MARK LOONEY

MEMS Application Engineer

High-Performance MEMS

IMU Solutions for

Demanding Applications

02/17/2016

2

Inertial Measurement Unit (IMU) Basics

…sensor functions, coordinate basics

DOF = Degrees of freedom

An Inertial Measurement Unit provides a combination of linear, rotational, magnetic and barometric sensors

3-axis accelerometer (linear)

3-axis gyroscope (rotation rate)

3-axis magnetometer (magnetic field)

Barometer (altitude)

6DOF 9DOF 10DOF

Inertial Measurement Unit (IMU) Basics

…one primary purpose is to estimate orientation angles

PIN 1PIN 14

Accelerometers respond to their orientation, with respect to the earth’s gravitational

field. They are typically most influential for LEVEL FLIGHT state

Gyroscopes measure the angular rate of rotation, around their measurement axis; angle estimates come from integration. Typically most influential DURING MANUEVERS.

∅𝑑 𝑡 = 𝑡1

𝑡2

𝜔𝑚 𝑡 ∙ 𝑑𝑡

x

yx a

aa tan

Sensor Fusion

Real-time

angle estimation

g

aa x

x 1sin

4

Application Example

Industrial Inspection System

Image Stabilization enables productivity and

quality assurance

Industrial Inspection System

…swinging motion causes image distortion

5

Conveyor belt

Video

Camera

Swinging

motion

ωSW(t)

D

dSW

±φSW

Ideal center of

camera view

Industrial Inspection System

…understand basic geometry of the problem

6

Conveyor belt

Video

Camera

Swinging

motion

ωSW(t)

D

dSW

±φSW

Ideal center of

camera view

Dd

a

Dd

SWSW

SWSW

sin

sin

Industrial Inspection System

…MEMS Gyroscopes enable solution via Image Stabilization

7

Servo

Motor

Digital

Filtering

ADXRS290

MEMS

Gyro

Integrator

-

ωG(t)

φE(t)

φCOR(t)

Mechanical Connection

Calibration

Alignment

φCMD(t)

ωF(t)

φP(t)

Industrial Inspection System

…Image Stabilization, with MEMS Gyroscope Feedback

8

Conveyor belt

Video

Camera

Swinging

motion

ωSW(t)

D

dSW

±φRE

dRE

±φSW

Ideal center of

camera view

Industrial Inspection System

…evaluate residual error in geometric terms

9

Conveyor belt

Video

Camera

Swinging

motion

ωSW(t)

D

±φRE

dREIdeal center of

camera view

Key point

The residual error will be influenced by

the noise in the feedback signal…gyro

Dd

a

Dd

RERE

RERE

sin

sin

Industrial Inspection System

…so we can relate them to key gyroscope (ARW) metrics

10

-0.0015

-0.001

-0.0005

0

0.0005

0.001

0.0015

0 0.02 0.04 0.06 0.08 0.1

Inte

gra

tion E

rror

(degre

es)

Integration Time (seconds)

±φRE

ADIS16460 ARW =

0.17 /√hour

11

MEMS IMUS

Driving beyond the benign

…providing the best pointing/tracking

accuracy, in the toughest conditions.

So, can I use a consumer IMU for my industrial app?

…maybe

12

Applications: Simple Motion, Short Life, Error Tolerant

Other Non-Inertial Sensors more Highly Weighted

Operational Conditions Restricted/Constrained

Individual Specs: ‘OK’

Composite Spec (Attitude/Heading): 3-5o… (highly compromised)

Applications: Complex Motion, Long Life, Mission Critical

Inertial Sensors more heavily relied on

Complex/Unpredictable Conditions

Individual Specs: Strong

Composite Spec (Attitude/Heading): 0.3-0.5o (and better)

Consumer

MEMs

Industrial

MEMs

Technology CHASM

Today’s Best Consumer Devices result in 10X or lower Positioning

Accuracy Regardless of how much Sensor-Processing is done

► Core sensor expertise

► Interface circuit and packaging…preserving and capturing available

performance.

► Calibration: optimizing/improving performance

► Packaging, characterization of key behaviors, long-term

13

IMU Building Blocks

…more than just soldering a small, cheap IC on a PCB

► Best in class Gyro Performance

under rugged environmental

conditions

► Proprietary differential Quad-

Resonator structure offers superb

shock and vibration rejection

0.015 o/s/g

0.0001o/s/g2

► New in-plane Roll/Pitch Gyro With

Industry leading Noise

Performance

0.004 °/sec/√Hz

14

IMU Building Blocks

…Core sensor technology that is targeted for performance

15

IMU Building Blocks

…Typical performance gaps with core sensors

Rough road causes angular vibration

(±10°/sec) in the y-axis (pitch).

