Advanced Materials Research Online: 2011-07-27 ISSN: 1662-8985, Vols. 301-303, pp 1289-1292 doi:10.4028/www.scientific.net/amr.301-303.1289 2011 Trans Tech Publications, Switzerland Research and Design of Laser Accurate Displacement Measurement System Xiaogang Wang 1, a, Yuewei Bai 1,b and Kai Liu 1,c 1 School of Mechanics & Electronic Engineering, Shanghai Second Polytechnic University, Shanghai,China a victor.hust@gmail.com, b yueweibai@126.com, c liukai@meef.sspu.cn Keywords: laser displacement sensor, non-contact measurement, linear-servomotor-driven actuator, servo control system. Abstract. Laser displacement sensor(lds) displacement measurement is a non-contact measurement with more precision and a wide range of applications. In this paper, a laser accurate displacement measurement system based on LDS and three-dimensional linear-servomotor-driven actuators (3D LSDA) is presented. The 3D LSDA moving system is composed of linear servo motor, precision movable liner mechanism and servo machine. It is driven to move the noncontact laser displacement sensor to scan surfaces through the three-dimensional electric displacement platform, and then the measurement data is processed. The displacement sensor resolution is 2µm; each dimensional electric displacement platform repeated positioning accuracy is higher than 5µm. Introduction Since high requirements for the manufacturing or assembling accuracy, industry has very strong demands on the high precision dimension measure, especially the non-contact measurement technology is in its broad prospect application and widespread application foregrounds in some realm such as national defense, precise production and aviation & spaceflight. Coordinate Measuring Machine (CMM) is typical delegate of contact measurement for three dimensional curved surface measurements. But for some complex curved-surface, three is some performance defects with it, such as lower measuring speed, easily wear of probe, difficult to get the surface. And as the probe touches the surface of the work piece, it is easy to make work piece of wear and tear. With the development of science and technology, laser accurate displacement measurement(ladm) based on laser optical triangulation displacement inspecting technology has advantages such as non-contact measurement, fast measuring speed, flexibility for kinds of products and medium measuring precision, is getting more and more applications in modern industry production area. Measuring Principle of Laser Trigonometric Position Measurement Fig. 1 Measuring Principle of Laser Displacement Sensor All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-06/03/16,21:05:23)
1290 Advanced Measurement and Test The basic measuring principle of laser displacement sensor is shown as Fig. 1 above. Laser displacement sensor consists of LED laser device, high-precision objective lens, liner photo-electric CMOS device and high-speed data acquisition and processing system. A beam of visible laser light that creates a spot on a target surface, when the object moves or the plane changes, it causes the light spot moving along the optical axis. Reflected light from the surface is viewed from an angle by the digital CMOS line scan camera inside the sensor. The target s displacement is computed from the image pixel data. Since the light is is always perpendicular to the surface, so there is only one focus position. Any other off-focus positions will seriously affect the accuracy. To raise the accuracy and precision of laser displacement sensor, the system must meet the following requirements of Scheimpflug formula. (1) The explanations are as follows. θ 1 Angle between the laser optic axis and lens axis; β Vertical laser magnifying ratio; θ 2 Angle between the optical detector and lens axis Formula 2 shows the the relationship between displacement of the plane to be measured and the spot displacement. X is used as the symbol for the spot displacement, (2) The explanations are as follows. x Displacement of the plane to be measured. x Displacement of the spot at the CCD focal plane relative to the datum point. L Distance between the the point of intersection of laser axis and reflect light axis and the front plane of the lens L Distance between the CCD image plane and the back plane of the lens. The Keyence IL-065 CMOS laser displacement sensor based on the principle above is designed to measure regardless of target color or material. The parameters of the laser displacement sensor are as follows: the measurement range is 60 mm (F.S), and the laser displacement sensor resolution is 0.1%F.S. Operating Principle of Laser Accurate Displacement Measurement System Based on CMOS Laser Displacement Sensor 24V DC PC Euro209 Motion Controller servo drivers 3D LSDA Precise Sensor of Grating Angles DMIS measuring software COM transfering device laser displacement sensor Fig. 2 Operating Principle of LADMS Based on COMS LDS The structure of the LADMS system is shown as Fig. 2, which has four main components: PC, Laser Displacement Sensor, 3D LSDA system and Direct DMIS software, The laser displacement sensor module consists of IL-065 integrated device and DR-31 RS-232 module. 3D LSDA system is made of Euro-209 motion controller, AC Servo System of Panasonic, grating displacement module and three-dimensional linear-servomotor-driven actuators.
