ndt project

7/30/2019 NDT Project

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Non-Destructive Testing of

Fruit Firmness with Real-Timeconstraints

Christopher Mills

Supervisors: Dr. Andrew Paplinski

Mr Charles Greif


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Contents

Research aims

Fruit Firmness

Non-destructive testing (NDT)

Methods

Completed work

Future work

Conclusions

References


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Project Aims

With our background research in Ultrasonic imaging, theaim is to design a simple system that will grade fruitfirmness using NDT

And as part DigSys we are interested in an ASIC application

of these algorithms. They can execute up to one hundredtimes faster in hardware.

Ensure that the system could be used in an industrialsetting, i.e. testing fruit on a rapidly moving conveyer belt.

Work within hard real time constraints (ie 10 fruit/sec) Be able to test fruit without actual contact with the skin of fruit (is this

possible?)


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Fruit FirmnessDefinition of fruit firmness mechanical rigidity of fruit cell

structure. It can be measured by conventional means;stress testing, Magness-Taylor Probing

Measurement of Fruit Firmness is important because

Firmness affects the perception of enjoyment of food. Perception of firmness is linked to freshness and the ripeness of

fruit. Such perception may be of greater importance for the preparation

of fruit for later consumption. (Preservation: canning,preserve/jam, etc)

Humans decide fruit firmness in a variety of ways Feel/look as fruit is consumed. Response to preparation/cooking.


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Fruit Firmness (cont) Biological factors of Fruit Firmness

Cell size/shape

Cell water content

Cell organization

Firmnessvaries with Fruit type (apple, orange)

Fruit Age (under ripe, over ripe)

Conditions during maturation and storage

The image on the right, shows what apple cells look like at highmagnification, the boundaries between the cells are visible.

Image of boiled apple cells at 100x magnification


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Fruit Firmness (cont)

Ultrasonic reflection can be used to measurefirmness. it will be the gaps between cells that will best

respond to ultrasound and describe firmness.

The image to the right is a representation of a

fruits internal structure. Fruit firmness varies with ripeness and time,

going from firm and unripe to soft and ripeor overripe.

The reason for this is that chemical changeswithin the fruit change the way the cellsinside interact and the chemical compositionwithin the fruit, eg starch being convertedinto sugars.


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Fruit Firmness (cont)Fruit firmness testing is critical to

industries involved in thesorting and grading of fruit. Assorting can be done based onfruit firmness measures.

For the duration of thisproject, a company calledColour Vision Systems (CVS)will be providing sponsoringfor this project. CVS build large scale fruit

sorting machines, including

computational circuits forautomated sorting based onvision for blemish detectionand near infrared for sugarcontent evaluation.


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Non-Destructive Testing

NDT methods of testing are used on mechanical structureswhile they are in use or before use and the structures cancontinue to be used post testing.

Various modalities of NDT exist, such as Sound methods (ultrasound, acoustic, etc)

Wave energy response (laser, infrared, x-ray)

Vision (Video cameras)

Physical Response to small force (Laser air puff, bounce test, micro-deformation)

Many researchers have attempted to develop methods forfruit firmness testing. For the next few slides I will detailsome of these.


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NDT-Examples, Laser scatter imaging

Kang et al attempted to use laser-scatter imaging to gradequality of tomatoes.

The method is reasonably simple, a laser beam is fired

through a piece of fruit/vegetable, the scatter of the laserbeam is recorded by a camera, and the extent of thescatter is an indication of quality.


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NDT-Examples, Laser Air Puff

McGlone et al describes a method based on the laser air pufftest.

The laser air puff test uses deformation in the target caused

by air under pressure, this deformation is measured by alaser.

It was found that while this method was reasonably accurateon average, there was an issue with confidence and

resolution when testing firm fruit due to the decreasedmeasurable deformation.


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NDT-Examples, Bounce Test

Delwiche et al attempted to build a fruit sorter based on theimpact force (or Bounce) testing method.

Based on previous work by the same researchers, built asystem where fruit would fall with a speed of 76.7 cm/s.

The force measurement was made by a force transducermounted vertically on a large steel mass or impact mass.The fruit was dropped from a conveyor belt. Overall, thesystem could process fruit at 5 fruit/s.

While the system was capable of sorting fruit based on

firmness, the error rate was high, 26% for peaches.

For this research, we will concentrate on ultrasonic methods tomeasure fruit firmness due to our experience in the area.


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NDT-Examples,Acoustic

Peleg et al built a fruit firmness sorter based on the principles ofacoustic energy.

A small electrodynamic shaker, vibrates the bottom of the fruit

The root mean square (RMS) level of the input signalXiismeasured in the shaker head

The output RMS signal levelXo is measured by a miniatureaccelerometer attached to the top part of the fruit.

A Firmness index PFTis defined by: PFT=X0/(X0-Xi).

Overall, the system performed well with reasonably high confidence

and repeatability (>80%).


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The picture on the rightshows the sensor wheel.

Fruit moves along theconveyor

Then its grabbed by theacoustic transducers

The fruit is held and testeduntil it reaches the lowerconveyer

The fruit is tested at a rate of7.5 fruit/s per lane.


