Design of SINS/GNSS integrated navigation system for aerial time-critical guided bomb

CHEN Shuai,LEI Hao-ran,BO Yu-ming,XU Qin-li(School of Automation,Nanjing University of Science and Technology,Nanjing 210094,China)

Design of SINS/GNSS integrated navigation system for aerial time-critical guided bomb

CHEN Shuai,LEI Hao-ran,BO Yu-ming,XU Qin-li
(School of Automation,Nanjing University of Science and Technology,Nanjing 210094,China)

To satisfy the requirements of miniaturization and high reliability for airborne precision guided munitions,a compact close-loop FOG IMU/GNSS integrated navigation system is designed based on DSP C6747+FPGA shallow-parallel architecture.An adaptive Kalman filter is designed for information fusion,and the principle prototype’s overall size is 13 cm×14 cm×12 cm.A hardware-in-loop simulation scheme is designed for analyzing the integrated navigation system performance through computer simulation of target information and flight course.The simulation and ground test results show that the integrated navigation system offers better stability and real-time performance,and its accuracy meets the requirement for precision strike.

integrated navigation system; Kalman filter; guided bomb; hardware-in-loop simulation

Compared with general aerial bomb,precision guided bomb(PGB) has advantages of high precision,strong firepower,good maneuverability,high combat effectiveness and reliability,which installs guidance and control components with GNSS/SINS integrated guidance[1-2].By equipping PGB with gliding wings,advanced seeker and bi-direction data link,the standoff selective target detection and precision strike can be truly achieved,which is of great significance in wartime[3-4].

Taking the project of range-extended aerial time-critical guided bomb as background,a compact integrated navigation system is designed in this paper.The design of hardware and algorithms are introduced in detail.In addition,a hardware-in-loop (HILS) simulation scheme for verifying the performance of integrated navigation system and the strike accuracy against dynamic/static target is proposed.

1 Design of the hardware system

1.1 Idea of overall design

In view of the problems that the subsystems of traditional distributed missile-borne integrated navigation system are relatively dispersed and less integrated,a compact integrated navigation system is designed[5-7],theoverall size of which is only 13 cm×14 cm×12 cm and its weight is less than 3 kg.

The system based on DSP+FPGA shallow-parallel architecture has advantages of high integration,small size,abundant interface,fast calculation speed and high precision,and it has realized efficient real-time data acquisition,multi-channel real-time communication,high speed data processing and output etc.The integrated navigation system is shown in Fig.1.

Fig.1 Integrated navigation system

1.2 Hardware design

As the key equipment of PGB,the compact integrated navigation system mainly consists of three parts: close-loop fiber optic gyroscope (FOG) inertial measurement unit(IMU),GNSS satellite receiver and missile-borne integrated navigation computer.

The bias repeatability and bias stability of each FOG are ≤3 (°)/h and ≤2 (°)/h respectively,those of accelerometer are ≤0.1 mg and ≤0.05 mg respectively;The x axial measurement range of FOG is ±500 (°)/s,theyaxial measurement range and the z axial measurement range of FOGs are ±100 (°)/s,then the measurements of accelerometers are ±15g.

The GPS/GLONASS compatible satellite receiver JAVAD GG100 is used in this system.The dynamic horizontal and vertical positioning accuracy of GG100 are ≤3 m(CEP) and ≤6 m(CEP) respectively.The speed measuring accuracy is ≤0.1 m/s.The data output frequency range of GG100 can be manually adjustable from 1 Hz to 20 Hz.It has characteristics of good performance and anti-interference etc.

The floating-point DSP TMS320C6747 costs less power than other C6000 series chips with modular power supply.Its operation speed can be up to 300 MHz and processing speed is ≥1200MFLOPS.The kernel is two-level cache structure and internal RAM is 448KB.Rich peripheral modules,smaller size and above factors make C6747 be fairly ideal missile-borne DSP chip for navigation.

