Study On Mechanical Structure And Measuring Error Of Artificial Coordinate Measuring Machine

The Articulated Coordinate Measuring Machine is a new type of non-Cartesian CMM, which can be used in many fields such as Reverse Engineering and industrial local measuring. Compared to the conventional coordinate measuring machine, the A-CMM is lighter, compacter and portable CMM, and It has more freedoms, which assure it is agile when being used on coordinate measuring. But on the other side, It has some shortcomings; because measuring errors resulted by angle errors will be remarkably magnified by length of links and measuring errors of will be added, the measuring accuracy of A-CMM is quite low, which account for the importance to elevate the measuring accuracy of it. About this problem, several aspects of research are carried in this dissertation. On mechanical design of the links and joints, the countermeasures to low measuring accuracy of A-CMM include: making the links by carbon fibre to minish the effect of fluctuant environmental temperature on measuring accuracy, using two angular contact ball bearing to form a back-to-back duplex bearing at every joint to reduce deviation of joint axis and measuring error. After fixing coordinate system of each joint, Measuring Kinematical Equation and Measuring Error Equation are established according to the principle of spatial homogeneous transformation. On this base, three methods for the calibration of the structural parameters of the instrument are put forward in this paper, and After these methods being compared, a scheme for calibration is brought forward, which synthesizes their strongpoint. To achieve higher measuring accuracy of the apparatus, this dissertation presents a new idea that quantitative analysis and research on the measuring error resulted by deviation of joint axis should be carried out; On the base of the former Measuring Kinematical Equation, the deviation of joint axis is taken into consideration and the matrices represented it are added into the equation, and then the modified Measuring Kinematical Equation is founded. The difference of two equations is just Measuring Error Equation resulted by the deviation of joint axis. Through the idea that assuming the whole apparatus as three independent parts, the maximum values of this kind of Measuring Errors are worked out by this equation.