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The table to the rightshows some values ofPFTvs Penetrometer force

It shows that the measurePFT is related to the force

measured by thepenetrometer

If the fruit is stored in aControlled Atmosphere,the Penetrometer and PFT

show similar increase inreading


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NDT-Examples, Ultrasonic

Mizrach et al attempted to estimate fruitqualities from a Ultrasonic measure offruit firmness

The system used two transducers, one asreceiver, the other as a transmitter

The resulting signal was processed

The Frequency response Analysed

And the speed of sound through thetarget measured

The experiment focused on Mangos asthe test subject

Representationof the system


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The graphs on the right showthe received signal and theFourier transform that ofthat signal.

The results were compared toknown values of firm andsoft fruits and a firmnessmeasure made based onthe comparison.

The accuracy of this methodis reasonably high.


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The scatter plots hererepresent the accuracy of thesystem

The table below gives a value

called the Standard Error ofCalibration (SEC)


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NDT - UltrasoundBasics of Ultrasonic testing Required equipment

Transmitter and Receiver transducers Pulsar/Receiver unit External/internal microcomputer to store

results and control Pulsar/Receiver

Operation Pulsar/receiver applies voltage to the

transmitter Transmitter vibrates and creates high

frequency sound Ultrasound reflects whenever a change in

density occurs. Receiver responds to sound and sends a

voltage based on the amplitude ofreceived signal


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NDT - UltrasoundHowever, there is a problems with using Ultrasound. The most

common method of ultrasound is called contact using liquidimmersion. This is a problem because

In an automatic system, contact with the fruit could beawkward and expensive.

Application of conducting liquid could also be awkward.

One possible answer is to use Non-Contact Ultrasound (NCU).The system is very similar to liquid contact except

The Transducers do not contact the target Noise due to lack of contact

large reflections caused by sound waves entering targetconsidered as noise

To reduce reflection from transducer to air, an acoustic lensis used.


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NDTUltrasound (NCU)

The above image shows the behaviour of ultrasonic wavesusing NCU.


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Research Method Empirically determine response of the cellular structure of fruit to

ultrasound

Possibly use Field 2, which can produce images based onsimulation values or real readings from an ultrasonic system

However, we do not require images, just an overall

characterization of fruit firmness Devise a Neural Network structure or other type of system that is

capable of determining fruit firmness (e.g. statistical methods)based on the training data. Early testing of Neural Net to be donein Matlab

This is an example of Field 2

taking a source image andsimulating how it would look

through ultrasonic testing. The

same could be done with a

mock up of fruit internals.


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Proposed system

Use Ultrasound on fruit via non-contact transducers to measurefruit firmness.

Process Ultrasound response via a neural network that will requiretraining for each available fruit type, and evaluate fruit firmness.

Integrate with existing system manufactured by CVS

such as a vision system to detect blemishes (Some blemishes arecaused by fruit diseases that would effect firmness also)

Weight and volume information (fruit density could prove useful in

determining fruit firmness)


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Proposed system

The card to the right is called theOPCARD.

It is a PCI add on card

It is an Oscilloscope card designedfor ultrasound

It has an 8bit DAC

Highly Configurable

12.5MHz 100MHz SampF

High pass and low pass filters

The Transducer shown here is theAT50 from Airmar

Air contact transducer

Output signal Frequency of 50MHz
http://www.optel.pl/manual/english/opcard.htm


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Work Completed Research into Non-Contact Ultrasound (NCU)

Based on what I have learned, NCU is a very appropriate technologyfor this application. However, it is a relatively new method comparedto liquid immersion ultrasound, and apparently despite its advantagesnot widely used so sourcing NCU transducers has been difficult.

Classification system At this stage, a neural network is the most likely system to use for

classification of Fruit Firmness

Other systems are possible, such as pattern recognition methodsincluding statistical analysis.

Physical arrangement of system Some ideas have been discussed, such as the angle between the

emitter and receiver(s)

Angles of transducers to fruit surface


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Future Work

Testing of various methods including

Acoustic/ultrasound

Determine accuracy of NCU

Machine Vision

Laser Air-puff

Non-destructive deformation

Sensor Fusion

Construction of a system based on results of testing


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Conclusions

Ultrasonic testing can grade firmness with sufficient accuracy.

NCU is applicable in most situations where the more commonliquid contact Ultrasonic testing methods are used.

Sensor fusion is a sensible option in fruit firmness testing.


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References

Texture - http://www.ba.ars.usda.gov/hb66/021texture.pdf

Evolution Of Piezoelectric Transducers To Full Scale Non-Contact Ultrasonic Analysis Mode -http://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdf

Non-Contact Ultrasound: The Last Frontier In Non-DestructiveTesting And Evaluation -http://www.ultrangroup.com/pdfs/esm1.pdf

Field 2 -http://www.es.oersted.dtu.dk/staff/jaj/field/index.html
http://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdfhttp://www.ultrangroup.com/pdfs/esm1.pdfhttp://www.es.oersted.dtu.dk/staff/jaj/field/index.htmlhttp://www.es.oersted.dtu.dk/staff/jaj/field/index.htmlhttp://www.ultrangroup.com/pdfs/esm1.pdfhttp://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdfhttp://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdfhttp://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdfhttp://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdfhttp://www.ultrangroup.com/pdfs/WCNDT-NCU-64.pdf

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