In the system,multi-channel standard duplex serial communication interfaces with photoelectric isolation is designed.The DSP’s port UART0 maps to the RS422 port of FCC through FPGA,which is used for communicating with C6747.The UART1 and UART2 map to IMU and GNSS receiver respectively for getting measurement information.There are also two serial ports expanded by FPGA: a RS232 monitoring port and a RS422 debug port for backup.In addition,we design a composite interruption.By reading the GPIO bank4 and bank5 interrupt status register,we realize the centralized treatment of GNSS receiver’s second pulse signal and expanded serial port interruptions.This greatly reduces the difficulties of configuring and programming for hardware driver.The Fig.2 shows the overall structure of hardware in this system.

Fig.2 Overall structure of hardware

2 Algorithm design

For PGB,its work time is quite short(usually less than 10 min); At the same time,taking the requirements of providing enough time margin for the implementation of guidance and control into consideration,the scale factor error and slow drift of gyroscope and accelerometer can be ignored.

As stated previously,we construct the mathematical model of SINS/GNSS integrated navigation system based on combination of velocity/position,using adaptive Kalman filter for information fusion meanwhile.After the IMU and GNSS receiver output original measurement information,we can provide aerial time-critical guided bomb with accurate real-time navigation information by utilizing the time synchronization method of 1PPS second pulse signal and integrated navigation software solution.

2.1 State and measurement equation

The discrete state equation of system is defined as:

Where,Φk|k-1is system transition matrix,Γk-1andWk-1are system noise driving matrix and system zero-mean white noise vector,Xkis system state vector,respectively.Xktakes the following form:

Where,ψE,ψN,ψUare misalignment angles of navigation platform,δVE,δVN,δVUare velocity errors,and δL,δλ,δHare position errors,respectively.Here,theεx,εy,εzare constant gyro drift and the▽x,▽y,▽zare constant accelerometer offsets.

The measurement equation of system is taken to be:

Where,Zkis observation vector,Hkis observation matrix andVkis observation zero-mean white noise vector,respectively.

2.2 Adaptive Kalman filter

Fading Kalman filter has been used for PGB and the equation is as follows:

Where,λis fading factor.The filtering gain is enlarged through introducingλ; It enhances the correction function of new measured information.As a result,filtering divergence can be prevented effectively.Here are the calculation formulas ofλ:

3 Test and verification

3.1 Hardware-in-loop simulation scheme design

Compared with single digital simulation,the hardware-in-loop simulation (HILS) is a kind of low-cost and important experimental technique,in which virtual and real objects are all in the loop.It can reflect not only static but also dynamic characteristics of system and is much closer to real conditions[7-8].

In order to verify the performance of integrated navigation system and the strike accuracy against dynamic/static target,a HILS scheme without three-axis revolving table is proposed in this paper.The hardware devices of simulation contain following four parts: PGB trajectory simulation computer(TSC),integrated navigation system,missile-borne flight control computer and monitoring computer.The process of HILS is presented in Fig.3.

Fig.3 Flowchart of hardware-in-loop simulation

In the HILS,data exchange among subsystems makes a closed ring by multi-channel serial communication; we realize RT and non-RT simulation which is based on step timing control and treat the 2.5 ms feedback rudder command as time primary standard.The process of simulation test is given in detail as following steps:

1) Initial parameters binding of trajectory simulation.The parameters included are strike target type,missile firing range and parameters related to missile frame at the moment of releasing bomb.It enters the handshake stage after binding.

2) Handshake stage among subsystems.The beginning of handshake stage is equivalent to entering the stage of preparation for releasing PGB.Firstly,handshake signal 1 and 2 are sent to TSC from NC and FCC.This indicates that system self-inspection is completed.Upon that,the integrated navigation system receivespackets of initial parameters from TSC and extracts initial alignment information from them; It also transfers data packet 3 which contains information of target and range to FCC for initializing the target simulation module at the same time.Finally,the FCC returns a signal to TSC as the end of handshake stage.The navigation,guidance and control stage is about to start.

3) Stage of navigation、guidance and control.This phase includes the entire flight process from releasing PGB to hitting the target.There are four key tasks in this phase: target motion simulation,flight trajectory calculation,integrated navigation calculation and guidancecontrol calculation.

