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Contrast Sensor Technology

Con­trast sen­sors de­tect con­trast and color dif­fe­ren­ces on a wide range of ma­te­rials and sur­fa­ces. They can ac­cu­ra­tely de­tect the po­si­tion of con­trast mar­kings even at high ma­chi­ne speeds. With white light LED or red laser light, con­trast sen­sors re­liably de­tect print marks and ob­jects based on dif­fe­ren­ces in con­trast.
Mode of Operation
Light
Color Spaces
Reflective Properties
Technology
Industries
Teach-in
Çıkışlar
Montaj

How Do Con­trast Sen­sors Work?

Con­trast sen­sors are pho­to­elec­tro­nic sen­sors that work ac­cor­ding to the prin­ci­ple of a re­flex sen­sor: Emit­ted light is re­flec­ted by the ob­ject, re­ab­sor­bed and eva­lua­ted. Con­trast sen­sors are used to de­tect mar­kings based on dif­fe­ren­ces in con­trast. They are cha­rac­te­ri­zed by high swit­ching speeds and low jit­ter. Dif­fe­rent con­trast de­tec­tion tech­no­lo­gies are avai­la­ble to achie­ve the best pos­si­ble de­tec­tion:
 
  • Laser red light + mo­no­chro­me pho­to­dio­de
  • White light + mo­no­chro­me pho­to­dio­de
  • White light + RGB pho­to­dio­de


What Is the Dif­fe­ren­ce Bet­ween Light and Laser Light?

Light con­sists of elec­tro­mag­ne­tic ra­dia­tion vi­si­ble to the human eye that pro­pa­ga­tes in dif­fe­rent wa­ve­length ran­ges when emit­ted by a light sour­ce. Laser light is crea­ted by sti­mu­la­ted emis­sion that am­pli­fies light, i.e. high con­cen­tra­tions of rec­ti­fied light waves are bund­led into a beam.

What Is a Color Space and Which Is Par­ti­cu­larly Re­le­vant for Sen­sors?

A color space is a de­fi­ned color coor­di­na­te sys­tem used to sys­te­ma­ti­ze and stan­dar­di­ze co­lors. This de­ter­mi­nes the amount of co­lors and the method of color re­pre­sen­ta­tion. In a color space, co­lors are des­cri­bed by coor­di­na­tes where the axes re­pre­sent dif­fe­rent color pro­per­ties, such as color in­ten­sity, bright­ness, tone or sa­tu­ra­tion. The RGB and CMYK color spa­ces are par­ti­cu­larly re­le­vant for in­dustry. The RGB color space is used for sen­sors, be­cau­se they co­llect color in­for­ma­tion in the form of red, green and blue color chan­nels.

 

RGB Color Space

RGB uses light to crea­te co­lors by com­bi­ning red, green and blue.

CMYK Color Space

The CMYK color space is mainly used in prin­ting and pro­du­ces co­lors with cyan, ma­gen­ta, ye­llow and black.

What Is White Light Based on the RGB Color Space?

The RBG color model works as an ad­di­ti­ve color mix. White light is crea­ted by mi­xing red, green and blue light. Black re­sults in the ab­sen­ce of light of any wa­ve­length. 
 

What Are the Re­flec­ti­ve Pro­per­ties of Co­lo­red Sur­fa­ces?

Con­trast Sen­sor Tech­no­lo­gies

How Do Con­trast Sen­sors with White Light Work?

Con­trast sen­sors with white light LED emit white light in the form of a rec­tan­gu­lar light spot that is re­flec­ted back from the sur­fa­ce to the re­cei­ver of the sen­sor, which then eva­lua­tes this light.

Re­cei­ver with RGB Pho­to­dio­de (P1PWxxx)

The re­cei­ver con­sists of three areas co­rres­pon­ding to the RGB color space. De­pen­ding on the color of the con­trast mar­king, the light is re­flec­ted back to the re­cei­ver ac­cor­ding to the re­flec­tion pro­per­ties and eva­lua­ted based on the three chan­nels.

Re­cei­ver with Mo­no­chro­me Pho­to­dio­de (WM03xxx)

The pho­to­dio­de of the re­cei­ver con­sists of a sin­gle con­ti­nuous sur­fa­ce. De­pen­ding on the color of the con­trast mar­king, the light is re­flec­ted back to the re­cei­ver ac­cor­ding to the re­flec­tion pro­per­ties. The re­cei­ver eva­lua­tes the re­cei­ved bright­ness and sorts it into a grays­ca­le.

How Do Con­trast Sen­sors with Laser Light Work?

Con­trast sen­sors with laser light emit a spot of red laser light, the re­flec­tion of which is eva­lua­ted by the re­cei­ver. The re­cei­ver uses a mo­no­chro­me pho­to­dio­de. Con­trast sen­sors with laser light are avai­la­ble in a di­gi­tal and an ana­log ver­sion:

  • Di­gi­tal ver­sion (YM24PAH, YP11VAH): The swit­ching th­reshold is set to a cer­tain bright­ness level. This bright­ness value is then com­pa­red with the amount of light re­flec­ted by the ob­ject.
  • Ana­log ver­sion (YP11MGV): The ana­log out­put out­puts a vol­ta­ge pro­por­tio­nal to the bright­ness. The out­put vol­ta­ge in­crea­ses along with the de­gree of bright­ness.

