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StepSPACE ROBOTICS INITIATIVESkyworker CDR 11/18/99-1

Skyworker - Mobile ManipulatorCritical Design Review

Field Robotics Center

November 18, 1999

William Red WhittakerPeter StaritzChris Urmson


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Constellation of SSPsatellites in GEO

1GW of energy to theground

Microwave transmissionantenna 1 km in diameter

Mass of 4800 MT (10X asmassive as ISS)

Assembled over 1 year,maintained for 30 years

Space Solar Power (SSP) Facilities

4000 m


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Assembly, Inspection, Maintenance

Extremely large scale structures

Poor accessibility

Long life cycle

Dangerous environment

Necessitates a robotic workforce Assembly, Inspection, Maintenance (AIM)

Radiator

Parabolic Reflector

Radi

atorParabolic Reflector


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Objectives

Demonstrate the viability of using robots for orbital

construction Prove the validity of using structure walkers for orbital

AIM

Demonstrate SSP AIM relevant tasks using robotics

Simulate prospective SSP AIM robots and tasks


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Representative Tasks

Walk, turn, and transition across planes on a truss

structure Pick up and place a payload at arbitrary locations and

orientations in space

Carry a payload while walking, turning, and

transitioning Conduct calibration and inspection tasks

Connect power and communications cables

Cooperatively carry massive or large payloads

Perform tasks that require multiple robot collaboration


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Demonstration

Prototype Robot

Pick up and carry a model transmitting element the length of thetruss, turn while carrying, couple the element to the structure

Connect Power Management and Distribution (PMAD) to theelement

Perform a mock calibration

Simulation Large scale construction utilizing multiple robots

Coordinated installation of full scale transmitting elements

Demonstrate extended lifetime operations


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Configuration - Key Metrics

Continuous Gait Forces exerted / Forces experienced

Workspace

Control Complexity

DOF

Mass

Cost

Energy Consumption


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Skyworker

Continuous Gait Reduced forces on

structure

Low energyconsumption

Constant contact withstructure

Requires 4 jointsynchrony

11 Degrees of freedom

Extensive Workspace


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Skyworker - Specifications

Tetherless Mobile Manipulator

Processor: Pentium166

Walking Speed: 10cm/s

Mass:


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Force Analysis

Mass Estimates

Forces Due to imperfectGC system

Maximum torque 16 N-m

Maximum force 12N

Mass Quantity Group Mass

Joints 2 kg 11 22 kg

Links 4.5 kg 3 13.5 kg

Grippers 3.0 kg 3 9 kg

Total 44.5 kg

Original Mass Estimates


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Joint Development

Determined maximumtorque, speed, andtravel needed for gait

Modularityconsiderations

Motor / ReductionCombination 16 Nm torque +

44 degrees/second +

Skyworker actuators 57.5 degrees/second at

32 Nm torque

Joint Required Max Torque Required Max Speed Max Theta1 16 Nm 32.1 deg/s +/- 180 deg

2 Variable Variable +/- 90 deg3 Variable Variable +/- 90 deg4 Variable Variable +/- 90 deg5 10 Nm 43.2 deg/s +/- 180 deg

6 Variable Variable +/- 90 deg7 1 Nm 32.7 deg/s +/- 180 deg8 9 Nm 35.1 deg/s +/- 180 deg9 Variable Variable +/- 90 deg

10 Variable Variable +/- 90 deg11 Variable 35.1 deg/s +/- 180 deg

62.5 degrees/second at16 Nm torque


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Reduction

Two Stage Transmission

Stage 1 - Planetary Gearhead Integral Unit

4.8 to 1 reduction

1.3 deg no-load backlash

80% efficiency Stage 2 - Harmonic Drive

High reduction ratio with zerobacklash

Low mass - high torque ratio

Efficiencies ranging from 70% to80%

Ratio 100 to 1

Rated torque at 2000 rpm 7.8 Nm

Rated average torque 11 Nm

Limited repeated peak 28 Nm

Limit momentary peak 54 Nm

Maximum Input Speed 5000 rpm

Average Input Speed 3500 rpm

Mass .09 kg

CSF 2A-GR-14Harmonic Drive


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Motor Selection

Motors Selection Criteria

Power Minimization Mass

Available with integral encoderand planetary gearhead

Space relevance

Maxon Motors DC Graphite Brushed

Rated for 42 volts, operating at

30 volts .340 kg

4800 rpm & 24 Nm outputtorque requires 48 watts


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Joint Overview

3 Inline revolute (Size A)

2 Offset (Cantilever) revolute 3 Inline revolute (Size B)

3 Axial revolute


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Axial Revolute Joint

Most

Complicated

Interfacebetween F/Tsensor and

Gripper

Mass 1.48 kg

Shear key


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Anatomy of a Joint

Force Torque Interface Cap

Force Torque Interface

Bearing Secure

Bearings

Output Shaft

Harmonic Housing

Harmonic Drive

Potentiometer Belt

Feedback Drum

Bearing Baseplate

Gripper Interface

Force Torque Closing Plate

Potentiometer Pulley

Potentiometer

Motor/Planetary/

Encoder Package


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Structure Overview

High bending and

torsional stiffness

Weight minimization Truss reduction

Access via removablebottom plates Also serve as internal

attachment points

Each link is unique Little opportunity for

modularity


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Gripper


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Grippers Force Analysis

Clamping forceneeded to counteract

effects of stride

Maximum forcerequired: 500N

x

y

z

Time (s)

