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ME 4447/6405. Microprocessor Control of Manufacturing Systems and Introduction to Mechatronics Sensors Optical Encoder: Ryder Winck Laser Interferometer: Aaron Scott LVDT: Alexandre Lenoble. Optical Encoders Introduction Optical Encoder Components Types of Optical Encoders

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Me 4447 6405

ME 4447/6405

Microprocessor Control of Manufacturing Systems

and

Introduction to Mechatronics

Sensors

Optical Encoder: Ryder Winck

Laser Interferometer: Aaron Scott

LVDT: Alexandre Lenoble


Presentation outline

Optical Encoders

Introduction

Optical Encoder Components

Types of Optical Encoders

Encoder Discs and Digital Codes

Encoder Reliability and Errors

Applications

Laser Interferometer

What is a Laser Interferometer

Types of Laser Interferometer

How Do they Work

Resolutions and Sampling Rate

Applications

Linear Variable Displacement Transducer (LVDT)

What is a LVDT

Types of LVDTs

How Do they Work

Resolutions and Sampling Rate

Applications

Ryder Winck

Presentation Outline


What is an encoder

Any transducer that changes a signal into a coded (digital signal)

Optical Encoders

Use light & photosensors to produce digital code (ie. Lab 3 encoder).

Most popular type of encoder.

Can be linear or rotary.

Ryder Winck

What is an Encoder?


Types of optical encoders

2 types of Optical Encoders: signal)

1. Incremental (Lab 3 encoder)

Measure displacement relative to a reference point.

2. Absolute

Measure absolute position.

Advantages – A missed reading does not affect the next reading. Only needs power on when taking a reading.

Disadvantages – More expensive/complex. Cost/complexity proportional to resolution/accuracy.

Ryder Winck

Types of Optical Encoders


Fundamental components

Light source(s) signal)

LEDs or IR LEDs provide light source.

Light is collimated using a lens to make the beams parallel.

Photosensor(s)

Either Photodiode or Phototransistor.

Opaque disk (Code Disk)

One or more “tracks” with slits to allow light to pass through.

Ryder Winck

Fundamental Components


Optical encoder components

Ryder Winck signal)

Optical Encoder Components


Other components

Stationary “masking” disk signal)

Identical track(s) to Code Disk

Eliminates error due to the diameter of the light beam being greater than the code disk window length.

Signal amplifiers and pulse shape circuitry.

Ryder Winck

Other Components


Quadrature

Ryder Winck signal)

Quadrature

  • Two tracks (A & B) at 90 degrees offset.

  • Provide direction information.

  • Provides up to 4 times resolution.


Encoder disks

Ryder Winck signal)

Encoder Disks

Incremental Disk

Absolute Disks

Binary

Gray Code


Absolute disk codes

Example: 3 bit binary code signal)

Bit 0

Bit 1

Bit 2

Bit 0

Bit 1

Bit 2

Ryder Winck

Absolute Disk Codes


Problem with binary code

Ryder Winck signal)

Problem with Binary Code

  • One angle shift results in multiple bit changes.

  • Example: 1 => 2

    • 001 (start at 1)

    • 000 (turn off bit 0)

    • 010 (turn on bit 1)


Problem with binary code1

Ryder Winck signal)

Problem with Binary Code

  • One degree shift results in multiple bit changes.

  • Example: 1 => 2

    • 001 (start at 1)

    • 000 (turn off bit 0)

    • 010 (turn on bit 1)

  • It looks like we went from 1 => 0 => 2


Gray code

One bit change per angle change. signal)

Bit 0

Bit 1

Bit 2

Bit 0

Bit 1

Bit 2

Ryder Winck

Gray Code


Converting from gray code to binary code

Copy MSB. signal)

If MSB is 1, write 1s until next 1 is met. If MSB is 0, write 0s until next 1 is met.

When 1 is met, logically switch what you are writing (1=>0 or 0=>1).

Continue writing the same logical until next 1 is met.

Loop back to step 3.