High cross-axis sensitivity (GCAS) will cause

angular jitter on the x-axis (roll).

ØROLL = 𝐆𝐂𝐀𝐒 x θPITCH

Typical Device Spec: +/-2% ADI Spec: <0.087%

Rough road causes up/down vibration

(±2g-rms) in the z-axis

High Linear-g sensitivity (GL) will cause

angular jitter on all three gyroscopes.

ØROLL = 𝐆𝐋 x 𝐴𝑍

ie: Vehicle-mounted antenna, camera,

laser, weapon, etc.

Typical Device Spec: 0.1 o/s/g ADI Spec: 0.015 o/s/g

Cross-Axis

Vibration

16

IMU Building Blocks

…Vibration/Cross-axis impact on spectral noise density

ADI Sensors Excel at Rejection of Vibration, and other

critical drift factors

ADXRS290

(Response to 15g random vib)

Consumer-targeted devices

(Response to 5g random vib)

Vib applied

along Z direction

► ADI Subjected to 3X Higher Vibration, shows 10X Better Response

18

IMU Building Blocks

…Vibration/Cross-axis impact on Stability

1000

1

10

100

0.01 0.1 1 10 100 1000 10000

RO

OT

AL

LA

N V

AR

IAN

CE

(°/

Ho

ur)

INTEGRATION PERIOD (Seconds)

10

27

7-0

07

+1σ

–1σ

AVERAGE

Some devices

with <2 °/hr of

In-run bias stability

Linear-g from ±10º of tilt

degrade to ~62º/hr ADXRS646, ~6.2º/hr

ADIS16488, ~ 5.6º/hr

Example

±10º Tilt with Linear-g

Only

• Linear-g can be

observed, compensated

and in some cases,

removed with filtering.

• The issue with rectified

(gxg) is that it is difficult

to observe and is one-

sided, so filtering results

in a bias shift.

• gxg is rarely specified

• One gyro’s performance

for gxg is 0.005°/sec/g2

• On this product, the

impact of a 2g rms

vibration would be

72°/hour!

Designing for Total Spec Performance

Why it Matters…

► Performance in a dynamic environment relies on more than in-run bias

stability

► Other specifications, such as vibration rejection, can be significant ‘spoilers’

► Key is well balanced Bias plus Linear-g rejection

in-run bias

(dph)

linear-g

(dps/g)0.1 0.05 0.015 0.01 0.001 0.1 0.05 0.015 0.01 0.001 0.1 0.05 0.015 0.01 0.001

linear-g effect

under 5deg tilt

(dph)

31.4 15.7 4.7 3.1 0.3 31.4 15.7 4.7 3.1 0.3 31.4 15.7 4.7 3.1 0.3

Total/Actual

Bias (dph) 33 18.6 11 10.5 10 32 16.5 6.9 5.9 5 31.4 15.7 4.8 3.25 1.04

10 5 1

Linear-g effect, under 5o tilt = (linear-g) x (sin 5o) x 3600sec/hour

Total Bias = RSS of in-run bias and linear-g effect

(ie: even a 10dph gyro, with 15mdps/g Vibration Rejection, can

perform better than a 1 dph gyro with 50mdps/g Vibration)

20

IMU Building Blocks

…calibration

Core

Sensor

Enhanced

Sensors

Application

Position/Motion

Information

Motion Dynamics

Expertise

Deep Application

Knowledge

inputz

inputy

inputx

zzzyzx

yzyyyx

xzxyxx

z

y

x

outputz

outputy

outputx

zzyzx

yzyyx

xzxyx

inputz

inputy

inputx

f

f

f

gGSgGSgGS

gGSgGSgGS

gGSgGSgGS

volttempgB

volttempgB

volttempgB

volttempgSFgMAgMA

gMAvolttempgSFgMA

gMAgMAvolttempgSF

,

,

,

,

,

,

,

,

,

*

,

,

,

*

,

,

,

2

,

2

,

2

,

,

.

,

,

,

,

*

0

0

0

)(

)(

)(

*

)(

)(

)(

inputz

inputy

inputx

zyzx

yzyx

xzxy

z

y

x

outputz

outputy

outputx

zzyzx

yzyyx

xzxyx

inputx

inputy

inputx

rr

rr

rr

tempaB

tempaB

tempaB

f

f

f

tempaSFaMAaMA

aMAtempaSFaMA

aMAaMAtempaSF

f

f

f

Gyroscopes

Accelerometers

21

ADIS16460

The latest….

