Study on Digitized Measuring Technique of Thrust Line for Rocket Nozzle

Transcription

1 Study on Digitized Measuring Technique of Thrust Line for Rocket Nozzle Lijuan Li *, Jiaojiao Ren, Xin Yang, Yundong Zhu College of Opto-Electronic Engineering, Changchun University of Science and Technology, Changchun, China College of Mechanical and Electric Engineering, Changchun University of Science and Technology, Changchun, China * custjuan@6.com; yangxin0086@6.com Abstract-A digitized measurement method was detailed for nozzle thrust line of solid rocket motor based on advanced non-contact measuring technology with laser radar. The principle of this measurement method and the self-calibration technology of tolling ball are deeply researched. It proposes a new measuring scheme for thrust line which aiming at the front and back face circularity, circular zero line and the inner -D shape of the motor nozzle. The thrust line is obtained through the proper optimization model, and experiment testing shows that this measurement method provides higher measuring precision and efficiency which ensure the accuracy of thrust line direction. Keywords- Nozzle thrust line; Digitized measurement; Laser Radar I. INTRODUCTION The error of thrust line will affect the action point and direction of thrust line, it may lead to the offset and deflexion of the thrust line []. Traditional measurement of thrust line uses dial indicator and other instruments for measuring, the measurement precision is low; then the use of theodolite improves the measuring accuracy, but the measuring efficiency is still poor. The method of digitized measurement for thrust line has many advantages over traditional measurement, such as higher accuracy, higher efficiency, and larger quantity and so on. This paper details a digitized measurement method for nozzle thrust line of solid rocket motor based on advanced non-contact measuring technology with laser radar. The principle of this measurement method and the self-calibration technology of tolling ball are deeply researched. It proposes a new measuring scheme for thrust line which aiming at the front and back face circularity, circular zero line and the inner -D shape of the motor nozzle. The thrust line is obtained through the proper optimization model, and experiment testing shows that this measurement method provides higher measuring precision and efficiency which ensure the accuracy of thrust line direction. II. THE MEASURING PRINCIPLE OF LASER RADAR The ranging principle for Laser Radar is shown in Fig..The infrared laser beam is split into beams when it passes through the beam-splitter, if the transmission time of the measuring beam (path to the target and back) and the reference beam (path to the known length optic fiber and back) is T m and T f, the time difference between T m and T f is T and its relationship is T=T m -T f. The mathematical model for the measured distance L m is: L m L f n n f 0 L c L Where n f is the refractive index of the optic fiber, n 0 is the refractive index of the air, L c is the distance of energy loss compensation and L is the distance between two laser beam. () 5 Including: The infrared laser of base frequency for 00 THZ Fig. Principle of laser ranging - 5 -

2 The modulator of modulation frequency is GHZ 0,frequency modulation pulse cycle is microseconds modulator The fiber of fixed-length The signal reflected from target 5 mixed signal The azimuth and elevation angle of the laser radar are measured from the mirror pointing system by shaft encoder, as shown in Fig.. Then we can calculate the three dimensional Cartesian coordinates of the measured point []: X Pcos cos Y Pcossin Z Psin Where P is the distance from a space point to the origin, θ is the polar angle from the positive z-axis, α is the azimuthal angle in the X-Y plane from the x-axis. () Fig. -D Coordinate measuring principle III. THE CALIBRATION PRINCIPLE OF LASER MEASUREMENT SYSTEM For the laser system, it must be calibrated to carry on precision measurement. The standard tooling balls will be adopted in order to ensure the measuring accuracy of the system. Since different standard tooling balls with different diameter specifications, it can be chosen according to the size of object to be measured and the distance between laser radar and the object, just ensuring the energy of the returned laser is enough, while the difference of the diameter has no effect on the measuring accuracy. The tooling ball is placed on the tripod, as is shown in Fig.. Fig. The tooling ball is placed on the tripod The purpose of placing tooling ball is to guarantee the laser radar station in the same coordinate system in moving measurement, before and after laser radar transforms position, measuring or more target tooling balls respectively. As the spherical characteristic of tooling ball, laser measurement system can get the center point of tooling balls from any direction. So we can get station moving common points with high precision, meanwhile, the tooling ball with smooth surface and high reflectivity so that it can still get a strong recovery signal in a far distance, this characteristics ensure the accuracy of measurement. When laser radar measures the ball, firstly it scans the spherical surface of the tooling ball, then gets the strongest recovery signal and records the distance D of recovery signal. Meanwhile, it compensates automatically the radius value R of the ball and gets the distance L between laser measurement system and the center of measured tooling ball, L=D+R. According to the angle value of angle encoder, we can calculate the space coordinates of tooling ball s center, as shown in Fig.. Except the use of calibration, the tooling ball also can be used for station transformation. Before and after laser radar moving station, measuring three or more placed tooling ball is needed, putting the data which is in the two measurement into the measurement software SA to fit, we can achieve the unification of coordinate system with software SA[]

