A Study on the Measuring System of the Variation of the Aiming Baseline in the Aiming Sights

Transcription

1 Preision Instrument and Mehanology July 0, Vol. Iss., PP. -7 A Study on the Measuring System of the Variation of the Aiming Baseline in the Aiming Sights Yundong Zhu *, Jinsong Wang College of Opto-Eletroni Engineering, Changhun University of Siene and Tehnology, Changhun, China * z_y_d69@sohu.om; soldier_97@6.om Abstrat- A method of measuring the variation of the aiming baseline, whih uses an infrared ollimator as the main measuring instrument, is put forward in this paper. Based on the measuring priniple of the optial measuring system about the variation of the aiming baseline in the aiming sights, an optial measuring system has been designed, whih inludes an infrared ollimator as the main measuring instrument. The experimental result shows that this method an well solve the problem--the limitation of the measuring range aused by the small field of view of the refletion type ollimator. And the angular auray of 0.05 mils is realized in this system. Keywords- Collimator; Aiming Baseline; Aiming Sight I. INTRODUCTION The variation of the aiming baseline [] of the snipersopes and thermal infrared imagers [] (alled by a joint name infrared sight) refers to the alteration aiming baseline of the aiming sights aused by the loosening, deforming and displaement of objetive lens, oular lens, retile, image onverter tube, pak ard guide and other omponents. The external influening fators mainly inlude transporting, shooting, and the high and low temperature environment. The variation is usually shown by using an angle value, and mil is ommonly used to indiate the value. The variation of the aiming baseline is one of the sientifi and reasonable assessment parameters for designing, proessing, and installing of the aiming sights []. Beause the aiming baseline has diret orrelation with the weapon firing auray, the variation of the aiming baseline has the diret bearing on the stand or fall of the firing auray. In the prodution and experiments of the infrared aiming sights, the measuring of the aiming baseline of the aiming sights is a very important item. Up to now the ombination of the refletion type ollimators [4] and angle measuring devies are generally used for the measurement. However, beause of the limitation of the field of view of the light pipes, it is hard to realize the measurement of the wide field of view. II. THE DEFINITION OF THE VARIATION OF THE AIMING BASELINE AND ITS MEASURING PRINCIPLE A. The Definition of the Variation of the Aiming Baseline Aiming Baseline refers to the link line between the entral point of objetive lens and the entral point of the retile of an aiming sight. The definition means that the variation of the atual aiming baseline is the position modifiation of the aiming baseline. Fig. shows the state after the aiming sight is adjusted. L 0, Le and R eah refers to the objetive lens, the oular lens, and the retile. Under this ondition, aiming baselineoo and optial axis OO an be onsidered as being in the state of doubling, and the optial axis has no deviations from the theoretial aiming baselinell. As Fig. shows that transporting, shooting, and the hanging of the temperature environment ause the loosening, deforming and displaement of objetive lens, oular lens, retile, image onverter tube, pak ard guide and other omponents, so as to lead to the relative position hanges of the aiming baseline and optial axis. The sight optial axis O O deflets angle while aiming at the theoretial aiming baselinell. The atual aiming baseline OO deflets angle aiming at optial axis. It an be seen from Fig. and Fig. that the atual aiming baseline deflets an angle of while aiming at the theoretial aiming baseline. The angle is the variation of the aiming baseline. Fig. Ideal working onditions of aiming sight - -

2 Preision Instrument and Mehanology July 0, Vol. Iss., PP. -7 Fig. The variable diagram of aim base line B. The Measuring Priniple of the Aiming Baseline It an be known from the meaning of the variation of the aiming baseline that to test the variation of the aiming baseline of an aiming sight, infinity benhmark target should be set up. Usually a ollimator an be used to ondut the simulation. As Fig. shows L and R eah refers to the objetive lens and the retile of the ollimator. Fig. The measuring priniple of the variation of aiming baseline The entre of the ollimator retile is F, and its image on the retile of the aiming sight is A. The entre of the retile of the aiming sight is O, and its orresponding point in the objet spae (also alled the aiming point) is O on the ollimator retile. The optial axis of the ollimator is the referene axis ll while onduting measurement. It an be onluded by the figure in the geometri relationships as follows: F O O tan f F O artan( ) f When is very small, it an be onsidered as () f F O is the orresponding deviation in the ollimator retile in the objet spae of the deviation between In the formula: the image of the entre of infrared ollimator retile on the retile of the aiming sight. f is the foal distane of the infrared ollimator. It an be known from the above analysis that the variation of the aiming baseline of the aiming sight an be used to measure both diretly and indiretly. Fig. shows that if the parallel rays sent by the ollimator rotate angle antilokwise, Point A, the image on the retile of the aiming sight of the entral point of the optial retile will be doubling with Point O, the entral point of the retile of the aiming sight. The rotation angle an be read diretly by an angle reading system. This is the theoretial basis of the diret measuring. - -

