Papers by Author: Shu Gui Liu

Abstract: Compared to the conventional CMM(coordinate measuring machine) with three orthogonal axes, the CCMM(Cantilever CMM) researched in this paper has two axes perpendicular to each other and one rotary axis. Hence, the error parameters in CCMM are also different from the 21 items geometrical errors in CMM. The application of REVO in CCMM makes a big difference compared with the application in CMM. This paper analyzes the error items existed and needed to be calibrated in CCMM and identifies the error parameters of REVO schematically, which lays a solid foundation for further research and application of REVO in non-orthogonal CMM.

Abstract: A wireless control system for pointolite on the light pen based on TMS320DM642 and CC2530 is introduced in this paper, in order to solve the problem that only pointolite's switch values could be controlled on the light pen in light-pen CMMs, but not lightening time values and brightness values. Through wireless networks of Zigbee, not only pointolite could be switched on or off separately, but also lightening time values and brightness values could be changed by TMS320DM642. Protocols of wired and wireless communication, multipoint answer and error reporting are also given, to improve anti-jamming capability of the system. The experimental result demonstrates that the control success rate could reach 96%, as the wireless modules of TMS320DM642 and the light pen within 8m. So the developed system has high anti-interference capability and could meet expected requirements.

Abstract: Cantilever CMM(short for coordinate measuring machine) is non-orthogonal type one with large measurement range, small volume, light weight, low cost, but lower precision. Error calibration and compensation is an important way to improve the measurement accuracy . This paper presents a new calibration method for the length of articulated arm just using the square. Facility requirement is relatively low and it is easy to operate. Comparing with that measured by laser interferometer, this method has a relatively high accuracy, having a certain value in practical measurement.

Abstract: As an important part of the aero engine, the quality of the blade seriously affects the engine performance, so the inspection method of the blade is significant. Based on the research of the HB 5647-98<<to mark dimensions, tolerances of the vane type and the surface roughness of the blade body>> , this paper concludes different evaluation methods of the blade. The main evaluated parameters include the leading and trailing edge radius, the chord length, the maximum thickness of blade profile, the mean camber line, and the surface twist and so on. Here we mainly discuss the previous three terms. The least square method is adopted to fit the arc of the leading and trailing edge; introduce the projection method to calculate the chord length; at last, we employ the spline fitting method to get the mean line and then obtain the maximum thickness of the blade section.

Abstract: The paper proposes a novel method of improving the traditional composite grating in 3-D measurement of the specular objects. The traditional composite grating is improved by altering the intensity of the center stripe in one of the fringes. The improved composite grating not only includes the primary phase information, which is modulated by the object's surface, but also includes the code information, which is necessary for the phase unwrapping. The paper introduces the formation of the improved composite grating, demodulating the composite grating and computing the unwrapped phase based on the altered fringe. Simulated and actual experiments prove that this method is valid. Because of projecting a single composite grating, the method is suitable for dynamical measurement.

Abstract: A new 5-DOF flexible coordinate measuring machine (CMM) is introduced in this paper, which uses REVO system produced by Renishaw. According to the D-H method, the mathematical model is built, and then the error model of the flexible CMM is derived. The parameter calibration based on the nonlinear least square method is analyzed theoretically. Due to the disadvantages of Gauss-Newton method, LM method is researched, which improved the singularity of the coefficient matrix. The calibration analysis is a basis for improving accuracy of the flexible CMM.

Abstract: A new type of coordinate measuring arm with a Revo revolving body which can realize quick measuring in spherical domain has high stability, fast measuring speed and high accuracy compared with common coordinate measuring arm. We use the method of space coordinate transformation to solve the problem that the transformation matrix can’t be got from Revo body to test head by DH method, and apply DH theory to build the mathematical model of system. The system model is verified right by sketching. The error model is built and the effect of measurement accuracy from all error sources is deeply analyzed. It presents a theory foundation for further researching on improving accuracy of this new type of coordinate measuring arm.

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.