Research on Mechanical Moving Components for Space Use

19th Microelectronics WorkshopOctober 25-27, 2006 Tsukuba, Ibaraki, JAPAN

Shingo OBARAElectronic, Mechanical Components and Material Group

Institute of Aerospace TechnologyJAXA

Activities in mechanical components sub-group

- Outline- Development of mechanical

moving components- Project support

Activities in Mechanical Components Subgroup (1/2)

Electronic, Mechanical Components and Material Group

- Development of selected moving mechanical components (MMCs)

- Research on generic technology for space mechanisms

- Standardization activity for space mechanisms

- Project support

Mechanical components sub-group

High Vacuum Mechanical Component Test Facilities

Electronic components su-bgroup

Material sub-group

Activities in Mechanical Components Sub-group (2/2)

Fluid (oil & grease) lubrication

Solid lubrication

Bearings Gears Sliding electrical contacts

High accuracy positioning and sensing

Long life

Applicable to all advanced space mechanisms

High agilityRequirements

Resolver

Harmonic drive gear

Slip-ring

Low shock hold-down& release mechanism

Technical trends of space mechanisms and satellite

Year 2005 2010

2nd phase1st phaseDevelopment of high-priority MMCs

Research on Generic technology:Space tribology

For high reliabilityDocumentation &Standardization Design guideline, Handbooks, Standards

Development of selected MMCsDevelopment: 1st phase (2003～）(1) Resolver

(Angular sensor)- High accuracy

< ±0.0015°- High resolution

21 bit

(2) Harmonicdrive gear

- Light weight & compact

- Long life> 106 rev.

Committee on Space Component Technology,Space Mechanical Components & Materials SubcommitteeSelection of high-priority MMCs-For solving availability problem

-To obtain higher performance

-For growing the market

Project SupportPerformance

verification testFailure analysis

SEM observation of fracture surfaces of H-II LE-7 engineLife evaluation test of ball bearings

for GOSAT satellite

Failed FTP inducer

Starting point of fatigue fracture

Research on space tribology

- Fluid lubrication- Solid lubrication

Fluid (oil & grease) lubrication

Tribological characteristics of existing fluid lubricants- Wear and friction coefficients

- Effect of additives

High-priority MMC related research- Lubrication mechanism of harmonic drive gears

Lubrication mechanism of ball bearings- In-situ measurement of film thickness- Tribological characteristics of oil-impregnated retainer

- Life tests

- To establish fluid-lubricating method for space applications

- To accumulate technical data of mechanical components

Ball bearing dynamics simulation - Effect of gravity on bearing performance

- Retainer instability

Collaborated with universities, companies and JAXA advanced space technology research group

Fluid lubricants・ＭＡＣ (+additives)・ＭＡＣ based grease・PFPE

Feasibility of new lubricants- Tribological characteristics

To be presented

Solid lubricationSolid lubricants・MoS2・Gold alloy・DLC

Effect of environment & operating conditions- Long term storage in atmosphere (non-operative)

- Vibration & operating mode (small angle rotation, linearreciprocal motion, etc.)

High-priority MMC related research- Feasibility tests of friction materials for slip-ringsGuidelines of solid lubrication

for space applications- Use in harsh environment (fluid lubr. cannot be used)- Life limitations (sensitive to operating conditions)

Feasibility for space applications- Existing, high-performance non-space lubricants

- New lubricants

Advanced lubricant and/or lubricating method for future missions- Long life solid lubrication- Extremely low friction

Collaborated with universities, companies and JAXA advanced space technology research group

To be presented

Tribological characteristics of space oils－Collaboration with Tokyo Institute of Technology (TIT)－

0

2

4

6

in air invacuum

in air invacuum

in air invacuum

MAC MAC+TCP PFPE TYPE Fz

Wea

r R

ate

, ×10

-10 m

m2

SUS440C-ball/ SUS440C-diskSliding speed: 11.2mm/sLoad: 100NDuration: 60min

Wear test results for space oils

Ball surfaces after the wear tests

* Friction and wear character-istics of promising oils for space use have been evaluated with a pin-on-disk tribometer.- MAC- PAO- PFPE- Mineral oil