…smallest, lowest noise…so much more

ADI Inertial Solutions for Navigation and Stabilization

3-Axis

MEMS

Gyro+ x Filtering

Correction

Formulas

(Temp, Vdd)Alignment

3-Axis

MEMS

Accel+ x Filtering

Correction

Formulas

(Temp, Vdd)

gx, gy, gz

ax, ay, az

ΔΘx, ΔΘy, ΔΘz

ΔVx, ΔVy, ΔVz

Magnetometers

(3x)Barometer

ADIS16334, ADIS16445

ADIS16488ADIS16448

ADIS16485

Compact 10 DoF

Tactical Grade 6 DoF

ADIS16448

Compact 6 DoF

ADIS16445/46X

Tactical Grade 10 DoF

ADIS16488A

Component Gyros

ADXRS646/29X

Dynamic Orientation Sensing• Extended Kalman Filter

ADIS16480

Component Accels

ADXL35X/203

23

Industrial IMU

…ADIS16460 is the latest in a long-term progression

ADIS1635X

ADI First to Market with Industrial Targeted IMUs

2007

ADIS1636X

2X Performance Increase; Interface/Footprint Compatible

2009

ADIS1644X

50% Size Reduction; Interface Compatible; 10 DoF

2012

ADIS16460

50% Size Reduction ; Noise, Stability, and Cost Improvements;

Now

ADIS1648X

4X Performance Increase; Tactical Grade IMU Family

2011

ADIS16460 Six Degrees of Freedom Inertial Measurement Unit

24

► Industry’s most affordable benchmark (cost and size) for High Performance Inertial Sensing

► Robust sensing measurements reduce the need for complex isolation or system level compensation

► System ready implementation through proven iSensor ® integration, calibration, and reliability

► Improved resolution and stability in machine positioning, particularly under dynamic and challenging environments

► Calibration, across temperature, on every device ensures best possible performance, and lower overall system cost

► Integration, and precision alignment, of industrial grade linear and rotational sensing cores, into complete sensor-fused IMU, with optimized embedded sensor processing

Key Benefits

Features and Specifications

ADIS16460 Six Degrees of Freedom Inertial Measurement Unit

► 6 DoF

Tri-Axis Linear and Rotational Sensing

► Random Walk

Angular: 0.1 °/√hr

Velocity: 0.002 m/sec/√hr

► Vibration Rectification Error

Gyro: 0.0004 °/sec/g2

Accel: 0.08 mg/g2

► Sensitivity Tempco

Gyro: +/- 20 ppm/°C

Accel: +/- 15 ppm/°C

► Cross-Axis Sensitivity: 0.08%

► Bandwidth: 375Hz

► Size: 22x22x9mm

25

► 50% Size Reduction over prior generations

► Lowest Noise Industrial Grade IMU in the

portfolio

► Targeted at High Volume (cost-sensitive)

Industrial Applications, which demand high-

performance

► Smallest Industrial-Grade IMU

► Industry Leading Vibration Rejection

Portfolio Positioning

Competitive Positioning

ADIS16460 Six Degrees of Freedom Inertial Measurement Unit:

Applications Example

► Problem: Correction for outages or inaccuracies

in primary sensing/feedback loops for

Guidance/Controls/Servos.

► Solution: Low Noise, Vibration Immune, Inertial

Sensing cluster reduces jitter, and provides

primary guidance during outages or disruptions of

other sensors

Low noise : 0.004 °/sec/√Hz rms

Linear Vibration Rejection: 0.01 °/sec/g

Alignment: 0.05 Degrees

Bandwidth: 375 Hz

Sample Rate: 2048 SPS

► Applications:

UAVs/Drones

Robotics

Smart Agriculture/Construction Machinery

Factory/Industrial Automation

IoMT (...Moving things…)

26

Navigation

Computer

GPS /

Other

IMU

Servos

Controls

Guidance

27

Getting started

Avoiding typical pitfalls

ADIS16460 Six Degrees of Freedom Inertial Measurement Unit:

Design Resources

► Data Sheet: ADIS16460: Available Now

www.analog.com/ADIS16460

► Evaluation Tools ADIS16IMU/PCBZ – Breakout Board

EVAL-ADISZ – Evaluation System

IMU Evaluation Software

► Videos High Performance MEMs: What does that mean?