Advanced Materials Research Vols. 301-303 1291 Direct DMIS software gets data 3D points of X-Y-Z from 3D LSDA and Z from laser through TCP/IP protocols, and the data of process was carried out on it. Fig. 3 System Structure of 3D LSDA Based on Servo Motor Fig. 3 shows the structure of 3D LSDA. Laser module is fitted onto the Z-axis slider, and the Laser spot is on the up-left corner when system is in zero point. The DIMS software sets this point as system s origin of coordinates. When the X or Y axis moves, laser light moves along the surface to be measured, point data is acquired from the rating displacement module and the laser module. If the result of Z is out of the range of 55-105mm, system will change the position of Z slider to let the measure range no more than 60mm. 激光位移传 laser displacemen 感器 t sensor 3D LSDA Results and Displaying COM transfering device Euro209 Motion Controller DMIS mesuring software MeasurIng Points Data I/O Module Packaged Data Fig. 4 Processing Flow of Measuring Data Acquisition, Analysis/Processing and Display Processing flow of measuring data acquisition, analysis/processing and display is shown as Fig. 4. Every 10ms system gets data from the laser module and the motion controller, and then synchronizes the data. If the Z data is not out of range, the synchronized data will be caculated and the measure point is getted. Applications 3D LSDA is a closed-loop system, and the positon control is maded by Euro-209 motion controller. The positioning accuracy for this card is about 5-7 µm. Fig. 5 shows the setting UI of Euro-209. Fig. 5 Setting UI of Euro209 Card
1292 Advanced Measurement and Test The data acquisition and processing program of the system is shown as follows. First of all, places the work piece on the measuring system, lets the distance between the laser module and the work piece about 50mm, then opens the laser sensor to get the data in order to avoid out-of-range. Secondly, opens the control software, and lets the X, Y, Z axis to move about 100mm, which will initialize the system. Thirdly, sets up the speed and sampling interval, opens the Direct DMIS software, and gets data from the measuring system until finishes the task. Finally, uses the software to setup Cartesian coordinate system, analyses the measuring data and establishes the result diagram of analysis, picture and text report. Summary Laser accurate displacement measurement system is a precision system combining optical, mechanism, electro-circuit and micro-computer. Compared with tangent three-coordinates measuring machine, this laser system it is characterized by the low cost, the compact structure, the simplicity of operation, and is easy to perform the online-measurement. And the precision is high, under all conditions are satisfied in the laboratory, its precision can be as high as 6 um. This automatic measuring system can effectively satisfy the needs of production and with a very broad application foreground. Acknowledgment The authors would like to extend thanks to our project partners for helpful comments. This work is done within the Leading Academic Discipline Project of Shanghai Municipal Education Commission (No.J51802) and Shanghai Municipal Education Commission Fund (No. egd10020). The content of this publication is the sole responsibility of the authors. References [1] SHKLARP, SANJIVA KUMAR. Interferometric measurement of thickness of thin films of former deposited on glass plastes. Journal of Optics. 2000, 29(2): 85-93. [2] ZUO J Z, LIU F, ZHANG D ZH. The Application of machine vision technology in measuring screw thread. Machinery Design & Manufacture, 2006, 4(4): 113-114. [3] Keyence. High-Accuracy Surface Scanning Method User Manual. 2008. [4] Keyence. Surface Scanning Laser Confocal Displacement Meter IL-065 Series User Manual. 2008. [5] H. C. van ASSEN, M. Egmont-PETERSEN and J.H. C. REIBER. Accurate object localization in gray level images using the center of gravity measure: accuracy versus precision. IEEE Transactions on Image Processing, 2002, 11(12): 1 379~1 384. [6] Zhifeng Zhang, Qibo Fenga, Zhan Gaoa,and etc. A new laser displacement sensor based on triangulation for gauge real-time measurement. Optics & Laser Technology, 2008, 40(2): 252-255.
Advanced Measurement and Test 10.4028/www.scientific.net/AMR.301-303 Research and Design of Laser Accurate Displacement Measurement System 10.4028/www.scientific.net/AMR.301-303.1289