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Technology of Machine Vision Cameras

Ma­chi­ne vi­sion ca­me­ras play a cri­ti­cal role in vi­sion ap­pli­ca­tions, espe­cial­ly in au­to­ma­ted qua­li­ty con­trol. In com­bi­na­tion with ma­chi­ne vi­sion con­trol­lers and 2D image pro­ces­sing soft­ware, the high-​resolution image data is ana­ly­zed, and er­rors as well as ir­re­gu­la­ri­ties in pro­duc­tion pro­ces­ses are iden­ti­fied.

Definition
Technology Comparison
Areas of Usage
Surface and Line Cameras
Global and Rolling Shutter
Monochrome vs. Color Camera

What Is a Ma­chi­ne Vi­sion Ca­me­ra?

A ma­chi­ne vi­sion ca­me­ra, also known as an in­du­strial ca­me­ra, is a key part of a 2D image pro­ces­sing sy­stem. Its main func­tion is to cap­tu­re ima­ges, which are then pro­ces­sed by a com­bi­na­tion of hard­ware and soft­ware. The in­for­ma­tion ob­tai­ned is pre­pa­red for va­rious ap­pli­ca­tions.

A ty­pi­cal exam­ple of an image pro­ces­sing ap­pli­ca­tion in a ma­nu­fac­tu­ring sy­stem is qua­li­ty con­trol, pre­sen­ce con­trol and com­ple­te­ness con­trol. This in­vol­ves ana­ly­zing a spe­ci­fic fea­tu­re of a part that is pro­du­ced on an as­sem­bly line. In this way, it can be chec­ked whe­ther the part meets the qua­li­ty cri­te­ria or, if ne­ces­sa­ry, must be sor­ted out.

The ca­me­ra is part of the image pro­ces­sing sy­stem. This con­sists of the fol­lo­wing com­po­nen­ts:

Main Com­po­nen­ts of 2D Image Pro­ces­sing Sy­stems

Illumination icon gray
Illumination
Lens
Lens Filter
Machine Vision Camera
Machine Vision Controller
Software

Se­lec­tion Guide for the Right Lens

Find the right lens for your in­du­strial ca­me­ra ea­si­ly and au­to­ma­ti­cal­ly using the Vi­sion Cal­cu­la­tor:

The Dif­fe­ren­ce Bet­ween Ma­chi­ne Vi­sion Ca­me­ras and Smart Ca­me­ras

Ma­chi­ne Vi­sion Ca­me­ras

  • Image eva­lua­tion takes place via the ma­chi­ne vi­sion con­trol­ler and the image pro­ces­sing soft­ware

  • Mul­ti­ple ca­me­ras can be con­nec­ted to a sin­gle ma­chi­ne vi­sion con­trol­ler

  • Fa­ster pro­cess times thanks to high com­pu­ting power of the ma­chi­ne vi­sion con­trol­ler

  • Sui­ta­ble for very high re­so­lu­tion in­spec­tion tasks

  • Com­pact ca­me­ra de­si­gn



 

Smart Ca­me­ras

  • Image cap­tu­re and eva­lua­tion takes place in the smart ca­me­ra

  • Data out­put via in­te­gra­ted in­ter­fa­ces

  • Op­tio­nal­ly in­te­gra­ted il­lu­mi­na­tion tech­no­lo­gy

  • No ad­di­tio­nal con­trol­ler re­qui­red



 