Shock and Vibration Rejection of MEMs Gyroscopes

► Technical Articles ANTICIPATING AND MANAGING CRITICAL NOISE

SOURCES IN MEMS GYROSCOPES

► Inertial MEMS Community in the EngineerZone: https://ez.analog.com/community/mems

150+ FAQs

1300+ Discussions

200+ Active users

► Product home page: www.analog.com/ADIS16460

28

ADIS16460

ADIS16IMU4/PCBZEVAL-ADISZ

► Start with Datasheet, Application Notes (AN-1295, AN-1305) and 3-D

models on the web

► ACTION: Search “ADIS16485” and all will come up near the top of this

list, through the home page or as a result.

► Reference designs for using the ADIS16460 will be available soon!

29

Design Support

Mechanical Design Tips – It can impact performance

MATING CONNECTOR

MOUNTINGSURFACE

RIGID PCB

NOTES1. MACHINE SCREWS WILL NOT BE VISIBLE CROSS SECTION VIEW FOR ILLUSTRATION PURPOSES ONLY.

TAPPEDHOLES

MACHINESCREW HEAD

ADIS16488A

12

12

4-0

09

WASHER

► Power, SPI, auxiliary I/O

► Most often see figures like this in the datasheet.

► Not shown: Reset lines – Manage noise opportunity

Several cases of open-ended cable connections causing issue, some of them

when the customer had no plan to use the function?!!!

30

Design Support

Key Electrical Connections

SYSTEMPROCESSORSPI MASTER

SCLK

CS

DIN

DOUT

SCLK

SS

MOSI

MISO

+3.3V

IRQ DIO2

VDD

I/O LINES ARE COMPATIBLE WITH3.3V LOGIC LEVELS

10

6

3

5

4

9

11 12 23

13 14 15

ADIS16485

10

66

6-0

11

► Start-up transients…common for any embedded system

Initial charge of internal decoupling capacitors (24uF on ADIS1648x family)

Supply start-up transients demands

► Stay within operating range

Majority of failure returns have some sort of EOS

31

Design Support

Power Supply – It can prevent start-up/progress

10

66

6-1

29

CH1 2.00V

CH4 100mA Ω 1M POINTS

1.00ms 1.00MS/s CH1 2.72V

T 9.800%

1

4

T

VDD

CURRENT

10

66

6-1

28

CH4 100mA Ω 1M POINTS

1.00ms 1.00MS/s CH1 2.72V

T 9.800%

4

T

CURRENT

► Common reason that customers will say, “part is not working.”

► Not designed for long cables but it is possible with drivers/attention to

detail on the transmission lines.

► Use a repeating pattern: read PROD_ID. Should be correct, every time!

We have read parts for days without errors

► Use a scope to look for valid timing, sequencing, signal integrity, coding

32

Design Support

Data Communications - Serial Peripheral Interface (SPI)

SYSTEMPROCESSORSPI MASTER

SCLK

CS

DIN

DOUT

SCLK

SS

MOSI

MISO

+3.3V

IRQ DIO2

VDD

I/O LINES ARE COMPATIBLE WITH3.3V LOGIC LEVELS

10

6

3

5

4

9

11 12 23

13 14 15

ADIS16485

10

66

6-0

11

SCLK

CS

DIN

DOUT

DOUT = 0100 0000 0110 0101 = 0x4065 = 16,485 (PROD_ID)

DIN = 0111 1110 0000 0000 = 0x7E00

10

66

6-0

16

► Numerous examples on the web

► Phil Burkert, FAE-USA/Illinois developed an example for the ADIS16448:

EngineerZone: search “ADIS16448 code.” Top result:

https://ez.analog.com/docs/DOC-2993

► Other examples, with great comments on GitHub

https://github.com/juchong/ADIS16448-Arduino-Demo

https://github.com/juchong/ADIS16460-Arduino-Teensy

33

Design Support

Starter code

► Power supply measurement, at the device

► Power supply current close to typical in Table 1 spec (all datasheets)

► Read PROD_ID register in a repeating pattern to study for correct coding, sequencing, phasing, timing and signal integrity

► Accelerometers respond to ±1g orientations?

► Gyroscope integration around a fixed angle. Use a fixed table edge, like in this example: https://ez.analog.com/docs/DOC-2181

► Noise/stability:

Read rates synchronous with sample rates?

Part is on stable platform (no opportunity for vibration?)

Raw data…let’s take a look…sometimes “no function” comes with “high noise” initial report. 0xFFFF and 0x0000 look like a large span but in twos complement, they are only 1LSB apart.

34

Design Support

Troubleshooting tips

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