Executive Summary : | Objective: The demand for high precision components with dimensions in the micro to meso scale range is continuously increasing as dictated by the increasing living standard of human beings longing for high level smart phones, minimally invasive medical equipment, miniaturized digital cameras, micro-turbines, micro-nozzles, optical equipment etc., all of which possess complex 3-dimensional geometries. With the invention of ultraprecision machine tools or reconfigurable micro-factories and various additive or subtractive micro-manufacturing technologies, the availability of manufactured microparts in the market is increasing. However, the demands for ever-tighter tolerances on dimensions, forms and surface finish are placing a considerable pressure on current technological limits. One of the main barriers is the limited accuracy of manufacturing and verification machines and systems. To alleviate this problem, two developments are proposed in this work: 1) Development of a unique 3D parallel-architecture ultra precision CMM, and 2) Formulation and development of calibration and real-time volumetric error compensation methodology, algorithms to achieve sub-micron range accuracy. Summary: This proposal mainly focuses on the development of ultra-precision co-ordinate measuring machine with sub- micron accuracy to overcome the main barriers of limited accuracy of existing inspection machines and systems. There are 11 types of high precision CMMs available in form of lab prototypes or commercial machines within which 7 CMMs have serial kinematic based translational stage/ moving probe and 4 micro-CMMs have parallel kinematic stage. However, in parallel kinematics high load/ weight ratio, higher stiffness, higher accuracy and lower inertia can be realized. But complex forward kinematics, small workspace and complicated structures are mainconstraints to achieve parallel kinematics translational stages in CMMs. Therefore, a target is to be set to minimize these complicacies in parallel kinematic stage to achieve higher accuracy. On the other hand, if the probe is moving during the measurement, the measurement error will be more due to instability of the probe. Only 4 developed micro-CMMs have the facility for static probe. Also most of these micro- CMMs have very large foot print, which can increase errors due to large structure. Another main design consideration to achieve ultra- precision CMM is to obey the Abbe principle for all three degrees of freedom (in X-, Y- and Z- directions). However, no developed CMM have the facility to avoid Abbe errors for all of the 3 axes. Also, in all the above- mentioned developments the system’s accuracy mainly relies on the manufacturing and assembly tolerances. None of these systems uses real-time error compensation techniques, which offer the potential of improving system accuracy to sub-micron level precision at a reduced cost as compared to purely
hardware solutions as in the existing systems. The main objective of the proposed project is to develop UCMM having following unique features: 1. be error free for X-, Y- and Z-axes. 2. Wedge air bearing based system and star configuration of parallel kinematic
mechanism, due to which a symmetric configuration can be realized causing minimal error components. 3. Unique topology of the structural frame is proposed for error independence in Xand Y-axes due to Z-axis motion. 4. Error detection of stage through ultra-precision miniature interferometers (having 0.1 nm resolution) by following 3-2-1 principle. 5. Smaller foot print of the stage and overall system which will cause lesser manufacturing, geometric and thermal errors. 6. Real-time Kinematic Calibration Strategy. |
