Research On The Key Technique Of Flexible Articulated Arm Coordinate Measuring System

With the rapid development of advanced manufacture technology, reverse engineering as an advanced technical means to get three-dimensional model of the objects has been widely applied in the field of large parts and components inspection, quality control and virtual reality. Coordinate measuring machine is the traditional Cartesian measurement equipment, and it is called as "Measurement Center" with its mature technology and its superior performance. Due to the constraint of three mutual perpendicular railways and installation environment. It is difficult to meet a variety of on-site measurement requirements in the industry. As a new type of multiple degree of freedom and non-Cartesian coordinate measuring machine, flexible articulated coordinate measuring arm realizes its measuring function via angle measurement, not length measurement. It has vast application and potential prospect, as it possesses the advantages of portability, compact volume, large work range, flexible movement and low price, moreover convenient to on-site measurement.The major issue comprises mechanical structure, data acquisition system, kinematic model, error analysis and calibration technology. The dissertation systematically and deeply discusses these issues through theory and technology levels.For the characteristics of the flexible articulated coordinate measuring arm, the mechanical structure and data acquisition system are dexterously designed. To ensure the accuracy and compactness of this measurement equipment, rotation components adopt high-precision bearings and are insured their body to reduce shaking by all means. Slip rings are utilized to realize the purpose of unlimited rotation, so as to avoid the signal line within the measuring arm to break down. Data acquisition system adopts the advanced embedded systems and field bus technology, to reduce the number of signal transmission lines, debase the complexity of the mechanical structure and improve stability and reliability of the data acquisition system.According to a great deal of literatures, it is proved that the 95% measurement error are caused by the inaccurate kinematic model. Thus, a right kinematic model is extremely important to a measuring arm. Most institutions or scholars at home and abroad still adopt the traditional D-H model as the kinematic model of the measuring arm. But its shortcoming is that it lackes completeness as a 4 degrees of freedom parameter model. Therefore, this study proposes the principle of establishing benchmark gesture so that it is convenient to set up the kinematics model of a measuring arm via the product-of-exponentials formula and the local product-of-exponentials formula. Because the two models are the model of 6 degrees of freedom parameter, they can overcome the shortcomings of the traditional D-H model. Based on the established kinematic model, the principle of the key pole length is proposed to avoid the cavum phenomena in the measurement range.Based on the three aforementioned models, error sources of the measuring arm are analysed, the kinematic correction models are established and the influence of each error of the kinematic parameters on measurement precision is detailedly studied, in order to provide a theoretical basis for the design and manufacture of the measuring arm.In order to improve the measurement precision of the measuring arm, two novel calibration methods for measuring arm are presented. The advantages of two calibration methods simplifies calibration process and are easy to implement. Compared to the traditional methods, they overcome some shortcomings such as complicated algorithm, matrix ill condition, initial value sensitive, computational error caused by reverse and differential calculation and the obtainment of the local optimization without the global optimization. Calibration results show that measurement precision after calibration meets the precision requirement of the measuring arm.These studies constitute a set of key technologies for flexible articulated coordinate measuring arm, and provide favorable theoretical foundation and technical support for developing a measuring arm. In addition, some key technologies of non-contact laser scanner are analyzed, summarized and exploringly studied to accumulate forward-looking technological reserve for integrating laser scanner into the measuring arm.