3 Preision Instrument and Mehanology July 0, Vol. Iss., PP. -7 The atual way to turn the refletion ollimator is inadvisable beause turning the ollimator will hange the measurement benhmark, and then influene the auray of the measurement. And it is hard to realize beause of the volume and quality of the ollimator from the engineering point of view. In order to solve this problem, a plane refletor whose angle an be adjusted an be fixed in the shooting light path, as it shows in Fig. 4. If we want to let the entral point F of the ollimator retile to be doubling with the aiming point of the ollimator retile of the aiming sight, we an just turn the plane refletor Rp to an angle of by keeping the ollimator and aiming sight unmoved. Fig. 4 The priniple of reading data via the refletor III. THE DIRECT MEASURING SYSTEM OF THE REFLECTION TYPE COLLIMATOR Fig. 5 shows the system diagram of the diret measurement of the variation of the aiming baseline of the infrared sight by using the refletion type ollimator. The infrared ollimator of the non-newtonian optial system onsists of a blak body, a target, a plane refletor and a paraboli refletor. It provides the measurement with an infinite distane infrared target, and an infrared sight whih an be used to observe the infinite distane target by the plane refletor. The plane refletor is fixed on an eletri-ontrolled two-dimension preision adjustment stage with 60 azimuth and pithing motion. Eah of the two spindles of the stage is equipped with a high preision absolute type shaft angle enoder. When the two spindles are turned by the program ontrol, the two dimension angle value of the plane refletor is shown. The measured aiming sight is fixed on the sight mount. The mount has five degrees of free adjusting funtions of vertial and horizontal, raising and falling, pithing, and azimuth movement, whih is used to adjust the postures of the aiming sight while being measured. Two-dimensional preision adjustment platform Plane refletor Blak body ontroller target Blak body Computer Paraboli refletor Sight mount The aiming sight being measured Fig. 5 The measuring system diagram of refletion ollimator - 4 -

4 Preision Instrument and Mehanology July 0, Vol. Iss., PP. -7 While measuring, adjust the soleplate so as to let the aiming sight approximately aim at the target; adjust the temperature of the surfae of the blak body; and make sure the infrared retile should be learly visible. Then adjust the eletri-ontrolled two-dimensional preision adjustment platform so as to let the ross urve on the retile of the aiming sight aurately aim at the target of the ross urve on the retile of the infrared type ollimator. Then note down the angle values of the two spindles at this platform. Take off the infrared aiming sight and then ondut the experiments of shooting, impat vibration, and high and low temperature testing, et. After the experiment, fix the infrared aiming sight on the mount again, and observe the hanges of the images on the target. Then adjust the two-dimensional preision adjustment platform with a plane refletor fixed so as to let the ross urve on the retile of the infrared aiming sight redouble with the ross urve on the retile of the target of the infrared type ollimator. Note down the angle values of the two spindles of the platform at that time. Aording to the first and seond hange of the postures of the two-dimensional preision adjustment platforms, the two different angle values an be established. From the results obtained, subtrat the lower figure from the high figure, and multiple the result by, then the variation of the aiming baseline of the infrared aiming sight would be realized. IV. THE ERROR ESTIMATION OF THE MEASUREMENT The fators whih influene the measuring auray mainly inlude the ollimating error while aiming at the target via an aiming sight, indiation error while reading via the two-dimension adjustment stage and the error of the ollimator. A. The Collimating Error of the Aiming Sight The relationship among the visual amplifiation, ollimating error and the human eye alignment error P t an be presented as: P t () K In the formula: K is the onfidene oeffiient, is the amplified oeffiient of the ollimating error. Its numerial value is arrived at via an experiene or an experiment [5]. In ideal onditions, the human eye alignment error, while aiming via double wire lamp single wire, P 0. If the pixel number of the aiming sight is 88 84, then the size of the pixel is 5 m. The foal distane of the objetive lens is , the size of the OLED sreen is t f w =75mm, the foal distane of the oular lens is f m =0, the field of view is (.54m), the magnifiation of the equivalent field is. 8, assume, the ollimating error is of uniform distribution [6], the onfidene oeffiient ( disperse oeffiient ) is K, then P 0 the result is t 6. 8 K.8 B. The Indiation Error ) The Error of the Two-dimension Adjustment Stage : The two-dimensional adjustment platform adopts a preise DC torque motor, worm gear and worm rotation, and shaft angle enoder. It also adopts eliminate lateral learane and baklash system, then the auray an reah, and the emergent light is 4. The error follows normal distribution, then ) The Indiation Error : 4. This error follows uniform distribution. If the absolute indiation error 0.0, then Through the above analysis, the omposition error of the indiation is. C. The Collimator Error The ollimator error mainly inludes the manufature error, the fousing error, the alignment error and the foal distane error. The last three errors an be negleted via the adjustment of the ollimator. The most influening fator is the manufature error of the retile. The manufature error of the retile an be sure to be 0.0 mm via preision mahinery. The d - 5 -