Ryder Winck

Converting from Gray Code to Binary Code


Example convert 0010 to binary code

Copy MSB: 0_ _ _ signal)

Write 0s until next 1 is met: 00_ _

Switch to writing 1s: 001_

Write 1s: 0011

Ryder Winck

Example: Convert 0010 to Binary Code


Example convert 1110 to binary code

Copy MSB: 1_ _ _ signal)

Write 1s until next 1 is met: 1_ _ _

Switch to writing 0s until next 1 is met: 10_ _

Switch to writing 1s until next 1 is met: 1011

Ryder Winck

Example: Convert 1110 to Binary Code


Encoder reliability and errors

Resolution signal)

Incremental where N=# of windows.

Resolution can be increased by reading both rising and falling edges ( ) and by using quadrature ( ).

Absolute where n=# of tracks.

Ryder Winck

Encoder Reliability and Errors


Encoder reliability and errors1

Encoder errors signal)

Quantization Error – Dependent on digital word size.

Assembly Error – Dependent on eccentricity of rotation (is track center of rotation=center of rotation of disk)

Manufacturing tolerances – Code printing accuracy, sensor position, and irregularities in signal generation.

Ryder Winck

Encoder Reliability and Errors


Encoder reliability and errors2

Comment on pulse irregularity signal)

It is a result of noise in signal generation, variations in light intensity, and imperfect edges.

It can be mitigated using a Schmidt Trigger, but this can lead to hysteresis.

Using 2 adjacent sensor will negate this problem.

Ryder Winck

Encoder Reliability and Errors


Encoder reliability and errors3

More encoder errors signal)

Structural Limitations – Disk Deformation, physical loads on shaft.

Coupling Error – Gear backlash, belt slippage, etc…

Ambient Effects – Vibration, temperature, light noise, humidity, etc…

Ryder Winck

Encoder Reliability and Errors


Applications

Any linear/rotary position/velocity sensing signal)

DC Motor control – robotics/automation

Mechanical computer mouse

Digital readouts for measurement gauges

Tachometers – planes, trains and automobiles

Ryder Winck

Applications


References

http://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpghttp://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

http://www.designworldonline.com/Uploads/Leadership/Encoder_Montage1.jpg

http://www.gpi-encoders.com/06_Technical_Articles.htm

http://books.google.com/books?id=CjB2ygeR95cC&pg=PA630&lpg=PA630&dq=optical+encoder+mechatronics&source=bl&ots=uPB9nyu0AP&sig=PJYTMIG1dJ6UOPzj6uNhvYx1xSE&hl=en&sa=X&oi=book_result&resnum=4&ct=result#PPA639,M1

http://books.google.com/books?id=gUbQ9_weg88C&pg=PA97&lpg=PA97&dq=optical+encoders&source=web&ots=X2AbRCs5bL&sig=d-otsCBPIq7KGQodesPx3QJ_qos&hl=en&sa=X&oi=book_result&resnum=3&ct=result#PPA98,M1

http://books.google.com/books?id=uG7aqgal65YC&pg=RA1-PA163&lpg=RA1-PA163&dq=optical+encoders&source=web&ots=6-NhfhYb-F&sig=uf-VtBwSPRNUaCfujxu0gFb-xqY&hl=en&sa=X&oi=book_result&resnum=5&ct=result#PRA1-PA163,M1

http://mechatronics.mech.northwestern.edu/design_ref/sensors/encoders.html

http://books.google.com/books?id=9e4Omibz3L4C&pg=PA395&lpg=PA395&dq=optical+encoders&source=web&ots=5bTXzKDiWG&sig=cGa9IdHuxw3Zq49SyVCJbzjGQnc&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPA410,M1

Ryder Winck

References


Laser interferometers

What is a Laser Interferometer?http://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

Types of Laser Interferometers

How Do they Work?

Resolutions and Sampling Rate

Applications

Aaron Scott

Laser Interferometers


What is a laser interferometer

Interferometry = “interference” + “measurement”http://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

Basic application: hi-res measurement of distances

Basic principle: superposition of light waves

Constructive interference

Destructive interference

Aaron Scott

What is a Laser Interferometer?


What is a laser interferometer1

The Michelson Interferometerhttp://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

Aaron Scott

What is a Laser Interferometer?

  • Difference in path length results in phase difference

  • Phase difference causes interference

  • Interference determined by analysis of fringe patterns


What is a laser interferometer2

Brief historical backgroundhttp://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

First American Nobel Prize in Sciences 1907

Optical precision instruments

Invented the interferometer

Most accurate measurement of c in his time

Disproved existence of ether with famous Michelson-Morley experiment

Aaron Scott

What is a Laser Interferometer?

