Measuring System Of Surface Topography Based On Displacement Sensor With Micro Constant Measuring Force And 2-D Motif Assessment Method

In present-day surface metrology, surface morphology measuring techniques and assessmenttheories have always been the frontier research field. Owing to the discrepancy between thehigh precision and measuring range for surface measuring instruments based on variousmeasuring principles, it is of great significance to develop a high precision surfacemorphology measuring system with broad prospects for application. The main researchcontents and creative points about measurement techniques and assessment methods ofsurface topography in the dissertation are as follows:A displacement sensor with a wide measuring range and micro-constant measuring force hasbeen proposed and developed which is suitable for measurement of engineering surfacemorphology. The displacement sensor consists of an electric induction sensor and a voicecoil motor (VCM). The induction sensor is used as the measurement standard and the VCMis used to control measuring force and enlarge the measuring range of the displacement. Themethods of designing and implementing all the structural units of the displacement sensorare discussed at length. A mathematical model for the feedback control mechanism of thesensor's measuring force is established based on theoretical analyses. The steady-state errorand stability of measuring force control are studied and a PID corrective controller isdesigned. The dynamic characteristics of the displacement sensor are discriminated, testedand digitally simulated.An algorithm for broadening the measuring range by lifting the inductance sensor isproposed, which has been used in a large-range surface morphology measuring system. Withthis algorithm, the precision of the measuring system has risen to above 0.02μm and itsmeasuring range to 2mm. In order to adapt to different measuring speeds and the variationof surface morphology, the system now has 5 predetermined measuring ranges of induction.The VCM is driven by a 16 bits D/A converter to improve the control precision. A new IIIcount method for optical grating is adopted in the measuring system. In the counting methodof the measuring system, the multi-zero signal of the grating is utilized to prevent the signalfrom getting lost, making the count more accurate. The errors of the system and theirinfluence on the measuring system are analyzed. Experimental verification of the precision,measuring range and performance of the system are performed in accordance with therequirements of ISO12179:2000.A 2-D Motif combined algorithm is proposed based on finite difference and the latticetheory. The research progress of 2-D and 3-D Motif assessing method is studied.Following an analysis of the progress made in this method, the uniqueness and stability ofthe solution for 2-D Motif combined tests are discussed. With the Motif represented as anevent, all the given sets of events in which Motif can be combined may be enumerated in alattice. The 2-D Motif evaluating software has been developed by searching the peaks andvalleys of Motif method based on finite difference. The software is integrated with thelarge-range surface morphology measuring system, facilitating Motif assessment of theresults of measurement. The differences between 2-D Motif parameters and the roughnessof traditional 2-D standard are analyzed. The similarities and differences among the severalcurrently recognized 3-D Motif definitions are compared. Based on a digital elevationmodel and graph theory expression of contour, a 3-D Motif assessment algorithm isdiscussed.