A Miniaturised Space Qualified MEMS IMU for Rover...

A Miniaturised Space Qualified MEMS IMU

for Rover Navigation

“Multi Wafer Hybrid Integration: Rover IMU 1”

Presented by John Cornforth and Felix Rehrmann

at 11th Symposium on Advanced Space Technologies in Robotics and Automation

ESTEC 11th – 14th April 2011

2

Overview

• The objective of the Multi Wafer Hybrid Integration:

“Rover IMU I activity is to design and demonstrate an IMU

that can be used for navigation in the context of rover

based exploration missions. The target environments are

Mars and Moon missions.”

• Outline

Introduction

Requirements

Architecture and Miniaturisation

Breadboard

Testing

Conclusion

Multi Wafer Hybrid Integration: Rover IMU 1

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Advanced Space Technologies in Robotics and Automation

3

Partners


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Prime Contractor

Architecture Design

Miniaturisation

Mock-Up Testing

AAC Microtec

Uppsala

Sweden

Funded by ESA, Allocated in the Automation and Robotics Section:

Rate Sensor

Architecture Design

Breadboard Design &

Manufacture

Systems Engineering &

Assessment Ltd (SEA)

Bristol

England

Requirements

Sensor Data Processing

Breadboard Testing

German Research Centre

for Artificial Intelligence

Robotics Innovation Centre

Bremen

Germany

4

Introduction


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IMU• Rate and Acceleration sensors

• Dead reckoning of Orientation

• Gravity vector measurement

• Abnormal mode detection

Miniaturisation• Use MEMS Sensors

• Efficiently pack components to minimise

space, weight and power consumption.

• Sustain harsh space environment.

• See also Session 2A: “Miniaturised

Motion Controller for Space Robotics”

Rover for Extraterrestrial Planetary Exploration• Harsh Environment

• Tight Constraints in Space, Mass and Energy

• High Requirements on the navigation system.

5Multi Wafer Hybrid Integration: Rover IMU 1

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Requirements

6

Requirements

• Baseline Requirements

• Using SEA„s MRMS space-qualified Gyro

• Limited Start-Up Time

• Slipping / Sliding Detection

• Operate at -55°C to 70°C

• Radiation (from [1]):

2.5 mm aluminium shielding,

Total dose of 10 krad

Operation: SEE < 37 MeV cm2/mg

Resume operation: SEE < 75 MeV cm2/mg


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Requirements from Statement of Work

Support localisation on planetary terrain with an accuracy of

better than 2% over a representative trajectory.

CAN Interface (acc. ECSS-E-50-09, sec. 5)

Power Interface (acc. ECSS-E-20A, sec. 5.6 and 5.7)

Mars & Lunar Surface Operation

Tolerant to Radiation occurring at transfer and operation

Survive unpowered in -135°C to 70°C with 0 to 7 mbar and

on earth (1bar).

Mass < 200 g and power consumption < 1 W.

Provide real-time data when powered. 3-axis rates and

accelerations, sensor temperatures and housekeeping data.

[1] NASA 431 RQMT-000045 Rev. B

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Rover Navigation

Lunar Mission (from Next-LL)

• Analysis of soil samples every 100m.

• Service of seismometer payload

• Serivce of Lunar Radio Astronomy Explorer Navigation by

• Dead reckoning:• Error depends on

• traveled distance

• Short term

• SLAM:

• Limit the growing error

of dead reckon

• Long term


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IMU => Limit the computational load while having a good accuracy in the

100m range

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Sensor Error

• Simulated Worst Case Error

• Assumed IMU + Odometer

Angular Random Walk

Rate Bias Stability

Garvity Vector Error

• Rate Sensors is available

• Accelerometer is not at the

moment

• Requirements are relaxed

for faster rovers.


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• 100 m (5% Error)

• 10 m


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Architecture

10

IMU Design

ACC GYRO

S/H S/H

ADC DAC

S/H S/H

ADC DAC

FPGA/ASIC

Heater

proc/FPGA

FLASH RAMxtal DC/DC converter

+68V,+5V,-5V,+3.3V,+1.5V

ctrl

Connector

28VDCCAN

SENSOR UNIT

CORE UNIT (opt.)