3 L D R Mirror in Laser Radar Fig. The calibration principle of the Tooling ball The tooling ball to be measured IV. THRUST LINE MEASURING TECHNOLOGY Taking the measurement of nozzle thrust line as an example, the paper analyzes the digital measurement technology of thrust line. The distribution location of the Laser Radar for the motor thrust line measuring as is shown in Fig Fig. 5 The distribution location of the Laser Radar Including: Laser radar position Laser radar position Measurement of laser radar in area A Measurement of laser radar in area B 5 the front face circularity of motor 6 the back face circularity of motor 7 the export face of motor nozzle 8 circular zero line of motor, 9 motor nozzle s throat 0 common point P common point P common point P The measurement task in A area with laser radar is the shape of front face circularity for motor, the measurement task in B area includes: the shape of back face circularity for motor, circular zero line and the inner surface for motor. Using at least common points to make sure the coordinate unification of measurements in area A and B, meanwhile during the measurement we should try to avoid the errors which are caused by vibration of air and measuring point and air disturbance. Solid Rocket Motor defines connection of geometric center of motor housing front and rear face circularity edge as basic axis. Firstly, putting the laser radar on the measurement area A, three-dimensional topography scanning on the front face circularity edge of the motor, there are lots of ways of measuring-surface for laser radar, for higher accuracy the paper adopts the measuring point on the front face circularity edge, establishing open interval of tectonic lines Open perimeter according to measuring points, the way which topography scanning on front face circularity edge by the way of metrology open scan along the tectonic line

4 Then measuring area B, three or more tooling balls are needed for moving station to make the area A and area B establish in the same coordinate system. After moving station, laser radar in area B three-dimensional topography scans on back face circularity edge of motor and gets its measuring date, as shown Fig. 6. Space circle fits on the obtained cloud points of area A and area B, gets center point of front and back face circularity edge, and then obtains axis of motor. In the Fig. 6: -Laser radar A -Laser radar B Fig. 6 Measurement data of the front and back face circularity edges of motor -Measurement data of the front face circularity edges of motor -Back face circularity edges of motor While the laser radar can measured periphery toward zero engraved bit line in the B area. The periphery toward zero engraved bit line of rear cylinder of motor nozzle is basis of thrust line skewed azimuth, the width of about 0.mm,using the function of laser radar measuring surface point to sample a number of points in zero circumferential groove, projecting sampling points towards the circle center of back face circularity edges which is perpendicular to the axis of the plane engine, getting the coordinate point of periphery toward zero engraved bit line by fitting algorithm, getting circumferential zero reference line by the connection between the coordinate point of zero reticle and center point of back face circularity edges of motor. Laser radar in the B zone can make three-dimensional topography scan on motor nozzle inner-surface, since the measurement depth of field will directly affect the measurement accuracy of the laser radar, this paper adopts measurement technology of nozzle inner-surface same depth of field to measure it for higher accuracy of three-dimensional nozzle inner-surface. As is shown in Fig. 7, using command surface point measures each point in nozzle end and nozzle inner-surface, establishing several open interval tectonic lines perpendicular to the face normal, using the way of Metrology open scan to take the nozzle inner-surface measurements of same depth of field. Fig. 7 Cloud points of inner moulding surface of effuser In the Fig. 7: -The scanning data of nuzzle inner moulding surface of motor. - Laser radar V. POINT CLOUDS DATA PROCESSING The point clouds data in IGS format of the nozzle s inner surface are exported in software Spatial Analyzer, and then the point clouds are preprocessed by Imageware software in the traditional way, and make a motor nozzles thrust line as accurate as possible, the results will be exported in IGS format[], as shown in Fig