Albert Michelson


What is a laser interferometer3

Why “lasers” ?http://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

High coherence

Collimated

Predictable

Frequency known

Aaron Scott

What is a Laser Interferometer?


Types of laser interferometers

Homodyne detection (standard interferometry)http://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

DC output signal from photodiode related to intensity of light from interference

Both beams have same frequency

Heterodyne detection

One beam is frequency modulated prior to detection

AC output signal of interference at the beat frequency (see board)

Phase determined by signal analysis

Aaron Scott

Types of Laser Interferometers


Types of laser interferometers1

Advantages of Heterodyne Detectionhttp://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

AC signal frequency can be greatly reduced

AC frequency = fbeat = fmod – fsignal

Detection at low frequency reduces effect of high frequency noise

Insensitive to ambient light and signal intensity

Aaron Scott

Types of Laser Interferometers


How do they work

Homodyne http://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg– already discussed (Michelson interferometer)

Heterodyne

Dual frequency,

polarized

laser source

Polarizing

beam splitter

Aaron Scott

How Do They Work?


Resolutions and sampling rate

Representative valueshttp://hades.mech.northwestern.edu/wiki/index.php/Image:Maxon-small2.jpg

Resolution

10 nm digital resolution

sub-angstrom analog resolution achieved by “external interpolation”

Angstrom, Å = 1  10-10 m

Sampling Rate

20 MHz

Aaron Scott

Resolutions and Sampling Rate


Applications1

Michelson used his interferometer to measure the rotation rate of the Earth

Perimeter of his ring was 1.9 km

Aaron Scott

Applications


Applications2

3 axis ring laser gyro rate of the Earth

Many winds of optic fibers achieve 1 km path

Sensitive enough to measure

Earth’s rotation despite small

size

Aaron Scott

Applications


Applications3

Distance measurement rate of the Earth

Profilometer to measure nanoscale surface features

Nanopatterning Lithography

Precision machining calibration

High-precision linear feedback encoder

Velocity measurement

Doppler shift along measurement path changes beat frequency

Aaron Scott

Applications


Applications4

Other measurements made possible by re-arrangements of the light paths. We can measure

angle

straightness

flatness

parallelism

Aaron Scott

Applications


Applications5

LIGO light paths. We can measureLaser Interferometer Gravitational-Wave Observatory

Gravity waves, predicted by Gen. Relativity, could be detected by sensing changes in length in perpendicular directions

Light bounces 75 times before returning to be combined

Each arm 4 km

Aaron Scott

Applications


Applications6

LISA light paths. We can measureLaser Interferometer Space Antenna

NASA/ESA expected 2018-2020

Similar to LIGO but MUCH larger

5 gigameter arm length

3 interferometers in 1

Aaron Scott

Applications


References1

http://en.wikipedia.org/wiki/Interferometry light paths. We can measure

http://en.wikipedia.org/wiki/Albert_Abraham_Michelson

http://encarta.msn.com/encyclopedia_761555191/Albert_Michelson.html

http://www.renishaw.com/UserFiles/acrobat/UKEnglish/GEN-NEW-0117.pdf

http://www.ligo-la.caltech.edu/contents/overviewsci.htm

http://lisa.nasa.gov/

http://www.maxvalue.co.th/download/Excel.PDF

DVD: “Albert A. Michelson Laboratory, History and Heritage” Public Release, NAWCWD, China Lake

Aaron Scott

References


Alexandre lenoble

LVDT light paths. We can measure

Alexandre Lenoble


What is a lvdt

Linear Variable Displacement Transducer light paths. We can measure

- Electrical transformer used to measure linear displacement

Alexandre Lenoble

What is a LVDT ?