Ap­pli­ca­tions of Ma­chi­ne Vi­sion Ca­me­ras

Po­si­tion Check

Robot Po­si­tio­ning

Parts Mea­su­re­ment

Qua­li­ty Con­trol

Pre­sen­ce Check

Pro­cess Mo­ni­to­ring

Code Rea­ding

Re­lia­ble So­lu­tion for Cross-​Industry Ap­pli­ca­tions

Au­to­mo­ti­ve In­du­stry

  • Qua­li­ty in­spec­tion of car in­te­rior doors

  • Qua­li­ty in­spec­tion of en­gi­ne blocks

  • Po­si­tion de­tec­tion for au­to­ma­ted tighte­ning

Elec­tro­nics In­du­stry

  • Po­si­tion check of PCBs

  • Chec­king the ali­gn­ment of com­po­nen­ts

  • In­spec­tion of plug con­nec­tors and ca­bles

Pac­ka­ging In­du­stry

  • Check pac­ka­ges for da­ma­ge, con­ta­mi­na­tion or mis­sing la­bels

  • Label in­spec­tion of pac­ka­ging

  • Mi­ni­mum shelf life test on PET bot­tles

Food In­du­stry

  • Orien­ta­tion of be­ve­ra­ge cans 

  • Label check on pac­ka­ging

  • Te­the­red cap in­spec­tion

This Is the Dif­fe­ren­ce Bet­ween Sur­fa­ce and Line Ca­me­ras

The fol­lo­wing table sum­ma­ri­zes the main dif­fe­ren­ces bet­ween sur­fa­ce and line ca­me­ras:

Sur­fa­ce ca­me­ras

Image cap­tu­re of com­ple­te 2D sur­fa­ces (with one cap­tu­re)
High image qua­li­ty
Ideal for sta­tio­na­ry ob­jec­ts
Sui­ta­ble for ge­ne­ral image pro­ces­sing



Line Ca­me­ras

Image cap­tu­re takes place line by line (mo­ve­ment is ne­ces­sa­ry to cap­tu­re the ob­ject)
Image qua­li­ty de­pen­dent on mo­tion and time of image cap­tu­re
Ideal for ap­pli­ca­tions with mo­ving ob­jec­ts and end­less ma­te­rials 
High speed

Ope­ra­ting Orin­ci­ple of CMOS Sen­sors with Glo­bal or Rol­ling Shut­ter

CMOS image sen­sors have two ex­po­su­re me­thods that con­trol how an image is cap­tu­red and read. These pro­ce­du­res de­ter­mi­ne the ex­po­su­re time and thus the amount of light that is con­ver­ted into elec­trons as a value in the ca­me­ra sen­sor. A di­stinc­tion is made bet­ween glo­bal shut­ter and rol­ling shut­ter:

Glo­bal Shut­ter

En­ti­re image area is ex­po­sed si­mul­ta­neou­sly 
Sui­ta­ble for sta­tic as well as dy­na­mic ap­pli­ca­tions
No image di­stor­tion on mo­ving ob­jec­ts

Rol­ling Shut­ter

Lines are ex­po­sed with a time off­set
For sta­tic ap­pli­ca­tions
Image di­stor­tions due to fast ob­ject mo­ve­men­ts (rol­ling shut­ter ef­fect)
Cap­tu­ring still ima­ges 

The Rol­ling Shut­ter Ef­fect

With the rol­ling shut­ter, the ex­po­su­re time is the same for all pi­xels of the sen­sor, but the ex­po­su­re of the in­di­vi­dual lines takes place one after the other with a time delay. The rol­ling shut­ter ef­fect oc­curs when an ob­ject moves fa­ster than the ex­po­su­re and read time, cau­sing the image to be di­stor­ted due to ex­po­su­re.

Left: Glo­bal shut­ter, Right: Rol­ling shut­ter

Mo­no­chro­me or Color Ca­me­ra? Which Do I Use When?

Ac­tual Image

Image Cap­tu­re with a Mo­no­chro­me Ca­me­ra

A mo­no­chro­me ca­me­ra can di­stin­guish ob­jec­ts from the back­ground.

Image Cap­tu­re with a Color Ca­me­ra

A color ca­me­ra is able to di­stin­guish ob­jec­ts from each other and from the back­ground.

In in­du­strial image pro­ces­sing, a di­stinc­tion is made bet­ween mo­no­chro­me and color ca­me­ras. Mo­no­chro­me ca­me­ras cap­tu­re gray­sca­le and focus on the dif­fe­ren­ces in bright­ness in the image. This makes them par­ti­cu­lar­ly sui­ta­ble for ap­pli­ca­tions that re­qui­re fine con­trasts and de­tails, such as when in­spec­ting sur­fa­ces or mea­su­ring ob­jec­ts.

