© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011

Automatic Battery Replacement System for UAVs:

Koji A.O. Suzuki, Paulo Kemper and James R. Morrison

KAIST (Korea Advanced Institute of Science and Technology), South Korea

Complex Stochastic and Service System Design Lab

http://xS3D.kaist.edu

Analysis and Design

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 2

Presentation Outline

• Motivation

• Prior art

• Petri net models: Recharge vs. replacement

• Battery replacement system design

• Concluding remarks

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 3

Brief Overview

• Automated battery replacement platforms for UAVs

• Comparison of different solutions for various modules

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 4

Motivation

• Full autonomy requires automation of ground tasks

Ammunition

Pesticides

Batteries

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 5

Motivation

• Possible application KAIST security system

Sentinel

in the

Sky

Full autonomy requires automation of ground tasks

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 6

Problem Statement

• Automate the human based replenishment process

• Focus on energy reservoir: Battery replacement service platform

• Targeted UAVs: E-SKY’s LAMA V3 and HONEY BEE KING II

http://www.twf-sz.com/english/products.asp?prodid=0330http://www.twf-sz.com/english/products.asp?prodid=0016

GOAL: Replenish UAV consumables without human intervention

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 7

Prior Art (1)

• The MIT Aerospace Controls Laboratory (2007) – 1st automated recharging platform for UAVs

– Developed for a quad rotor UAV

• Square landing platform

• Navigation system dependency

• Landing position dependent

http://hdl.handle.net/1721.1/41541

http://dx.doi.org/10.1117/12.580140

• UCSD and SSCSD* (2004)– Refueling vehicle for ducted fan UAVs

* SSCSD: SPAWAR Systems Center, San Diego

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 8

Prior Art (2)

• University of Michigan (2010) – 1st automated exchanging platform for UAVs

– Designed for a Lama V4 UAV

• Square landing platform

• Navigation system dependency

• Landing position dependent

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5509165&tag=1

http://mobots.epfl.ch/marxbot.html

• EPFL* (2010)– Battery replacement device for land robots

– Robot can perform “hot-swap” (no turn off)

– Robot must align precisely by itself

* EPFL: École Polytechnique Fédérale de Lausanne

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 9

Battery Recharge or Battery Replacement?

• Battery recharge– Idling time

– Requires more UAVs

– More service stations

• Battery replacement– Less idling time

– Higher coverage per platform

– More batteries

• Coverage: Expected number of UAVs in flight at a time

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 10

Petri Net Models – Battery Recharge Platform

• TF : Time flying

• TI : Time idling

• TR : Time to recharge the

battery

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 11

Petri Net Models – Battery Replacement Platform

• TF : Time flying

• TI : Time idling

• TR : Time to replace a battery

• TC : Time to recharge a battery

• Recharge model is a special case– NBAT = NUAV

– TR = battery charge time

– TC = 0

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 12

Petri Net Models – Battery Replacement Platform

• Defining:

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 13

Petri Net Models – Battery Replacement Platform

• According to Ramamoorthy:

• Then:

• The system coverage is:

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 14

Battery Recharge or Battery Replacement?

Recharge

Replacement

• Low coverage Recharge

• High coverage Replace

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 15

Designing a System for Swapping Batteries

• Guiding the UAV to the battery replacement site

• Orienting the UAV in a desired direction

• Locking the UAV position on the station

• UAV-battery connections: extracting and placing a battery in the UAV

• Battery transportation

• Battery array rechargingBattery

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 16

Design Options: UAV Positioning Methods

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 17

Design Options: Skid Changes or Add-ons

• Support UAV's weight and keep the UAV balanced

• Modifications must not affect the payload significantly

• Allow battery removal from the UAV

• Allow UAV to be locked in place for battery to be removed/placed

• Skid geometry must comply with the UAV positioning

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 18

Design Options: Skid Changes or Add-ons – Battery Case

• Secure location for the battery

• Facilitate battery transportation

• Allows easy modifications.

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 19

Design Options: Battery and UAV Connecting System

A battery holding system in a UAV must be• Low weight• Securely hold the battery during flight• Resist small impacts (such as small drops)• Maintain the battery and UAV terminal connections• Allow easy insertion and extraction of the battery when necessary

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 20

Design Options: Battery Capturing System

What is it?

• Method to secure a battery for transportation

• Safely insert and extract batteries from the UAVs

• Prevent the battery from movement in any direction relative to the capture device or “grabber“

Possible designs:

• Mechanical claw – movement guidance, space required

• Servo-assisted magnets – may attract foreign bodies

• Electromagnets – may increase weight of UAV battery case

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 21

Design Options: Battery Capturing System

• UAV reaches specific position and is locked in place

• Ferromagnetic plate attached to bottom of battery case

• Capturing system moves vertically via an elevator

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 22

Design Options: Battery Transport Method and Storing

• Transportation of the depleted battery and case to the swapping site, where a recharged battery can be obtained

• Charger array is required

• Terminal interfaces that can connect the battery case terminals with the charger ones

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 23

Design Options: Elevator Design and Battery Positioning

• Deliver the battery case to the swapping site

• Scissor elevator design – compact size

• Rack and pinion used to move the battery

• Magazine storage

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 24

Orientation Fixing and Extraction Module - Prototype

• Ensures that extracting and inserting a battery will not affect the position and orientation of the landed UAV

• Electromagnet at the center of the plate

• Servo motor actuated arms hold UAV skids

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 25

Battery Swap Module- Prototype

• Rack and pinion system

• Step motor driving the pinion

• Electromagnet placed on one of the ends

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 26

Prototype information

• Battery exchange time estimate: <1min

• Maximum coverage estimate: 15 UAVs in flight

• Minimum number of batteries needed: 103

© 2011 – K. Suzuki, P. Kemper, J. Morrison – ICUAS’11 – May 27, 2011 - 27

Concluding Remarks

• Full automation required automation of ground tasks

– Automated service stations allow fewer humans, reduced risks and increased self-sustained operational time

– Enabling technology for complete autonomy

• The Petri net models useful for system sizing

• Our proposed ground station

– Relieves the burden of pin-point landing (e.g., in adverse weather)

– Performs battery replacement within 1 minute

– Allows a coverage up to 15 UAVs (Honey Bee King II)