Time (s)

Force

(N)

Force(N

)

Singularity in stride


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Concept

Dynamic gait requires a robust andfast gripping mechanism

Robustness

Simple Design - Single jaw actuated

Low Power - Limited motor torquerequired

Error Correction - Designed with

mechanical allowance for imperfectapproach

Speed

Fast Approach - Direct approach allowedby configuration

Fast Mechanism - High speedadvantage provided by linkage

Fast Motor - High RPM attained with lowtorque requirement


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Mechanism

Gripping Mechanism: Vise Grip

Four bar linkage

Speed Advantage: Moving jawadequately slowed at final closing

Force Advantage: Motor force

multiplied at locking Power Advantage: Zero power

required when locked


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Coating

Potential for wear of

aluminum gripping facemandated protectivecoating

Stainless Steel Coating

Reduced wear Increased coefficient of

friction

Thermally sprayed coating

courtesy of the StateUniversity of New York atStony Brooks Center for

Thermal Spray Research


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Gravity Compensation

Skyworker requires gravity

compensation to operate properly

Marionette style cable supportcounteracts the force of gravity

Combination Active/Passivesystem Vertical axis is passive

Horizontal axis are active

Modify a heritage gravity

compensation system


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Robot Interface Modifications

Four attachmentpoints

Sliding interface toallow transition

between walkingand manipulatingpostures

Arc center located

at CG


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Feedback Controller

Optical Angle Sensor

Picture of shuttle withangle sensor board

(to be taken w/ digital camera)

Output voltages linear function of angles.


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Feedback Controller

Control Issues

Gantry pendulum is a fourth order system

Model as a second order system Second order model sufficiently accurate over a small range of

inputs.

Skyworker will only move over a small range of velocities.

Tune PID controller for good responses over these inputs.

Hack: Zero integral term with change of direction (fasterresponse)


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Skyworker: Power Electronics

Power Budget: Motors: 140W peak power required

Motor controllers, communications, sensors, digitalelectronics, CPU, and miscellaneous: +5, +10, -10 voltsupplies, 60W maximum

Worst case: 200W Mass Constraint: 4kg (batteries+converters)

Skyworker must be capable of performing operationsfor a minimum of 20 minutes prior to recharging


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Battery Technologies

Batteries we considered:

New high-rate discharge NiMH batteries will be used, because

they provide a high power/weight ratio along with other desirableproperties

NiCd NiMH New NiMH Li-Ion

Energy/kg Fair Good Good Excellent

Energy/cm3

Fair Good Good Excellent

Charge Rate High Moderate High Low

Ease of Charging Easy Easy Easy Difficult

Max. Discharge Rate

(Power)

High Moderate High Low

Cost/W Low Low Low HighMass/W Low Moderate Low High

Volume/W Moderate Moderate Moderate High


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Panasonic High Rate Discharge NiMH

Cell size Sub C

Mass per cell 55g

Cell voltage 1.25V down to 1V during discharge

Current 3000mA-hours

8 to 9 amps continuously for 20 minute demo

3.4 usable watt-hours per cellCharge rate 1 hour quick charge with delta-V charger

(Standard NiCd battery charger)

Max discharge rate 10 Amps (10 Watts/cell minimum)

Other nice features No memory effect

500 charge/discharge cycles

Comparison to NiCd Equal or better in every way to NiCd, with twice the energy

density of NiCd and (amazingly) no more expensive


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Power System

Two separate battery packs

Motor pack 30 cells

102 watt-hours

Electronics pack

20 cells

68 watt-hours Further optimization possible (to equalize run time)

Powers three switching power supplies that produce +5V, +10Vand10V

Safety System E-stop switches located on robot and at control station

Power switching circuitry prevents simultaneous connectionof multiple power sources


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Testing Batteries


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StepSPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-32

Battery and Tethered Operation

Charging

Using external delta-V chargers to charge batteries withoutremoving them from Skyworker

Battery Monitoring System Battery voltage monitoring circuitry will let Skyworker know

that its batteries are nearly drained

When Skyworkers batteries are recharging, it can

run off of a tether that supplies 36V and 24V toSkyworkers motors and voltage regulators.


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StepSPACE ROBOTICS INITIATIVE Skyworker CDR 11/18/99-33

Electrical Wiring Diagram

A/D

P

A/D

MC MC

MC

MC

MC

MC

MC

MCMC

MC

MC

MC

DC/DC5V

DC/DC10V

DC/DC-10V

A/D

MC MC

SC

SCSC

SC

30V BATT 24V BATT

FT

FT

FT

Legend:

+24V Power-10V Power+10V Power+36V PowerRS232 BusSensor BusData Bus A/DData Bus 1Data Bus 2Data Bus 3

S


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StepSPACE ROBOTICS INITIATIVE Sk k CDR 11/18/99 34

Joint Labeling Scheme

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