Understanding And Applying Machine Vision Part 13 ppsx

When a small area of the image has little variation of discrete tonal features, the dominant property of that area is gray shade.. When a small area has wide variation of discrete tonal

Pixel pattern Most tesselations are square (square pixels); some are rectangular (rectangular pixels)

Texture

Local variation in pixel values that repeats in a regular or random way across a portion of an image or object Texture

is concerned with the spatial distribution of the gray shades and discrete tonal features When a small area of the image has little variation of discrete tonal features, the dominant property of that area is gray shade When a small area has wide variation of discrete tonal features, the dominant property of that area is texture There are three things crucial in this distinction: (1) the size of the small areas, (2) the relative sizes of the discrete tonal features, and (3) the number of distinguishable discrete tonal features

brightness value, a single color value, etc.) Local threshold: When threshold result depends on comparison of a joint local property and a characteristic pixel value with a single decision value, e.g., Threshold is based on comparing the difference between pixel value and neighborhood value with a global value

Thresholding

Scene segmentation process based on converting a gray scale image into a binary image by reassigning pixel gray levels to only two values Regions of an image are separated based on pixel values above and below a chosen intensity level

Goal-directed image analysis approach in which the interpretation stage is guided in its analysis by trial or test

descriptions of a scene Sometimes referred to as "hypothesize and test."

Tracking

Processing sequences of images in real time to derive a description of the motion of one or more objects in a scene

Passage of light or other signal.

Transmittance, Transmittance Coefficient

Ratio of the energy per unit time per unit area (radiant power density) transmitted through the object to the energy per unit time per unit area incident on the object In general, transmittance

Method of determining distance by trigonometry

Two and One-Half Dimensions (2 1/2 D)

Photometric stereo; see Needle Diagram

U

Ultraviolet (UV)

Region of the electromagnetic spectrum adjacent to the visible portion of the spectrum but with wavelengths between

100 and 400 nanometers

Union (of Two Images)

Logical operation forming a new image that is black at all points where either of the two images are black

Image in electronic signal format capable of being displayed on a cathode-ray tube screen The video signal is

generated from such devices as a vidicon or flying spot scanner, which convert an image from photographic form to video signal form by scanning it line by line The video signal itself is a sequence of signals, the signal representing the line of the scanned image

Process of understanding the environment based on sensing the light level or reflectance property of objects

Von Neumann Architecture

Current standard computer architecture that uses sequential processing

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Appendix B—

Machine Vision Application Checklist

This is a form to assist in developing ideas and requirements for machine vision applications It contains many typical questions to help determine feasibility, benefits and cost Permission is granted to use this form

Section 1—

Production Process

1 What do you make?

2 How do you make it?

3 What is the expected life of the product?

4 Is the product and the problem going to be around long enough to justify the purchase of a system?

5 Why do you need to inspect or control the process? Are there problems? Is process improvement the goal?

6 What is the current reject rate of bad parts?

7 What is the accuracy of the current inspection system?

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8 If you inspect or improve control, what are the specific benefits you expect to achieve?

9 Will the system be for a new line or an old line (retrofit)?

10 Does your application involve: one object at a time?

Multiple objects? How many different objects?

What are the different part numbers?

11 Is it a batch operation? or a continuous dedicated process/line?

12 What are the changeover times and the frequency of changeovers?

13 What are the skill levels involved in changeover?

14 How is inspection and/or function to be replaced currently being performed? Is it effective?

15 Is inspection to be: On line? or Off line?

16 Must every produced item be inspected, or can you randomly sample?

17 Will new part models or variations be added to the system at a later date? Define any potential future inspections that may be required of the same machine vision systems:

18 Are product design or production process changes anticipated?

19 Where do parts come from?

20 Can rejected parts be repaired?

21 Can vision assist in the diagnosis?

22 Where do pass and fail parts go?

23 When is the machine vision system needed by?

24 How many shifts will the system be used?

25 How many lines/machine will the vision system be needed for?

26 What is the attitude of the plant floor people towards machine vision/automation?

27 What is the attitude of the plant's management toward machine vision/automation?

28 What is your attitude towards machine vision/automation?

29 Can a representative sample of parts be provided to system vendors or integrators for evaluation?

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30 Can drawings be provided?

