| The Frequency Modulated Continuous Wave(FMCW)laser interferometer is an advanced optical instrument that can accurately measure the displacement of an object and generate a dynamic interference signal with displacement information for real-time phase calibration.Therefore,the interferometer has strong anti-interference ability and high measurement accuracy,and can be widely used in fields such as petrochemicals,automobile manufacturing,and integrated circuit manufacturing.However,the FMCW laser interferometer requires the object to be measured to move on a guide rail and carry a plane reflector,which limits the application range of the interferometer.Therefore,this paper designs and manufactures a contact-type FMCW laser interferometer to meet the need for measuring complex surface objects.The specific research content is as follows:Firstly,the main factors affecting the light coupling efficiency of the contact-type FMCW laser interferometer are analyzed: the reflector deflection angle.This is the core problem of this research,and its purpose is to ensure that the collimator can receive a stable beat frequency signal during the measurement process.Based on geometric optics and the structural characteristics of the collimator,a geometric model of the fiber collimator is established.With the condition that the center light of the laser is incident on the fiber core,the maximum deflection angle of the reflector that meets the index requirements is calculated and derived.The maximum interference cavity length range.And through formulas,it can predict the light coupling efficiency when different cavity lengths are incident on the collimator at the maximum light receiving angle.This result provides a theoretical basis for finally determining the wall tolerance.Secondly,a displacement measurement system for contact-type FMCW laser interferometers was designed.The method of changing from non-contact to contact type is to bond a plane reflector inside the probe and closely contact between probe and object to be measured.Its structure is similar to that of an inductive-capacitive displacement sensor.It replaces guide rails with sliding rods and sliding pairs to complete single-degree-of-freedom measurement of objects to be measured and realizes miniaturization of measurement systems.A contact probe was made using an axle hole fitting structure to ensure that when radial clearance of measuring rod is less than a certain value,collimator can definitely receive laser reflected by reflector.Finally,experiments have proved that prediction of reflector deflection angle affecting coupling efficiency is basically correct.Then use contact-type FMCW laser interferometer for displacement measurement.When probe measures object displacement 20 mm,linear regression R2 reached 0.99901 result was obtained.This measurement system can simply,accurately and quickly measure displacement of non-planar and rough surface objects. |
