AUTOMATIC VISUAL INSPECTIONOF ZIRCONITE BLOCKS

raw zirconite blocks finished zirconites

Zirconite blocks : the problem

Raw zirconite blocks are polished and converted into zirconites for use in jewelry.About 15% of blocks exhibit shape and dimensional defects, which interrupt thetransformation process if they reach the machines.

Human visual inspection is infeasible because millions of blocks per month areprocessed.

How to view, illuminate and inspect blocks ?

Zirconite blocks : approach

I. The first step is the requeriments analysis : what must exactly be done, why and under which operational restrictions ? Requirements Specification Document.

II. Once we have concluded that . . .• a machine vision approach is feasible lighting is critical!• machine vision is the best approach• the devised solution may be affordable for the customer and cost effective for the developer

then• design a system prototype Preliminary Design Document• evaluate its cost : hardware, software, risk, licenses, copies …• formulate an economic proposal • sometimes prepare a convincing demo = implement prototype

III. Propose either . . .• an in-depth study (more analysis) that is not for free Formal Report• to sign a contract and start the project Contract, Plannification Document, ...

Possible shape defects

Zirconite blocks : defect characterization

Possible dimensional defects• non-square base• | length or width nominal size | > tolerance, tolerance = 0.1 mm nominal sizes from 1.70 to 3.00 mm (height from 1.25 to 2.00 mm)

Backlight

Zirconite blocks : Lighting

FLD from Doal&Jenner (coaxial)

Zirconite blocks : Lighting

1 2 3 4

5 6 7 8

9 10

Correct blocks

The “museum of horrors”

Zirconite blocks : Lighting

1 2 3 4

5 6 7 8

9 10 11 12

Zirconite blocks : Lighting

13 13bis 14 15

16 17 18 19

20 21 22 23

Zirconite blocks : Lighting

24 25 26 27

28

Zirconite blocks : Lighting

Background : the different of shades of black

velvet tire rubber black mate spray paint

We must maximize the difference between backgound and black grey levels so as tocorrectly and reliabily segment and measure the blocks.

“Black” must be• really black, not just dark• very diffuse

Zirconite blocks : Lighting

2: progressive camera, with wide open aperture and shutter 1/1000

5: rectified coaxial lighting

6: fiberoptic photosensor

7: rotation motor and painted platform

8: manual speed control

3: extensor tube 20mm

4: lens f=50mm

1

2

4

1: closed dome with black painted inner walls

3

5

6

7

8

Zirconite blocks : Lighting

fiber optic to photosensor

fiber optic from infrared LED

beamsplitter

Zirconite blocks : Lighting

Zirconite blocks : Defect detection

X2 = A1 / (A1+ A2)

A1A2

L1

L2

D2 D1X1 = 1 D2 / D1

X1 = 1 D2 / D1

right X1 = 1 D2 / D1

Zirconite blocks : Defect detection

Zirconite blocks

What would we do if ...

• not only the upper face had to be examined but also lower or side faces in order to detect lack of material not visible from above ?

• the height of the block must also conform to a certain tolerance ? Height varies 2 mm. (depth from focus ?)

• 6 parts per second have to be safely inspected ? That means high base speed, less time to acquire each image or otherwise the camera will yield blurred images

• we are later told that blocks can be o several grey shades ?

And how much would the proposed solutions cost in terms of hardware and labour time ?

There is not such a thing as a simple machine vision problem : the risk of a project should never be underestimated