Usage of scanning coordinate-measuring machines for inspection of screw threads has become a common practice nowadays. Compared to touch trigger probing, scanning capabilities allow to speed up measuring process while still maintaining high accuracy. However, in some cases accuracy drasticaly depends on the scanning speed. In this paper a compensation method is proposed allowing to reduce the influence of some dynamic effects while scanning screw threads on coordinate-measuring machines.
Due to inertial forces while high-speed scanning freeform workpieces with low radius of curvature on coordinate-measuring machines it is difficult for the control software to maintain stable contact between the probe and the surface. This is one of the reasons preventing accurate scanning at high speeds @cite_2 . The study of dynamic effects was conducted by many researchers. Application of signal analysis and processing theory to dimensional metrology was studied in @cite_4 . Pereira and Hocken @cite_2 proposed classification and compensation methods for dynamic errors of scanning coordinate-measuring machines. They used Taylor series and Fourier analysis to compensate measurement of circular features. ISO 10360 @cite_9 defines acceptance tests for scanning coordinate-measuring machines. Farooqui and Morse @cite_5 proposed reference artifacts and tests to compare scanning performance of different coordinate-measuring machines. @cite_12 conducted experimental research and concluded that freeform surfaces scanning time reduction is limited at high speeds by acceleration and deceleration of the probing system.
@cite_4 @cite_9 @cite_2 @cite_5 @cite_12
2016762411 2088650260 1983915599 2100487443
An approach to dynamic evaluation of measurement systems is presented. On the one hand, it separates physical experiments, analysis and signal processing methods into successive steps of evaluation. On the other hand, the structure allows for resolution of an entire measurement system into its components for dedicated analyses. There is no limitation to particular applications except that it should be possible to model the response of the measurement system with differential equations with constant coefficients. Proposed tools such as estimation of error and uncertainty and direct mapping methods for synthesis of signal restoration filters are new or recently published, while others like system identification are well known but not previously systematically used in the context of calibration. The necessity for reducing production cycle times while achieving better quality compels metrologists to look for new and improved ways to perform the inspection of parts manufactured. The advent of coordinate measuring machines led to a significant boost in accuracy, flexibility and reliability for measurement tasks. However, these machines are in some instances lagging behind machine tools and need improvement. One major limitation is the execution of measurements with low uncertainty at a reasonably fast rate to make it possible to measure more parts. This would ensure more reliability to the end product and better information to control the manufacturing process. Coordinate measuring machines with scanning capabilities offer the option to output high data density for parts at high speed. However, they are still considerably less accurate at faster measurement speeds and need to be improved. In this work a scanning measuring machine was extensively tested and a compensation model that accounts for part of its dynamic errors affecting measurement of circular features is proposed. Coordinate measuring machines (CMMs) with continuous-contact scanning capabilities are experiencing more and more use in a wide variety of discrete-part manufacturing industries. Many users of these CMMs, if asked, will say that their metrology requirements include high density scans at high speeds with high accuracy. These requirements are in conflict, as there will be some point at which the accuracy of the scanned data begins to decrease with an increase in the scanning speed. This paper addresses the effects of scanning speed on the performance of different CMMs using contact sensors. The use of a family of artifacts is proposed in order to evaluate the relative scanning performance as a function of scanning speed and the direction of the scan within the CMM volume. The artifacts that are developed for these tests have a sinusoidal waveform superimposed on a flat surface. This paper describes a series of experiments that utilize these artifacts and assess the ability of these tests to capture how a scanning CMM will perform when measuring actual parts. Common usage of Coordinate Measuring Machines in industry means that they are applied not only for the measurement of the details, but also for the digitalization of the geometrical elements. Nowadays, the development of scanning methods enables the easy measurement of free surfaces. Digitalization of such surfaces with scanning probe heads is much faster than touch trigger probing, while the uncertainty level remains almost the same. However, the accuracy of points localization is dependent upon the scanning speed.