Study On Key Technology Of Hand-held Laser Range Finder Verification System

The hand-held laser range finder is a kind of etalon,which measures the target distance by time of laser flight or phase difference.As an important part of dissemination of quantity in length measurement,laser ranging devices are under periodical verification to ensure the accuracy of indicating value.According to JJG966-2010 procedure,the verification items are repeatability,consistency of datum planes and error of indication.There are several defects in traditional testing systems,such as large amount of labor intensity,low automation level,poor stability and so on.So it's necessary to design a high precision automatic verification system.With the further development of industrial automation level,visual inspection technology plays an increasingly important role in verification process.A novel automatic verification system aimed at laser range finder is proposed in this paper.In order to improve the manual verification system in Tianjin verification institution,an automatic walking structure is designed to realize automatically successive calibration,which is carried with an industrial camera,a stepper motor,and an industrial computer.Besides,a range finder's holder contained multiple degrees of freedom is proposed to align the target by adjusting posture.The relationship between pixel coordinate system and world coordinate system is calibrated by double frequency laser interferometer.The main work in this paper is as follows:1.Discuss the scheme of hand-held laser range finder's calibration system.According to the regulation,the calibration system should be set on marble test platform.An idea of novel calibration system consist of vision module,electronic control module,wireless communication module and real time adjustment holder.A high resolution CMOS camera and a coaxial parallel light source constitute the visual system,while control system consist of an embedded industrial computer,a MC9S08JM60 microcontroller,a position sensor and a motor driver.What's more,dynamic system contains a large capacity lithium battery,a stepper motor,a planetary gear reducer and an electromagnetic clutch.2.Design a range finder's holder contained multiple degree of freedom.Considering the regulation of the verification process,analyzing the degrees of freedom while adjusting the posture of laser range finder.It's proposed in this paperthat optimizing redundant degrees of freedom within accuracy level.The mobile feature of pitch adjusting mechanism is analyzed.Design a fixing device according to the request of datum planes' consistency.Above all,a range finder's holder has been completed.3.Design a software system.The steps of image processing program are described as below.A suitable threshold is chosen to convert a gray image to binary.And then the filtering algorithm and the repair algorithm of scratch on steel tapes are proposed,while edge detection algorithm is realized by horizontal projection.After that we can calculate the pixel position of the target line.A double frequency laser interferometer is used to calibrate the transform relation of pixel coordinate system and world coordinate system.The host computer and slave computer connect through WiFi,and the network programming realized by Winsock is based on TCP/IP communication protocols.And then wireless communication is accomplished.