5 Preision Instrument and Mehanology July 0, Vol. Iss., PP. -7 designed foal distane of the ollimator is f 800mm, whih error obeys the normal distribution, so K, then the error from it is , and the ollimator error is Aording to the analysis above, the measuring error an meet the need of the demand of the measurement of the infrared sight. The total measurement error is mil V. CALIBRATION EXPERIMENT AND ITS RESULT A onfirmatory experiment on the 0 4 standard of the Germanium glass optial wedge was onduted by using a ertain type of infrared sight in the lab. In the experimental diagram whih is shown in Fig. 6, R is the plane refletor of the p ollimator. If the optial wedge is fixed horizontally, it is used to measure the azimuth angle; and if it is fixed vertially, it is used to measure the elevation angle. To adjust R, the two-dimension preision rotary stage an read the value automatially. p Out of observations of measuring, the data found are shown in TABLE I. The mean value is greater than the nominal value, whih is aused by the installation error of the optial wedge. That the measurement value in the Y diretion is greater than that in the X diretion is also aused by the installation error of the optial wedge. Value in eah of the two diretions is less that 6.4, whih meets the result in the analytial estimate. o o R p Fig. 6 The ollimator alibration diagram N. TABLE II CALIBRATION EXPERIMENTAL DATA x Diretion (azimuth angle) y Diretion (elevation angle) Mean VI. CONCLUSION The measuring priniple of the variation of the aiming baseline of the aiming sights is analyzed and elaborated; and a new method is introdued to measure the variation of the aiming baseline of the aiming sights diretly by using a new refletion type ollimator in this paper. The orresponding analytial estimates are onduted on the fators ausing deviation in this method. Then the alibration experiment is onduted. The result shows that this method an reah the measurement auray within several seonds. This researh shows that the method to measure the variation of the aiming baseline of the aiming sight - 6 -

6 Preision Instrument and Mehanology July 0, Vol. Iss., PP. -7 by using the refletion ollimator has the merits of non-ontat, fast measuring, high preision, wide range, and an realize the measurement of large variety of aiming sights and multiple parameter. It has the vital pratial signifiane in manufaturing and measuring of the aiming sight. REFERENCES [] GAO You-tang, QIU Ya-feng, TIAN Si et al. Mehanism Analysis of Zero Displaement Movement of LLL Sight Devie Based on Vibration Experimental Condition [J]. Journal of China Ordnan, 008, 9(9): [] CHEN Lv-ji, MING Jing-qian, MA lin et al. A Four-piee Dual Field of View Optial System for LWIR Thermal Imager [J]. Infrared Tehnology, 00, (): 5-8. [] YANG Rui-ning, AN Zhi-yong, CAO Wei-guo et al. Researh on the Modern Measuring System of Exit Pupil Diameter, Distane and Magnifiation of Optial Aiming Sight [J]. Journal of China Ordnane, 009, 8(4): [4] GAO Ming-hui, LI Li-fu, XU Jing-li et al. Design of a new kind of multi waveband large aperture parallel light pipe [J]. Infrared and Laser Engineering, 009, 8(4): [5] YANG Zhi-wen. Optial measuring [M]. First published. BeiJing: BeiJing I n s t i t u t e o f p r e s s, 995: 6-. [6] MA Hong, WANG Jin-bo. Error theory and instrument preision [M]. First published. Beijing: Weapons industry publishing house, 007: