane of the CNC stage in a small scale at the same time and can simplify the calibration procedure as well as shorten the time of measurement. This method can accomplish the two-axis measurement at a high speed, without being restricted by radius variations. It is a good, simple and effective measurement method.

Abstract: An optical-electronic measurement system for continuous monitoring of displacements and analysis of the friction pendulum bearings for the oil-drilling platforms is presented. Measuring principle of the system is based on target image formation by camera and digital image processing. The passive part of the system (optical target) is fixed on one part of construction while active part - a field measurement sensor (FMS) - is installed on another part of construction that moves relative to the first one. On the FMS output, after processing, the relative displacement between FMS and optical target is obtained with high degree of accuracy. The spatial resolution of a few micrometers can be achieved at cost of reduced measurement range.

Abstract: A basic analytical model of the out-pump type complex journal gas bearing is set up to investigate the coupling mechanism between aerodynamics and aerostatics in a complex gas bearing and to improve its performance, under incompressible conditions. The analytical model shows that the load-carrying capacity function is composed of five items. Apparently, there is both pressure and structure coupling between aerodynamics and aerostatics; identically, the surface feature function is positive; and when the groove distribution coefficient is 0.30, it is approximately maximum.

Abstract: The thickness of water film is an important parameter in the field of chemical industry. Water film is formed by the flowing water, which flows through a narrow channel. So it is difficult to use contact gauges to measure the water film because it’s flowing so fast that if it is touched, the thickness will be changed. A low-cost and high precision non-contact measurement method—capacitive sensor is used as the sensor of the thickness of water film, virtual instrument is used to analyze the measurement state. In contrast to the conventional stand-alone instruments, a PC based virtual instrument for the measurement of water film is proposed in this paper. Based on on-line measurement theory, real time voltages should be collected to PC. These voltages will be computed by formulas in Labview and the real time data of thickness will be plotted on the screen. If bad signal got, it will give error alarm. The method of the measurement of water film can save a lot of fees of research and applications, and be easy to apply in other measurement and control fields. The basic principle and working process of capacitive micrometer, denoise method, the method of capacitive calibration, virtual instrument data acquisition system and on-line measurement of water film, will be further discussed in this paper.

Abstract: A simple and practical calibration method is proposed to calibrate the articulated arm flexible CMM. Firstly, a quasi-spherical coordinate system is put forward based on DH method according to the special structure of the articulated arm flexible CMM. This calibration method is presented to determine and separate machine parameters and errors in a creative way based on multiple reversal technology. Experiments were carried out for a Faro Platinum 4ft articulated arm CMM by using a Chameleon 9159 5Q orthogonal CMM. The results prove the feasibility of the proposed method for articulated arm CMM calibration, and all parameters are separated completely. It provides a theoretical base for introducing error compensation and improves the measurement accuracy of the articulated arm CMM.

Abstract: The theory of dynamic measuring accuracy is the important basic theory of dynamic measurement, guarantees the optimal working state of measuring system and measuring instrument, and is the basis of optimal economical effect of instrument design and manufacture. Because dynamic measuring accuracy theory involves many aspects of theory and technology, model-building of dynamic system, error model-building and design method of dynamic system accuracy are discussed in this paper.

Abstract: In this paper, the characteristics of the high temperature environment in tin bath and the practical glassmaking of float glass production are analyzed. Dynamic optical measuring method is selected to measure glass thickness. A semiconductor laser is used for the light source and a linear CCD is used for the detector to pick up data within 600°C on the area of the tin bath. By analyzing and calculating a lot of dynamic measurement experimental data tested with the measurement device. Based upon the theory of heat transfer, the working area of the measurement device can be kept at a constant temperature near the tin bath by using a circulation water-cooling system and low temperature nitrogen. The image processing technology is used for the edge detection and the pixel subdivision in the software of the system. At the same time the factors that influence accuracy of the system are discussed and some compensation measures are also proposed. The accuracy of 5µm dynamic on-line measurement is achieved and the accuracy of static measurement is less than 1µm within the range of 2~20mm thickness of glass. All these make linear CCD can be successfully applied in the practice of high temperature environment.

Abstract: A novel scanning probe measurement system has been developed to achieve precise profile measurements of micro-aspheric surfaces. The system consists of a scanning stage (a spindle and a linear slide) and a sensor unit. The sensor unit consists of a ring artifact, two capacitance sensors and a contact-mode displacement sensor. The two capacitance sensors scan the surface of the ring artifact to measure and compensate the error motions of the scanning stage while the contact-mode displacement sensor scans the surface of a micro-aspheric. In this paper, a new contact-mode displacement sensor that has a small contact force of less than 2.3 mN and a stable output has been developed. After investigating the fundamental performance of the contact-mode displacement sensor, the sensor has been applied to the micro-aspheric surface profile measurement system. The effectiveness of the measurement system has been verified by the measurement results.

Abstract: The object of this paper is to describe the process and current status of the development project of an Ultra Precision Gear Measuring Instrument that guarantees a measurement accuracy that falls into a submicron range. The angular indexing mechanism, which is the basis of its measurement accuracy, consists of a purely mechanical system. The system is based on the concept of accuracy feedback where its own deviation estimated from measurement results is fed back into the finishing process. It consists of basic axes with minimum error causing factors in order to seek the optimum accuracy that can be achieved by precision machinery. The measurement accuracy of this measuring instrument has already reached the submicron range in its initial assembly state.

Abstract: In order to allow optical signals to reach the workpiece surface to realize in-process optical measurement through an opaque coolant, a locally transparent region generated by use of an air beam is examined to allow better understanding of the fluid assisted in-process optical measurement approach. With the air beam used, the problems associated with the diluting effect on coolant concentration and the measurement error due to the optical transmittance through multiple media can be avoided. The working principle and the experimental results for testing the proposed method are presented and discussed.