* Effectiveness of inclusion of extreme-pressure additives and/or anti-oxidants in hydro-carbon oils is investigated.- TCP- Hindered phenols- Amines

MAC MAC+TCP PFPE TYPE Fz

In-situ measurement of oil film thickness on ball bearing raceway

－Collaboration with TIT－* Downsized, high-resolution Laser Induced Fluorescence (LIF) system was

developed for measuring oil film thickness during ball-bearing operation.* The film thickness on the raceway was decreased by repeated ball

passings, and finally, a submicron scale thin film was left, contributing to hydrodynamic lubrication of the bearing.

Oil with fluorescer

Condenser lens

Filter

Photomultiplier tube（PMT）

Outer-raceway of ball bearing

Ball

Light source(Laser diode)

Exci

tatio

n lig

ht 4

42nm

Fluoresce

nce 50

0nm

Oil with fluorescer

Condenser lens

Filter

Photomultiplier tube（PMT）

Outer-raceway of ball bearing

BallBall

Light source(Laser diode)

Exci

tatio

n lig

ht 4

42nm

Fluoresce

nce 50

0nm

0

100

200

300

400

500

0 20 40 60 80Running time [min]

Oil

film

thic

knes

s [n

m]

40mm-bore sized ball bearing at 500r/min

Ballbearing

Result of film thickness measurementIn-situ measurement system using LIF

Ball bearing dynamics simulationDynamic analysis code of ball bearings has been developed

– for understanding the effect of gravity condition on bearing performance, and

– for rapid evaluation of key bearing design factors.

0 1

0゜

90゜

180゜

270゜

Effect of gravity condition on retainer motion.(Mass centre loci of gyroscope bearing retainer at 9000 r/min)

Horizontal shaft in 1g

0 1

0゜

90゜

180゜

270゜0 1

0゜

90゜

180゜

270゜

Vertical shaft in 1g 0 g

3-D animation of unstable retainer motion. （Gyroscope bearing at 9000 r/min. The retainer motion is exaggerated.）

Generally, life of Harmonic Drive Gears (HDGs) in vacuum is remarkably shorter than that in air. Why ?

Time, s

Load

torq

ue

13 N・m

CW CCW

(a) In vacuum

0

50

Mea

sure

d vo

ltage

betw

een

WG

/FS,

mV

(Contact)

(Non contact)

0 50

Time, s (b) In air

0

50

Mea

sure

d vo

ltage

betw

een

WG

/FS,

mV

(Contact)

0 50

(Non contact)

Measurement of voltage E between WG and FS

E

Flexspline

Wave-Generator

Harmonic Drive Gear

Electric resistance measurement among HDG elements

This is probably because the lubricant between Wave Generator (WG) and Flexspline (FS) is rapidly starved when HDG is operated in vacuum.

Lubrication mechanism of Harmonic Drive Gears

Measured voltage E(MAC-based grease, input rotational speed: 200 rpm)

Long life solid lubrication of ball bearings by tribo-coating－Collaboration with Tohoku University－

Ball bearing

Shaft

5mm

Micro Evaporation Source Arrayproduced by MEMS technology

Heater

Solid lubricant (Indium)

Insulating film

Cross sectional view

Applicability of advanced solid lubricating method called “tribo-coating” to ball bearingsis investigated.

Tribo-coating: - Periodic resupply of a solid

lubricant to sliding surface by evaporation.

- Long lifetime over 107

revolutions and low friction coefficient under 0.02 were achieved in pin-on-disk experiments. Tribo-coating lubrication system

for ball bearing

SummaryActivities for moving mechanical components- Development of selected moving mechanical components- Research on space tribology- Providing handbooks, guidelines and standards for spacemechanisms

Space tribology research- Key technology to develop future space mechanisms with

high performance and high reliability.- Continuing effort to gather technological data and to get

perspective of phenomena involved.