Color ca­me­ras, on the other hand, can cap­tu­re color in­for­ma­tion, al­lo­wing them to cap­tu­re sur­fa­ces more ac­cu­ra­te­ly. They ana­ly­ze the en­ti­re color spec­trum, pro­vi­ding more de­tai­led and ver­sa­ti­le image re­pro­duc­tion. This makes them ideal for ap­pli­ca­tions where color plays an im­por­tant role, such as in pro­duct qua­li­ty con­trol, where color dif­fe­ren­ces can in­di­ca­te ma­te­rial de­fec­ts.

What to Con­si­der When In­stal­ling Ma­chi­ne Vi­sion Ca­me­ras

To en­su­re re­lia­ble image cap­tu­re, the fol­lo­wing in­struc­tions must be ob­ser­ved when ad­ju­sting the in­du­strial ca­me­ra.
In ad­di­tion to the op­ti­mal orien­ta­tion of the ca­me­ra, the po­si­tio­ning of the il­lu­mi­na­tion plays an im­por­tant role. The shape of the ob­ject to be exa­mi­ned is key for how the light rea­ches the ca­me­ra to crea­te the hi­ghe­st pos­si­ble con­tra­st. It is im­por­tant to note, for exam­ple, the angle and the re­sul­ting re­flec­tions. 

The Ma­chi­ne Vi­sion Ca­me­ra In­ter­fa­ce

An Ether­net in­ter­fa­ce for in­du­strial ca­me­ras al­lo­ws image data to be trans­fer­red over a net­work. This in­ter­fa­ce is com­mon­ly used in in­du­strial image pro­ces­sing to con­nect ca­me­ras to ma­chi­ne vi­sion con­trol­lers or other de­vi­ces.

Gi­ga­bit Ether­net (GigE)

Gi­ga­bit Ether­net (GigE) is an Ether­net tech­no­lo­gy that ena­bles data trans­fer rates of up to 1 Gi­ga­bit per se­cond (1 Gbit/s). The main fea­tu­res of Gi­ga­bit Ether­net in con­nec­tion with in­du­strial ca­me­ras are:
 

  • Fast trans­fer of large amoun­ts of image data

  • Easy in­te­gra­tion thanks to pro­to­col stan­dard

  • Mul­ti­ple ca­me­ras can be ope­ra­ted in a net­work


It is also pos­si­ble to con­nect the ma­chi­ne vi­sion ca­me­ra via a cable using PoE (Power over Ether­net), which means that both power sup­ply and data trans­fer take place via a sin­gle con­nec­tion.


Re­so­lu­tion

The spa­tial re­so­lu­tion of a sen­sor in­di­ca­tes the num­ber of pi­xels: the hi­gher the re­so­lu­tion, the smal­ler the pixel size and the finer the de­tails that can be de­tec­ted. Sen­sors can have dif­fe­rent re­so­lu­tions with the same di­men­sions be­cau­se the pixel size can vary. 

Frame Rate

The frame rate in­di­ca­tes the num­ber of com­ple­te fra­mes a ca­me­ra cap­tu­res per se­cond. A hi­gher frame rate ena­bles many ima­ges to be cap­tu­red in fast-​paced ap­pli­ca­tions.

Ex­po­su­re Time

The ex­po­su­re time de­ter­mi­nes how much light falls on the CMOS sen­sor and thus af­fec­ts the bright­ness and shar­pness of the re­cor­ded image. A lon­ger ex­po­su­re time leads to brighter ima­ges, but can also cause mo­tion blur and in­crea­sed image noise. A short ex­po­su­re time ena­bles fast ap­pli­ca­tions and re­du­ces the as­so­cia­ted mo­tion blur. 

The Right Re­so­lu­tion for Every Ap­pli­ca­tion

Re­so­lu­tionAc­cu­ra­cyExam­ples
1.6 MPAp­pli­ca­tions that do not re­qui­re ex­tre­me­ly high re­so­lu­tionOp­ti­cal cha­rac­ter re­co­gni­tion, as­sem­bly con­trol, pre­sen­ce check
5 MPAp­pli­ca­tions re­qui­ring me­dium level of de­tailIn­spec­tion of pac­ka­ging
12 MPAp­pli­ca­tions re­qui­ring high pre­ci­sionIn­spec­tion of fine me­cha­ni­cal parts
24 MPAp­pli­ca­tions re­qui­ring very high re­so­lu­tion and at­ten­tion to de­tailChec­king PCBs for faul­ty com­po­nen­ts
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