me 4447 6405 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
ME 4447/6405 PowerPoint Presentation
Download Presentation
ME 4447/6405

Loading in 2 Seconds...

play fullscreen
1 / 58

ME 4447/6405 - PowerPoint PPT Presentation


  • 241 Views
  • Uploaded on

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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'ME 4447/6405' - mardi


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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:

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)

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
other components
Stationary “masking” disk

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

Quadrature
  • Two tracks (A & B) at 90 degrees offset.
  • Provide direction information.
  • Provides up to 4 times resolution.
encoder disks

Ryder Winck

Encoder Disks

Incremental Disk

Absolute Disks

Binary

Gray Code

absolute disk codes
Example: 3 bit binary code

Bit 0

Bit 1

Bit 2

Bit 0

Bit 1

Bit 2

Ryder Winck

Absolute Disk Codes
problem with binary code

Ryder Winck

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 code12

Ryder Winck

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.

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.

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_ _ _

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_ _ _

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

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 errors18
Encoder errors

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 errors19
Comment on pulse irregularity

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 errors20
More encoder errors

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

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?

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”

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 interferometer25
The Michelson Interferometer

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 interferometer26
Brief historical background

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 interferometer27
Why “lasers” ?

High coherence

Collimated

Predictable

Frequency known

Aaron Scott

What is a Laser Interferometer?
types of laser interferometers
Homodyne detection (standard interferometry)

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 interferometers29
Advantages of Heterodyne Detection

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 – already discussed (Michelson interferometer)

Heterodyne

Dual frequency,

polarized

laser source

Polarizing

beam splitter

Aaron Scott

How Do They Work?
resolutions and sampling rate
Representative values

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
applications32
Michelson used his interferometer to measure the rotation rate of the Earth

Perimeter of his ring was 1.9 km

Aaron Scott

Applications
applications33
3 axis ring laser gyro

Many winds of optic fibers achieve 1 km path

Sensitive enough to measure

Earth’s rotation despite small

size

Aaron Scott

Applications
applications34
Distance measurement

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
applications35
Other measurements made possible by re-arrangements of the light paths. We can measure

angle

straightness

flatness

parallelism

Aaron Scott

Applications
applications36
LIGO Laser 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
applications37
LISA Laser 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
references38
http://en.wikipedia.org/wiki/Interferometry

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
what is a lvdt
Linear Variable Displacement Transducer

- Electrical transformer used to measure linear displacement

Alexandre Lenoble

What is a LVDT ?
construction
Primary coil and 2 symmetric secondary coils

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 :

- Power supply :

- DC

- AC

Type of armature :

- Unguided

- Captive (guided)

- Spring-extended

Alexandre Lenoble

LVDT Types
dc lvdts
Easy to install

Signal conditioning easier (equipment part of LVDT)

Can operate from dry cell batteries

- High unit cost

Alexandre Lenoble

DC LVDTs
ac lvdts
Small size

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 :

- 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

Armature restrained and guided by a low-friction assembly

Alexandre Lenoble

Captive (guided) armature
captive guided armature49
Advantages compared to unguided armature :

- 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 armature51
Best suited for static or slow-moving applications

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

Alexandre Lenoble

Spring-extended armature
lvdt function

Alexandre Lenoble

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

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

Alexandre Lenoble

Summary
summary54
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
applications55
LVDTs find lots of applications in :

- automation machinery

- civil engineering

- power generation

- manufacturing

- metal stamping

- OEM (Original Equipment Manufacturer)

- aeronautics

- R&D

Alexandre Lenoble

Applications
applications56
Examples for OEM :

- 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
applications57
Examples for civil engineering :

- 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
references58
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