| Coordinate Measuring Machine (CMM) is a flexible high precision apparatus by mechanism. Orthogonal coordinate system CMM is running on the orthogonal linear guide way mechanism and has visual and easy conversion advantages. But non-orthogonal coordinate system CMM uses other mechanism and is small and light, carried easily, so is being developed. With the development of heavy and high speed railway in China, there is need of measuring the profiles of wheel and rail with higher efficiency and precision, for research of the relation between wheel and rail, and monitoring of railroad running security, So the research of wheel's and rail's profile meters, based on non-orthogonal coordinate system CMM theory is very important.This research first reviews the devolopment course of classic CMM and the non-orthogonal coordinate system CMM with multi-joint serial mechanism, Based on the current research in parallel mechanism CMM and in wheel/rail profile measurement, this paper shows the author's theoretical and application research. The main topics, methods and results are as follows:1. The mathematical principle of coordinate measurement and realization of non-orthogonal coordinate system are summarized; the CMM system functions is decomposed and recomposed for optimization, the feasibility of non-orthogonal coordinate mechanism is proved. The measurability is studied by analyzing solving of the nonlinear equation for both multi-joint serial and parallel mechanisms; and mechanism's Jacob matrix and its condition number is discussed. All these work provide theoretical basic for mechanism design.2. The accuracy of the non-orthogonal coordinate system CMM is investigated. The calibration and compensation of manufacturing errors of mechanism are studied; measurement errors are analyzed by calculating simple thermal, stress deformation and joint angle errors, the analysis and experiments of multi-joint series mechanism indicate that it is possible to calibrate a angle zero position error by measuring identical profile with two different poses and making two results overlap, and it is possible to calibrate multiple errors bybreaking down calibration of single error in turn; the experiments of measuring profile errors with eddy and laser displacement sensors have been finished.3. The structure synthesis of non-orthogonal mechanism is investigated. Based on study of design approaches and mechanism factor, structure synthesis of planar measurement mechanism, two design plans are proposed: (DThe first one is a CMM based on measuring rod length of parallel mechanism and its mathematical model is determined, the forward and inverse solutions are calculated, the measurable space and measuring accuracy are analyzed. ?The second is based on measuring angle suites high speed measuring in small scope, with 3 or 6 degrees of freedom.4. The application of parallel mechanism in wheel/rail measurement is investigated. Three schemes of apparatus are proposed: ?portable wheel/rail profilometer based on angle measuring of five links mechanism, its structure is designed and measuring errors are analyzed, another scheme is given; (2) automatic measuring device for wheelset geometric parameters based on measuring and controlling links length of triangle is proposed; (Da handcart measuring railroad track gauge and cross level based on measuring angles, a novel eddy damping structure is applied in the inclinometer, measurement models are derived.5. The data acquisition in CMM and mechanism motion control is investigated. The realization technology is discussed about four subdivides of grating signal, reversible counting function, and precision subdivides of sine signal. Portable data acquisition device is designed with F2407 as CPU, and its power consumption, the USB connection and its two sides programming, hardware connection, angle zero determination, high speed synchronous locking and readout the counter values, and wireless communication are investigated.6. An automatic scan scheme for free surface curves of iron workpiece cross-section is proposed. The measuring mechanism can control and measure an encoder's planar position and an end of measurement rod is fixed on shaft of the encoder and another end with magnetic measurement wheel. The strategy is that using rod's gravitational effect and swing angle to automatic search object then adjust the measuring rod direction and go forward one step, by last measured two points' position. The experiment indicates this method is simple, economical, andadaptive to different positions and cross sections of work pieces.This research work has some main innovation: it is the first time to thoroughly study the principle, method, measurability and accuracy of coordinate measuring machine based on non-orthogonal coordinate system. Considering the characteristic of coordinate measurement, the structure synthesis of measurement mechanism is investigated, and four novel apparatuses or its plan are proposed:(l)The first one is a plan of CMM based on measuring length of rod, can realize high accuracy of measurement with simple manufacture process. This plan has been patented as a Chinese Invention Patent ZL011128866.3.(2) A six degrees of freedom parallel mechanism based on angle measuring can be applied to measure dynamic postures of the brush pen so that it makes digital long history calligraphy.(3) A plan of planar coordinate measuring mechanism with five links based on measuring angle can be used to make portable profilometer for measuring various of wheel/rail profile, integration of wheel/rail geometry instruments and higher accuracy of measurement can been realized(4) An automatic measuring device for wheelset geometric parameters based on measuring and controlling links length is developed, based on its coordinate measuring adaptive function, wheelset lift and position devices are removed then make it simpler. This plan has been patented as a Chinese Invention Patent ZL01108526.6.
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