NonDestructive Testing of Fruit Firmness with RealTime constraints

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Non-Destructive Testing of Fruit Firmness with
Real-Time constraints

• Christopher Mills
• Supervisors Dr. Andrew Paplinski
• Mr Charles Greif

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Contents

• Fruit Firmness
• Non-destructive testing (NDT)
• Research Plan aims, methods, work to date.
• Conclusions

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Fruit Firmness

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

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Fruit Firmness (cont)

• Biological factors of Fruit Firmness
• Cell size/shape
• Cell water content
• Cell organization
• Firmness varies with
• Fruit type (apple, orange)
• Fruit Age (under ripe, over ripe)
• Conditions during maturation and storage

Image of apple cells at 100x magnification
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Fruit Firmness (cont)

• Fruit firmness testing is critical to industries
  involved in the sorting and grading of fruit. As
  sorting can be done based on fruit firmness
  measures.
• For the duration of this project, a company
  called Colour Vision Systems (CVS) will be
  providing support for this project.
• CVS build large scale fruit sorting machines, so
  their interest in such a system is obvious.

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Non-Destructive Testing

• NDT includes any methods of testing that do not
  cause damage to the target eg
• Ultrasound used to find impurities in steel
• Various modalities of NDT exist, such as
• Sound methods (ultrasound, acoustic, etc)
• Wave energy response (laser, infrared, x-ray)
• Vision (Video cameras)
• We will concentrate on ultrasonic methods to
  measure fruit firmness (most other methods are
  destructive)

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Project Aims

• With our background research in Ultrasonic
  imaging, the aim is to produce a simple system
  that will grade fruit firmness using NDT
• Ensure that the system could be used in an
  industrial setting, 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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Method

• Empirically determine response of the cellular
  structure of fruit to ultrasound
• Simulate response using a software package called
  Field 2, which can produce images based on
  simulation 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 or other type of system
  that is capable of determining fruit firmness
  (e.g. statistical methods) based on the results
  of experimentation

Field 2 can create images or simple signal over
time graphs, here is an example of field 2 taking
a source image and simulating how it would look
through ultrasonic testing. The same could be
done with a mock up of fruit internals.
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Method (cont)

• Possible Final system
• Use Ultrasonic methods on fruit via non-contact
  transducers
• Attempt to use information from external systems
  (if possible)
• such as a vision system to detect blemishes (Some
  blemishes are caused by fruit diseases that would
  effect firmness also)
• Weight and volume information (fruit density
  could prove useful in determining fruit firmness)
• Process all available information via a neural
  network that will require training for each
  available fruit type.

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Work to Date

• Research into Non-Contact Ultrasound (NCU)
• The conclusion is that NCU could possibly resolve
  the problem of using contact ultrasound, but
  finding sources for NCU transducers is proving to
  be difficult
• Classification system
• At this stage, a neural network is the most
  likely system to use for classification of Fruit
  Firmness
• Other systems have been considered, such as
  pattern recognition methods including statistical
  analysis.

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Work to Date (cont)

• Work to date (cont)
• Hardware Prototype
• Due to the difficulty with sourcing NCU, I have
  yet to begin the prototype. A full NCU
  implementation may be postponed and some work
  could be done using a dry-contact system
• 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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Conclusions

• At this point, I can see no reason why the system
  I propose would not work. I expect that I will
  have at least a functioning prototype and
  algorithm development with off-the-shelf
  equipment.