Nodding LIDAR For Applied Research Associates By Roscoe Kane and John Barton.

Nodding LIDARNodding LIDARFor Applied Research AssociatesFor Applied Research Associates

By Roscoe Kane and John BartonBy Roscoe Kane and John Barton

OverviewOverview

BackgroundBackground SolutionSolution DesignDesign SoftwareSoftware Project ManagementProject Management

BackgroundBackground

LIDAR stands for LIDAR stands for LiLight ght DDetection etection AAnd nd RRanginganging

Emits a pulsed laser beam and Emits a pulsed laser beam and measures the time between measures the time between emission and return to determine emission and return to determine distancedistance

Most systems are at best 2 Most systems are at best 2 dimensional, with 1 axis of sweep dimensional, with 1 axis of sweep that returns 1 dimension of rangethat returns 1 dimension of range

Problem StatementProblem Statement

Develop a system to adapt a 2 dimensional Develop a system to adapt a 2 dimensional LIDAR system into a 3 dimensional LIDAR LIDAR system into a 3 dimensional LIDAR system by adding a second axis of rotationsystem by adding a second axis of rotation

Do this by nodding the system up and down in Do this by nodding the system up and down in a sinusoidal patterna sinusoidal pattern

SpecsSpecs

30º minimum sweep angle30º minimum sweep angle .5hz minimum scan rate.5hz minimum scan rate Capable of any orientationCapable of any orientation Capable of being disabledCapable of being disabled Safety for both humans and robotSafety for both humans and robot Bolts to table for displayBolts to table for display

SpecsSpecs

Up 30 deg. In ≤ 1 secDown 30 deg. In ≤ 1 sec

Bolts for mount to table

Works if mounted in any orientation

Our SolutionOur Solution

Move the entire system about it’s center of Move the entire system about it’s center of gravitygravity

Use a resonant spring oscillator to generate Use a resonant spring oscillator to generate an constant frequency and allow for a an constant frequency and allow for a smaller motorsmaller motor

Use a Maxon motor and motor controller to Use a Maxon motor and motor controller to start, stop and maintain oscillationstart, stop and maintain oscillation

Axis of Scan

Axis of Sweep

More then 30 scans per sweepSweep is primary axis

Movement of LIDAR Unit

System DiagramSystem Diagram

Motor Controller

Motor

Encoder

Data Flow

Mechanical Drive

24V Power Supply

Power Flow

PC

Spring

LIDAR

Mechanical DesignMechanical Design

The LIDAR bracket The LIDAR bracket mounts the LIDAR mounts the LIDAR system and rotates system and rotates with it.with it.

The base holds the The base holds the bracket up and serves bracket up and serves as a referenced for as a referenced for both the motor and both the motor and spring to act on.spring to act on.

Spring SizingSpring Sizing

• The model for our mechanical system is The model for our mechanical system is shown below, where the arrow shows our shown below, where the arrow shows our motor inputmotor input

• The size of the spring affects the natural The size of the spring affects the natural frequency of the systemfrequency of the system

Spring SizingSpring Sizing

There are many ways to design a spring for a There are many ways to design a spring for a systemsystem

We tried first calculating the spring constant, but We tried first calculating the spring constant, but were unable to purchase a spring using that valuewere unable to purchase a spring using that value

Next we tried calculating the physical size of the Next we tried calculating the physical size of the spring, but were unable to get a plausible value spring, but were unable to get a plausible value from any available spring sizing calculationsfrom any available spring sizing calculations

Finally, we simply ordered a few springs that Finally, we simply ordered a few springs that should add up to approximately the spring should add up to approximately the spring constant we needconstant we need

This way we can add or remove springs to adjust This way we can add or remove springs to adjust the spring constant, and subsequently the natural the spring constant, and subsequently the natural frequency frequency

Software DevelopmentSoftware Development

The programming was made much easier The programming was made much easier because the motor controller came with a because the motor controller came with a DLL of functions that control position, DLL of functions that control position, velocity and acceleration very simplyvelocity and acceleration very simply

The functions can also control velocity and The functions can also control velocity and position in a profile, either trapezoidal or position in a profile, either trapezoidal or sinusoidalsinusoidal

Functions in a DLLFunctions in a DLL

The functions to control our motor are The functions to control our motor are inside a managed DLLinside a managed DLL

The code to use functions inside a DLL The code to use functions inside a DLL was difficult to findwas difficult to find

Main LoopMain Loop

Data CorrelationData Correlation

Motor encoder data is time stamped and Motor encoder data is time stamped and savedsaved

LIDAR data is given correlated with the LIDAR data is given correlated with the encoder data based on the timestampencoder data based on the timestamp

BudgetBudgetItem Price Quantity Cost Status Distributor Distributor ID

motor with encoder $200 1 $200 on hand Maxon

spring $6.00 6 $36 need McMaster 9271K124motor controller $5 1 $5 on hand Maxon HCS08 $2 1 $2 on hand Mouser

.5" Aluminum Plate $55 .5ft x 3ft $55 need McMaster 8975K221

.25" Aluminum Plate $25 1 ft^2 $25 in shopDiscountSteel.com

3/4" Aluminum Rod $10 36' $10 need McMaster 8974K113

bearings $39 2 $79 need McMaster 6357K358/32X3/1" Slotted Machine Screws $7 2 $14 need McMaster 98164A143

Angle Aluminum $253ft $100need McMaster 88805K49

total $526

total cost to us $294

Workload DistributionWorkload Distribution