Development of Mine Detection Development of Mine Detection SystemSystem

Jim SellersJim Sellers

Mechatronics Systems Engineering Mechatronics Systems Engineering ConsultantConsultant

8-10 December 20148-10 December 2014

International Summit on Industrial EngineeringInternational Summit on Industrial Engineering

San Francisco, CA USASan Francisco, CA USA

AbstractAbstract

Land mines have been used extensively in worldwide Land mines have been used extensively in worldwide conflicts for many years, and have killed and maimed conflicts for many years, and have killed and maimed an untold number of warriors and civilians. These an untold number of warriors and civilians. These explosives remain buried long after the hostilities end explosives remain buried long after the hostilities end and still wreak havoc on unsuspecting citizenry going and still wreak havoc on unsuspecting citizenry going about their normal lives. An international outcry about their normal lives. An international outcry regarding these dangers resulted in efforts to end regarding these dangers resulted in efforts to end their use and to rid known mined areas of these their use and to rid known mined areas of these dangers. This presentation discusses the development dangers. This presentation discusses the development of a mine detection system mounted aboard a of a mine detection system mounted aboard a helicopter and the statistical analyses involved in that helicopter and the statistical analyses involved in that effort.effort. 

IntroductionIntroduction

• Proof of concept program only.Proof of concept program only.– Requirements are typical but not specific.Requirements are typical but not specific.

• Helicopter-mounted turret laser scanner.Helicopter-mounted turret laser scanner.

• Want to scan certain area of ground with Want to scan certain area of ground with laser to assist in detecting mines.laser to assist in detecting mines.– Very politically-charged topic for many years.Very politically-charged topic for many years.

Typical Stabilized TurretTypical Stabilized Turret

System OperationSystem Operation• Dual-mode: coarse/vernierDual-mode: coarse/vernier

– Coarse: Two-axis gimbal provided by consultant.Coarse: Two-axis gimbal provided by consultant.– Vernier: provided by azimuth and elevation fast steering Vernier: provided by azimuth and elevation fast steering

mirrors (FSM) located on gimbal inner platform.mirrors (FSM) located on gimbal inner platform.

• Combination of maximum specified helicopter Combination of maximum specified helicopter height and detector array configuration yielded height and detector array configuration yielded the conversion that one pixel size equals a certain the conversion that one pixel size equals a certain distance of ground distance (83 microradian distance of ground distance (83 microradian maximum subtended angle).maximum subtended angle).– Sets total line-of-sight (LOS) pointing requirement.Sets total line-of-sight (LOS) pointing requirement.

• As helicopter flies, combination of gimbal and As helicopter flies, combination of gimbal and FSMs produces raster scan utilizing FSMs produces raster scan utilizing Velocity/Altitude tracking to completely scan a Velocity/Altitude tracking to completely scan a certain area of ground in a repetitive stare-step-certain area of ground in a repetitive stare-step-stare manner.stare manner.

System OperationSystem Operation

• For raster scan, requirement was to align For raster scan, requirement was to align within one pixel at the beginning of each within one pixel at the beginning of each raster segment origin.raster segment origin.– Pointing accuracy requirement of 83 Pointing accuracy requirement of 83

microradians.microradians.

• During stare (dwell), one-half pixel size During stare (dwell), one-half pixel size smear requirement was imposed.smear requirement was imposed.– Pointing stability requirement was 41.5 Pointing stability requirement was 41.5

microradians RMS.microradians RMS.

• Pointing stability requirement sets total Pointing stability requirement sets total LOS requirement.LOS requirement.

System Operation AnalysisSystem Operation Analysis• Coarse turret provider specification: 16 Coarse turret provider specification: 16

microradian RMS pointing stability at the microradian RMS pointing stability at the inner platform of the turret.inner platform of the turret.– LOS requirement imposed on combination of LOS requirement imposed on combination of

azimuth and elevation FSMs is 33 microradians azimuth and elevation FSMs is 33 microradians RMS.RMS.

• Looked for alternative approaches.Looked for alternative approaches.– Showed by analysis that IF we could relax the Showed by analysis that IF we could relax the

helicopter forward velocity requirement by helicopter forward velocity requirement by 15%, and IF we could use a slightly different 15%, and IF we could use a slightly different ground coverage pattern, we could eliminate ground coverage pattern, we could eliminate the elevation FSM entirely (even under worst-the elevation FSM entirely (even under worst-case crab angles).case crab angles).

System Operation AnalysisSystem Operation Analysis

• Customer tentatively accepted this solution, Customer tentatively accepted this solution, meaning that azimuth FSM LOS pointing stability meaning that azimuth FSM LOS pointing stability requirement is 33 urad RMSrequirement is 33 urad RMS– Instead of V/H tracking-based raster scan, we now plan Instead of V/H tracking-based raster scan, we now plan

to use “broomsweep” pattern with flyback.to use “broomsweep” pattern with flyback.– Since the azimuth FSM LOS experiences angular Since the azimuth FSM LOS experiences angular

doubling, the azimuth FSM pointing stability doubling, the azimuth FSM pointing stability requirement is 16.5 urad RMS.requirement is 16.5 urad RMS.

• Static error budget analysis and detailed Static error budget analysis and detailed Matlab/Simulink model was used to show that we Matlab/Simulink model was used to show that we could indeed meet this requirement with a very could indeed meet this requirement with a very accurate absolute digital encoder as long as we accurate absolute digital encoder as long as we could drop several of the encoder LSBs during could drop several of the encoder LSBs during flyback.flyback.

System Test and IntegrationSystem Test and Integration

• Worked with mechanical, software, and Worked with mechanical, software, and electronics teammates to successfully electronics teammates to successfully build mirror, discretize control laws build mirror, discretize control laws (including FSM bending mode (including FSM bending mode compensation), and to bench test the compensation), and to bench test the azimuth FSM.azimuth FSM.– FSM worked correctly as predicted by my FSM worked correctly as predicted by my

simulations.simulations.

• End-item customer was very satisfied End-item customer was very satisfied with proof-of-concept results.with proof-of-concept results.

SummarySummary• Carefully assess the requirements imposed Carefully assess the requirements imposed

on a system. Challenge when prudent to on a system. Challenge when prudent to do so.do so.

• Ensure that analysis and simulation results Ensure that analysis and simulation results make sense with regard to the physical make sense with regard to the physical limits of the real-world system.limits of the real-world system.

• Make sure that error analysis and Make sure that error analysis and subsequent budgeting are realistic.subsequent budgeting are realistic.

• Don’t “reinvent the wheel” if an existing Don’t “reinvent the wheel” if an existing similar system has done similar analyses, similar system has done similar analyses, simulations, and testing. Leverage their simulations, and testing. Leverage their work efforts and correlate if possible.work efforts and correlate if possible.