Research On Crucial Technology Of The Thread Measurement Instrument By Probe Scanning

Precision measurement is the foundation of precision, ultra-precision machining manufacturing. The precision measurement of thread parameters is an essential element of the metrology areas, which has a very broad market demand. Tranditional detection methods of the thread parameters, such as calibration with go/no-go gauges, measuring mechine, micrometer etc, can not meet the needs of metrology market effectively due to limited accuracy, single measurement parameter or the high cost. The integrated measurement of the thread parameters according to the profile data is an important morden method. Compared with the vision method, Laser triangulation method and coordinate measuring machine method, the method of thread profile scanning with probe is applied in many metrology institutions for the high accuracy, the wide measuring range of threads and good performance-price ratio. However, this kind of measurement method has not formed a unified standard currently, and the revelent theories are not mature enough, which request further reseach and discussion. Consequently, some crucial problems involving the parameters calculation, errors calibration and compensation, motion control etc, are investigated based on the thread measurement instrument developed independently. The research mainly includes the following content:(1) For the calculation of thread parameters, the profile data points are denoised by the polynomial spline interpolation and robust Gaussian regression filter method. A calculation method for the pitch line is proposed with respect to the minimum variance of the segments distance between every two neighboring flank lines. This method provides an effective approximation to the definetion of the pitch line. Then the calculation methods for pitch and pitch diameter are designed based on the pitch line.(2) The influence on the pitch diameter caused by the workpiece alignment deviations is studied with the use of homogeneous coordinate transformation. The Sobol global sensitivity analysis is ultilized to get the quantized values for the influence degree. Then, the mathmatical model is simplified by omiting the small affecting parameters. Based on the simplified model, a two gauges calibration compensation method is proposed. The uncertainty of the compensation method is discusse. The results demonstrate that just with the calibration of two standard gauges, the errors of pitch diameter caused by the alignment deviations can be confined in less than 1 μm for the thread range supported by the fixture. Compared with the single gauge calibration method, the two gauges calibration method can keep good measurement accuracy for all the threads in measurable range desipite of large alignment deviations.(3) To meet the demand of limiting X axial rotation deviation less than 1o, a vision detection method for the probe tip points is proposed, which integrates the corners detection, the edges detection and the motion prediction of the regions of interest(ROI). Then the X axial rotation deviation is calculated by tracking the tip points both up and down. The experiment result demonstrates that the detection accuracy of X axial rotation deviation is 0.0654° with the background changing during the probe movement. And the repeatability of the test procedure is ±0.16%, which proves the detection method is adequately qualified for application.(4) In view of the motion control of the Z axis plateform, the load of which is counterpoised by a cylinder, the dynamic equation of hindrance force caused by the single acting pneumatic cylinder is established. With the combination of PMLM model, the system’s kinetics equation is established. A modified 3-tier composite control structure based on nonlinear force observer is put forward. The nonlinear part of the system is compensated effectively. The simulation and experiment results illustrate the practical applicability and efficiency of the proposed method.(5) The variation for the contact force of probe rod is investigated with the velocity and acceleration changing. The variation for elastic deformation and the position errors during the dynamic scanning are obtained with the combination of analysis theory for the lateral vibration of the cantilever in vibration mechanics. Taking into account of the hysteresis phenomenon for the inductive sensor, the intergrated model of the dynamic errors is established. In addition, the genetic algorithm is used to identify the model parameters. Examples show that the dynamic errors can be reduced more than 40%, which proves the effectiveness of the compensation model.