Construction

Primary coil and 2 symmetric secondary coils light paths. We can measure

Coils are encapsulated in metal/Epoxy

- Ferromagnetic core

Alexandre Lenoble

Construction

Secondary #1

Primary

Secondary #2

Lead wires

Displacement

Moveable core


Lvdt types

- Distinction by : light paths. We can measure

- Power supply :

- DC

- AC

Type of armature :

- Unguided

- Captive (guided)

- Spring-extended

Alexandre Lenoble

LVDT Types


Dc lvdts

Easy to install light paths. We can measure

Signal conditioning easier (equipment part of LVDT)

Can operate from dry cell batteries

- High unit cost

Alexandre Lenoble

DC LVDTs


Ac lvdts

Small size light paths. We can measure

Very accurate – Excellent resolution (0.1 µm)

Can operate with a wide temperature range

(-65° F to +221° F) (30°F to 120°F for DC)

- Lower unit cost than DC LVDTs

Alexandre Lenoble

AC LVDTs


Cost per unit

- Unguided armature : light paths. We can measure

- DC : $485

- AC : $330

- Spring-extended armature

- DC : $1359

- AC : $1156

Alexandre Lenoble

Cost per unit


Unguided armature

Simplest mechanical configuration, armature fits loosely on the bore of the LVDT, being attached to the moving point by a male thread.

- Armature completely separable from the transducer body.

Alexandre Lenoble

Unguided armature


Unguided armature applications

Well-suited for short-range (1 to 50mm), high speed applications (high-frequency vibration)

Alexandre Lenoble

Unguided armature : applications


Captive guided armature

- Both static and dynamic applications applications (high-frequency vibration)

Armature restrained and guided by a low-friction assembly

Alexandre Lenoble

Captive (guided) armature


Captive guided armature1

Advantages compared to unguided armature : applications (high-frequency vibration)

- Better for longer working range (up to 500mm)

- Preferred when misalignment may occur

Alexandre Lenoble

Captive (guided) armature


Spring extended armature

- Armature restrained and guided by a low-friction assembly (as for captive armature)

- Internal spring to continuously push the armature to its fullest possible extension

Alexandre Lenoble

Spring-extended armature


Spring extended armature1

Best suited for static or slow-moving applications (as for captive armature)

- Lower range than captive armature (10 to 70mm)

Alexandre Lenoble

Spring-extended armature


Lvdt function

Alexandre Lenoble (as for captive armature)

LVDT Function

Primary coil

Primary coil

Secondary coil #1

Secondary coil #2

Secondary coil #1

Secondary coil #2

Input to primary

Input to primary

Output from secondary coils

Output from secondary coils

Secondary coil #1 output (V1)

Secondary coil #2 output (V2)

V1 - V2

Secondary coil #1 output (V1)

Secondary coil #2 output (V2)

V1 - V2

Demodulated output

Demodulated output


Summary

LVDTs are robust equipment for measuring displacement (as for captive armature)

AC LVDTs require separate signal conditioning equipment, while DC LVDTs include signal conditioning equipment on the device.

Alexandre Lenoble

Summary


Summary1

There are three types of LVDT: unguided armature, captive armature, and spring-extended armature.

AC LVDT’s cost less than DC, but the entire measurement system must be considered.

Alexandre Lenoble

Summary


Applications7

LVDTs find lots of applications in : armature, and spring-extended armature.

- automation machinery

- civil engineering

- power generation

- manufacturing

- metal stamping

- OEM (Original Equipment Manufacturer)

- aeronautics

- R&D

Alexandre Lenoble

Applications


Applications8

Examples for OEM : armature, and spring-extended armature.

- Measure displacement of thermostat valve stem for diesel truck engine monitoring system.

- Blood-testing device measuring the displacement of blood cells as they contract. Clinical usage, diagnosis of blood disorders.

- Measuring displacement of diamond tip to determine material hardness.

Alexandre Lenoble

Applications


Applications9

Examples for civil engineering : armature, and spring-extended armature.

- Displacement measurement of imbedded concrete anchors tested for tensile, compression, bending strength and crack growth in concrete

- Deformation and creep of concrete wall used for retaining wall in large gas pipe installation.

- Dynamic measurement of fatigue in large structural components used in suspension bridges.

Alexandre Lenoble

Applications


References2

www.dankuchma.com/cee498/presentations/LVDT%20Jason%20Hart.pptwww.dankuchma.com/cee498/presentations/LVDT%20Jason%20Hart.ppt

Pr. Kurfess’s lecture

http://www.daytronic.com/products/trans/lvdt/default.htm

http://www.macrosensors.com

Alexandre Lenoble

References


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