POWER SUPPLY UNIT

S/H

DAC

EEPROM

Connector

SENSOR CONTROL UNIT


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11

Alternatives

Alt. 1 Alt. 2 Alt. 3 Alt. 4

Estimated volume and

weight including

casing

1000cm3 / 450g 545cm3 / 245g 291cm3 / 185g 180cm3 / 143g

Power consumption

[AD5]

4,8W incl filter/

4,0W no filter

4,8W incl filter/

4,0W no filter

3,4W incl filter/

2,6W no filter

2,6W incl filter/

2,0W no filter

Required packaging

technology

development

None - Sensor front end

MCM (S/H)

- Sensor common

MCM

- FPGA and/or µ-

processor

interposer

- Mixed signal

ASIC on

interposer

- Sensor common

MCM

- FPGA and/or µ-

processor

interposer

- MCM with

FPGA/µ-controller,

RAM and flash

memory

- MCM including

mixed signal ASIC

and sensor

detectors as bare

die.

Critical components None - S/H as bare dies - Mixed-signal

ASIC

- Mixed-signal

ASIC

- Sensors as bare

dies.

Required new

component

development

None - If RTAX FPGA:

new interposer

design needed

- If RTAX FPGA:

new interposer

design needed

- If RTAX FPGA:

new interposer

design needed

Other needed

developmentPSU design PSU design PSU design PSU design

Critical items related

to packaging with

respect to the

environmental

requirements

None - BGA I/F (large

MCM)

- BGA I/F (high

density I/O MCM)

- Coating of MCM

- BGA I/F (high

density I/O MCM)

- Coating of MCM

- BGA I/F (large

MCM)

- BGA I/F (high

density I/O MCM)

- Coating of MCM

- Sensor mounting

as bare dies on

ceramic

substrates.


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12

Critical Items

• System Design

Accelerometer accuracy

PSU design

• Components

FPGA as bare die

Qualification of small passives

S/H availability as bare dies

• Miniaturization

BGA solder joint reliability

Sensor mounting and naked die preparation for flip-chip

Failure mechanism of internal routing cracking

Coating reliability

Break-Down voltage between BGA I/Os


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13

Miniaturisation

Test Samples


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14

Material Tests

• Tested: Si and LTCC interposers

• Vibration Test

• Shock Test 1500g

• Thermal cycling , survival

-135 to +85°C

• Life-time testing, Thermal cycling

operation -55 to +100°C

• Vacuum environment

• Inspection

• X-Ray

• Electrical

• Visual inspection of surface protection


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15

Material Test Results

• Vibration passed

• Shock passed

• Micro cracks due to too fast cooling after soldering and too high CTE (coefficient of thermal expansion)

• Thermal cycling (survival) partially compliant. Problem related to unsuitable underfill and soldering

• Thermal cycling (operational) partially compliant for SI interposers.

• Vacuum passed.

Micro cracks

LTCC

STABLCOR

Solder

sphere

LTCC

Carrier board

Cu/Ni/Au solder pad

Pb63Sn37

solder paste

Pb90Sn10 non-collapsing

solder sphere


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Hardware Concept

Breadboard

17

Breadboard Modules


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The IMU Breadboard Concept Design Integrates the

following Main modules:

► Existing Single axis SEA Gyro Module (consisting of a single AIS

Phase II Detector), Flight Experiment on Cryosat2

► Existing DFKI dual axis commercial Gyro module (consisting of

commercial gyro‟s and a commercial uP with an integrated software

Kalman Filter and a CAN interface).