31 Can video of line be provided?

32 Can the vision suppliers observe production at your facility?

Section 2—

Benefits of Inspection

1 When an incorrect or flawed part escapes detection, what are the downstream effects? (quality, repair, machine downtime, etc.):

2 If a bad part is assembled, does it cause problems with the overall assembly?

3 If inspection is implemented, can any downstream testing requirements be relaxed?

4 If inspection is implemented, do you expect the yield through test to be improved?

5 At the inspection point, what is the cost (qualitative or quantitative) of a bad (faulty) part that escapes?

6 At the inspection point, what is the cost (qualitative or quantitative) of a good part that is falsely rejected?

Section 3—

Application

1 Describe the application:

2 What distinguishes a bad part from a good part?

3 Generically, does the application involve:

Gaging? (Show a sketch or drawing, if possible Highlight critical items.)

What are tightest tolerances? On what specific dimension?

What is the design goal for accuracy?

What is the design goal for repeatability?

Are there features that serve as references?

Describe calibration requirements:

Page 384Assembly Verification?

Dimensions of assembly:

Presence/absence:

Orientation:

What is the smallest piece to be verified?

What are the dimensions of that piece?

What is the largest piece to be verified?

What are the dimensions of that piece?

Do you also need to verify the correctness of the part?

Flaw inspection?

Describe flaw types:

What is the smallest size flaw?

Does the flaw affect surface geometry?

Does the flaw affect surface reflectivity?

Is it more of a stain?

Is classification of flaws required?

Location analysis?

What is the design goal for accuracy?

What is the design goal for repeatability?

What is the area over which "find" is required?

Describe calibration requirements:

Pattern recognition?

What is the size of the pattern?

Describe the differences between patterns:

Is there a background pattern?

Color?

Geometric?

Number of different patterns?

Purpose: to identify? to sort? other?

Page 385Are pattern differences geometric?

Are pattern differences photometric?

Are pattern differences color?

Is application specifically OCR? OCV

Handwritten characters? Fixed font? Variable font?

What is the height of the characters?

What is the stroke width?

What is the spacing between characters?

What is the spacing around the characters?

How many characters in a string?

How many lines?

Describe background

What is the color of the characters?

What is the color of the background?

Section 4—

Part to Be Inspected

1 Describe the part(s) to be inspected (consider those conditions that can change appearance of part or background) Are drawings available?

2 What is specific material (steel, plastic, etc.)?

3 What is specific finish (texture) like?

Is the surface finish the same on all faces of the part?

Is the surface finish the same for all part numbers and/or production runs?

Describe any differences:

Describe the platings:

Coating?

Thin films (oils, mist, etc.)?

Paint? Dull? Glossy?

Page 386Specular? Highly reflective (mirror like)? Poorly reflective? Dull? Matte?

Will the reflectivity of the part change from part to part?

Over time?

4 Are there any machining marks on the part?

Does the part generally have scratches, nicks, burrs, dents, etc.?

Is there any porosity on the parts?

5 What are the object's shapes? —Flat? Curved? Gently curved? Other?

Irregular? Grooved surface?

Sharp radii (prismatic)? Mixed geometric properties?

6 Is part always oriented in the same direction?

7 What is the temperature of the part?

8 What is the size of part(s)?

Smallest:

Largest:

9 Are there different colors for different models?

Does the color of the part change from part to part?

Color:

- single hue

- variations in saturation

- subtle color variations

- discrete color variations

- mixed with broad and discrete colors

10 Discuss conditions such as warpage, shrinkage, bending that could be experienced

11 Is there any change in appearance over time due to environment? (rust inhibitors, corrosion, lubricants, dirt,

perishability, etc.)

12 Are there any markings on the part?

13 Is it possible to make a refernce mark on the part, if necessary?

14 What are part appearance variables?

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15 Is surface translucent?

Describe variations in translucent optical density/degree of opaqueness:

16 Is surface transparent? Totally? Partially?

17 Is part sensitive to heat?

18 Is object sensitive to light?

If yes, what type of light?

1 Describe the material handling system (current or planned):

2 Is object subject to damage in handling?

Describe precautions to take in handling:

3 Will inspection be done at a station that also performs other functions?

Describe those functions:

4 What is the production rate? (How many parts per minute on average?)

During production catch up mode or peak rates?