5 Including: Nozzle s thrust line after initial treatment Fig. 8 Thrust line after initial treatment Importing the exported IGS format data into CATIA, adopting secondary development technology based on CATIA to optimize data. Techniques of thrust line generated and optimization adopts CATIA process access technology [5], running the script and CATIA within the same process, by CATIA script motor to parse executing the macro script command. Programming automation objects with Visual Basic, by the basis of building for object oriented program nozzle thrust line parameters. VB with advantage of good interface and controllable input parameters [6] can be smart to carry thrust line parameter changes at any time. Based on the redeployed nozzle-type surface point cloud data, entering the rotation surface model R, wherein the rotating body model includes polynomial curve and desires thrust axis, according to nozzle manufacturing error and measurement error to set threshold value RMS, calling optimization model, making the input rotated surface model infinitely close to the measured point cloud data, thereby optimizing the nozzle thrust line. After optimization the mean square of average error between the obtained point clouds data and rotating surface is 0.0mm, axis error is 0.05mm, getting the data processing precision is 0.05 mm as motor nozzle thrust line, as is shown in Fig. 9. Fig. 9 Thrust line of effuser after Optimizing Importing nozzle thrust CAD model line generated in the CATIA into the software of laser radar measurements Spatial Analyzer by IGS format, as is shown in Fig. 0. The distance between axis of the motor and the motor thrust line is thrust line traversing ρ; the angle between motor thrust line and the motor axis is thrust line deflection θ; through the point B making a plane be perpendicular to the axis of the engine. The angle Ф which plane of the projection lines between thrust line and circumferential zero reference line are thrust line deflection azimuth. θ ρ φ Fig. 0 Measurement diagram of parameter of thrust line

6 In the Fig. 0: - Motor axis - Motor trust line - Projection line of motor thrust line - Engine circumferential zero reference line VI. CONCLUSION This paper has introduced a new digital measurement technology based on laser radar which is mainly used for motor nozzle thrust line. This non-contact -D morphology scan will replace the partial contact measurement, and it s obvious advantage like high accuracy, easy application, high efficiency ensuring the more accuracy measurement for motor nozzle thrust line. REFERENCES [] ZHANG Chun-fu, TANG Wen-yan, LI Hui-peng, et al. The Application of Laser Tracker in the Measuring Technique of Thrust Line of Solid Rocket Motor, Vol. 0 No [] LUO Jian-bin, WEN Shi-zhu, HUANG Ping. Thin film lubrication, Part: The transition between EHL and thin film lubrication. Wear, 996. [] ZHU Xiao-yin. Research on the Digital Precision Measurement Technology Based on The Laser Radar. Changchun University of Science and Technology, 009. [] ZHANG Guo-yu, SUN Tian-xiang, WANG Ling-yun, at al.theoretical analysis of coordinates measurement by flexible D measuring system.chinese journal of mechanical Engineering, 007. [5] JIN Tao, TONG Shui-guang. Reverse Engineering Technology, China Machine Press, 00. [6] ZHANG Chun-Fu. Study on the Measuring Technique of Thrust Line of Solid Rocket Motor with Laser Tracker. Harbin Institute of Technology Institute,