3.2 Simulation result

Based on the design of scheme that given previously,an experiment is performed to test the strike accuracy against low-speed maneuvering target with S-shaped path (|Vt|≤20 m/s).The whole process is under the effect of random wind (|Vw|≤14 m/s); GNSS signal is set to be invalid during following time:1～5 s,130～150 s,220～230 s,280～290 s; The initial parameters of kalman filter are set as:

Trajectories of PGB and target are shown in Fig.4,and curves of navigation error is presented in Fig.5～7.

Fig.4 Trajectories of bomb and target

Fig.5 Curves of position errors

Fig.6 Curves of velocity errors

Fig.7 Curves of attitude errors

Results and analysis:

1) The algorithm time-consuming tests show that SINS algorithm costs 90 μs and kalman filtering costs about 2.1 ms; Besides,whole flight time is 301 s,the communication rate of each serial COM port is 115200bps and the average packet drop rate is lower than 0.01‰.These indicate the hardware has real-time performance and high reliability.

2) The Fig.5～7 show that the SINS/GNSS integrated navigation system can effectively track the position,velocity and attitude of PGB,where the horizontal and vertical position errors are ≤2 m and ≤5 m,respecttively.The velocity error is ≤0.1 m/s,attitude error is≤0.1° and the final hit accuracy of PGB is less than 2 m.

3) The navigation system can still keep high accuracy when GNSS signal is invalid.It proves that theSINS/GNSS integrated navigation system designed is able to provide accurate and reliable process guidance to the aerial time-critical guided bomb.

3.3 Ground test

The test is carried out in a section near the Jiangning development area in Nanjing.The GNSS signal is interfered or invalid at times.The Fig.8 shows the trajectory of test.

Fig.8 Trajectory of ground test

In case that there is no attitude reference for comparison,we take the outputting position and velocity of GNSS receiver which has good precision in normal working condition as primary standard to test the performance of system in real circumstances.The horizontal positioning error of static test is shown in Fig.9 and dynamic testing result is in Table.1.

Fig.9 Horizontal positioning error of static test

Tab.1 Dynamic testing result

Results reveal that the static horizontal position error is ≤1 m.In dynamic situation,the velocity error is almost less than 0.1m/s,position error is ≤3 m,respectively and the precision can satisfy the requirements of performance.

4 Conclusion

The hardware design of SINS/GNSS integrated navigation system for aerial time-critical guided bomb is introduced in detail and the algorithm is designed in this paper.A hardware-in-loop simulation (HILS) scheme without three-axis revolving table is proposed.Through the simulation and ground test,the strike accuracy against dynamic/static target is verified.The precision of SINS/GNSS integrated navigation system can fulfill the requirements of precision strike..

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1005-6734(2014)02-0195-05

航空時敏炸彈SINS/GNSS組合導航系統(tǒng)設計

陳 帥，雷浩然，薄煜明，徐芹麗
（南京理工大學 自動化學院，南京210094）

為滿足機載精確制導彈藥小型化、高可靠性方面的要求，設計了一體化閉環(huán)光纖慣導/GNSS緊湊型組合導航系統(tǒng)，該樣機基于DSP C6747+FPGA淺并行架構，運用自適應卡爾曼濾波算法實現(xiàn)組合導航系統(tǒng)的信息融合，樣機整體尺寸為13 cm×14 cm×12 cm。為驗證系統(tǒng)性能，搭建了彈載組合導航半實物仿真平臺，通過計算機仿真模擬目標信息和炸彈飛行全過程，分析了在組合導航系統(tǒng)輔助下制導炸彈對目標的打擊精度，最后對樣機進行了地面跑車試驗的考核。半實物仿真與地面跑車試驗結果表明，該組合導航系統(tǒng)具有較好的實時性和穩(wěn)定性，導航精度滿足精確打擊的要求。

組合導航系統(tǒng)；卡爾曼濾波；制導炸彈；半實物仿真

V249.3

：A

2013-10-16；

：2014-01-29

國家自然科學基金委員會和中國工程物理研究院聯(lián)合基金資助（U1330133）；江蘇省自然科學基金（BK20130774）

陳帥（1980—），男，博士，講師，碩士生導師，研究方向為組合導航。E-mail：c1492@163.com

10.13695/j.cnki.12-1222/o3.2014.02.010