► New triple axis commercial Accelerometer module (consisting of 3

single axis accelerometers, signal conditioning and an ADC)

„Towards a European MEMS Inertial Measurement Unit (IMU) Capability“ GNC 2011

18

Architecture


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IMU Breadboard Demonstrator Architectural Design


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Integration of DFKI Module/ Accelerometer PCB/ Gyro into IMU Breadboard

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IMU Breadboard


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Power Input

CAN Interface

CSI PCB

DFKI Module

(under)

FEE PCB

(under)

PSU PCB

(under)

Accelerometer

PCB

(under)

Mechanical

Base Plate

21

Gyro Calibration


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SEA Gyro Rate

Table & Controller

Rate Table Testing @

+/- 24 deg/sec

22

Gyro Error Plot


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Robotic IMU SEA Gyro Rate Error Plot

Dynamic Range

+/- 24 deg/sec

Scale Factor

0.015643

Scale Factor Error

<2000ppm


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System Breadboard

Testing

24

Breadboard Testing

• Robotic Arm (DFKI)

Check the calibration

Determine the sensors capabilities for generic trajectories

• Rover Tests (DFKI, ESTEC)

Test the hardware for their targeted purpouse

Test in on target Platform


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25

AllanVariance


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ARW BSRate random

walk

SEA gyro0.018 °/sqrt(h) 1°/h 5 °/h/sqrt(h)

Velocity

random walk

[m/s/sqrt(h)]

Bias

instability

[m/s^2]

Acceleration

random walk

[m/s^2/sqrt(h)]

X-axis 0.84036 0.003045 0.00948

Y-axis 0.58309 0.001562 0.00617

Z-axis 0.58431 0.001280 0.00360

See Session 2B: “ESTEC Testbed Capabilities“

26

Robotic Arm

• “Sphere” Test

Commercial Sensor

corrupts the data.

Filtering with

Accelerometers improves

results


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Idx Start Time [s]

End Time [s]

Time Span [s]

ARW [rad/sqrt(s)]

0 5.94 60.77 54.83 0.0106021 75.99 125.91 49.92 0.0106832 141.93 192.75 50.82 0.0120133 207.17 257.01 49.85 0.0137314 269.67 311.94 42.27 0.0113395 333.92 377.86 43.94 0.0106076 399.01 445.48 46.46 0.0121287 465.1 510.46 45.36 0.016154

Mean: 0.012157

Std. Dev.: 0.001932

Just integrating the rate sensors

27

Asguard


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• Outdoor Test at DFKI

Mobil Robot

Fast, Agil, Low Signal to Noise

By summing up the

SEA gyro:

ARW: 92.82 °/sqrt(h)

28

ESTEC Rover

• At ESTEC Testbed

LRM Rover

Ackerman-Turn 2cm/s

• Results:

Square root fit (ARW):

0.83°/sqrt(h)

Linear fit (BS): 3.1°/h


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Conclusion

&

Future Work

30

Conclusion

• Miniaturisation is feasible and can be improve with better CTE match.

• The breadboard works reliable and delivers the required data.

• The commercial gyros introduce additional errors.

• The bias stability of the SEA gyro is within required limits.

• The angular random walk of the SEA gyro is within the required limits as a single sensor but could not be shown on the system due to errors added by the commercials sensors.

• The acceleration sensors are very close to the required limits, and have better properties than expected.

Presentation title

05/07/2006

Properties Best found Expected (Required)

Angular Random Walk 0.832 /sqrt(h) 0.5 /sqrt(h)

Gyro Bias Stability 3.1 /h 5.0 /h

Accelerometer Stability 9.84 millig 75 millig (1.2 millig)

31

Further work

• SEA Harmonised Gyro and equivalent accelerometers for

all three axes

• Modifying the MRS Gyro circuit design to suit maximum use

of bare die

• A new PSU to minimise both power loss and physical size

• Modification of the current FPGA code to allow „flash-

based‟ FPGAs as bare die to be used and also enable in-

flight re-programmability

• Refining the test, analysis and processing methods to

achieve the best possible accuracy


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Systems Engineering & Assessment

Aerospace Division

Bristol, England

www.sea.co.uk

DFKI Bremen

Robotics Innovations Center

www.dfki.de/robotics

[email protected]

Thank you for your attention!ǺAC Microtec

Uppsala Science Park

www.aacmicrotec.com

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