5 Are there any expected changes that might affect the above rates?

6 Are parts static/indexed? or moving continuously? If indexed:

How long stationary?

Total in-dwell-out time:

What is the settling time?

Is there any acceleration and, if so, where in the cycle?

If parts are moving continuously, what is the speed?

Regulation of that speed?

+/- degrees around X direction

+/- degrees around Y direction

+/- degrees around Z direction

8 How much spacing is there between parts? Is the spacing random? or constant?

Part spacing repeatability:

Do parts ever touch?

Do parts ever overlap?

9 Is there more than one stable state involved? How many?

10 If there will be multiple inspections, will the part maintain the same orientation throughout the process?

11 What is the volume envelope available for an inspection station?

12 Are there any restrictions or obstructions to viewing the product?

13 Is there a weight constraint?

14 How close can an associated electronic enclosure be located?

15 How far will the vision system controller be from other equipment that the system will be interfaced with?

16 Describe any other physical constraints surrounding the proposed installation site:

17 If conveyor - what type?

What color?

What are the appearance variables of the conveyor (specular, uniformity, over time, etc.)?

18 Is a by-pass mode required?

19 Describe action to take when reject is detected:

Page 389Describe additional action desired if several consecutive objects are rejected?

What should be the number of consecutive rejects that trigger that action?

Section 6—

Operator Interface

1 Describe the operator interface that you would like Try to keep it as simple as possible Describe ''must have" items and then "like to have"

must have items:

like to have items

2 Describe the operators who will operate the equipment - educational level, familiarity with machinery, electronics, computers, experience, etc.:

3 Describe personnel access requirements (password protection, etc.):

4.Are there specific enclosure requirements?

5 Is it desirable to have display of objects under test?

6 Is it desirable to be able to display the last reject condition?

7 Is fail-safe operation required (i.e., part considered a reject unless it passes)?

8 What are the desired program-storage requirements?

9 What are the desired data-storage requirements?

10 Power-failure program storage preservation? Yes No

Power-failure data storage preservation? Yes No

11 Describe reporting requirements:

Must reports be generated without interrupting inspections? Yes No

12 What type of data will the system be required to display to a CRT or communicated to an external device?

If statistics are required, how often will the reports be generated?

Will the reports need to be printed and/or displayed?

13 What false reject rate is acceptable?

14 What escape rate or false acceptance rate is acceptable?

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Section 7—

Machine Interfaces

1 Alarms desired?

2 What other machines must this system be integrated with mechanically or electrically?

3 What event will trigger an inspection?

How will the event be detected?

How will this be communicated to the inspection system?

4 How will the results of the inspection be communicated and implemented?

5 Describe machine interfaces required/handshaking signals, etc.:

part in position sensor type

opto-isolation AC DC

voltage level signal conditioning required

RS 232 RS 422 RS 449 IEEE 488 PCI

Parallel PLC MAP

Ethernet Other interface details:

6 Describe hierarchical interfaces anticipated (to host computer, PLC, etc.)(data, programs, etc.):

Lubricant on parts:

5 Wash-down requirements:

6 Corrosive atmosphere:

7 Temperature range: Operating Storage

8 Humidity range: Operating Storage

2 Number of hours available for maintenance per week?

3 Describe calibration procedures required:

4 Describe challenge procedure to routinely verify performance:

5 Maintenance time between failures allowed:

6 Maintenance time to repair allowed:

7 Response time to service:

Section 10—

Other Issues/Requirements

1 Special paint colors:

2 Shipping:

8 Training - Where and when?

Details (subjects to be covered):

operator:

maintenance:

programming:

For how many?

9 Software Issues - ownership of

Revisions

Will vendor be required to support?

For how long?

Who will make software changes?

Who will be responsible for cost?

Page 393Who keeps backup?

Is there a license fee?

10 Hardware Issues

-Who is responsible for changes?

Who is responsible for spares?

11 Describe any safety issues that must be considered:

Section 11—

Acceptance Test/Buyoff Procedure

1 How will we be sure the machine is functioning properly? (Describe performance test hurdles.)

2 Tests at vendor site:

a Can good, bad, and/or marginal parts be provided?

b What is the sample-size for each challenge?