Technology Comparison of Contrast Sensors with Laser Light and LED White Light

LED white light Laser Light (red)
Near field up to 50 mm Dis­tan­ces up to 150 mm
Print and color mark de­tec­tion De­tec­tion of con­trast dif­fe­ren­ces
Very high speed up to 50 kHz High speed up to 20 kHz
Rec­tan­gu­lar light spot Small, round light spot


Contrast Sensor Applications

Checking the Material End with Visual Marks

Film material is processed on rolls in production technology. During production, the material is unwound from the roll. Marking stripes are applied to mark the end of the roll. These are detected by contrast sensors to ensure that a roll change is initiated in good time.

Color Check of Objects

To ensure high product quality, the visual characteristics must also be monitored and controlled at all times in the production process. Contrast sensors can detect differences in color, enabling quality control based on visual appearance characteristics. For example, the color of bottle caps is checked to ensure that the correct caps are always used in a container.

Print Mark Recognition

Print marks are colored markings or gray blocks in various percentages printed on packaging materials. They can be recognized photoelectronically and then trigger control commands on a connected processing machine. Print marks are used to control various processes:

  • Alignment and positioning of objects
  • Cutting, welding and bonding processes

Detection of Contrast Differences

Contrast differences are different brightness levels of objects. Brightness levels are compared with reference values to solve various applications:

  • Differentiation of objects based on contrast values
  • ​​​​​Presence check of inserts in an assembly process
  • Presence check of very flat objects against a background

Checking the Material End with Visual Marks

Film material is processed on rolls in production technology. During production, the material is unwound from the roll. Marking stripes are applied to mark the end of the roll. These are detected by contrast sensors to ensure that a roll change is initiated in good time.

Color Check of Objects

To ensure high product quality, the visual characteristics must also be monitored and controlled at all times in the production process. Contrast sensors can detect differences in color, enabling quality control based on visual appearance characteristics. For example, the color of bottle caps is checked to ensure that the correct caps are always used in a container.

Print Mark Recognition

Print marks are colored markings or gray blocks in various percentages printed on packaging materials. They can be recognized photoelectronically and then trigger control commands on a connected processing machine. Print marks are used to control various processes:

  • Alignment and positioning of objects
  • Cutting, welding and bonding processes

Detection of Contrast Differences

Contrast differences are different brightness levels of objects. Brightness levels are compared with reference values to solve various applications:

  • Differentiation of objects based on contrast values
  • ​​​​​Presence check of inserts in an assembly process
  • Presence check of very flat objects against a background

In­dus­tries for Pre­fe­rred Use of White Light LED Con­trast Sen­sors

Pac­ka­ging In­dustry

Con­trast sen­sors with LED white light are used for print mark re­cog­ni­tion in the pac­ka­ging in­dustry.

Gıda endüstrisi

LED beyaz ışıklı kon­trast sensörleri, gıda endüstrisinde baskı işaretlerinin algılanmasında kullanılır. 

Baskı endüstrisi

Beyaz ışıklı LED kon­trast sensörleri, baskı endüstrisinde çok çeşitli baskı işaretlerini algılar.

Lazer ışıklı kon­trast sensörlerinin ter­cih edi­len kullanımı için sektörler

Oto­mo­tiv endüstrisi

Lazer ışığına sahip kon­trast sensörleri, oto­mo­tiv endüstrisinde kon­trast algılaması için kullanılır.

Plas­tik endüstrisi

Plas­tik endüstrisinde kon­trast algılaması için lazer ışığına sahip kon­trast sensörleri kullanılır.

Kon­trast sensörlerinin uy­gu­la­ma­ya tanıtılması nasıl çalışır?

Lazer ışığına sahip kon­trast sensörlerinde ayar po­tan­si­yo­me­tre ile yapılır. Yani eşik değeri ma­nuel ola­rak ayarlanır.

Beyaz ışık LED'li kon­trast sensörleri, tuşa basılarak tanıtılır. Sensör, teach-​in anahtarıyla anah­tar­la­ma eşiğini oto­ma­tik ola­rak he­sa­plar. Bunun için iki farklı tanıtma modu mev­cut­tur:
  • İki noktalı teach-​in: İki noktalı teach-​in'de bir tanıtma işleminde ob­je­ye, yani mar­ka­ya ve başka bir tanıtma işleminde arka plana tanıtılır. Sensör, be­lir­le­nen ve kay­de­di­len iki ölçüm değeri arasında anah­tar­la­ma noktasını, iki teach-​in noktası arasında ola­cak şekilde he­sa­plar.
  • Di­na­mik teach-​in: Di­na­mik teach-​in'de sensör, oto­ma­tik teach-​in'i mümkün kılan bir kayıt mo­du­na alınır. Bu modda ölçülen değerler kay­de­di­lir. Kayıt modu sona er­dik­ten sonra mi­ni­mum ve mak­si­mum ölçülen değerler arasında bir anah­tar­la­ma noktası hesaplanır.

Çıkışlar ve arayüzler

Di­ji­tal anah­tar­la­ma çıkışı

Di­ji­tal bir anah­tar­la­ma çıkışı üzerinden kon­trast değerleri teach-​in veya po­tan­si­yo­me­tre ile tanıtılabilir. Tanıtılan kon­trast değerine ulaşıldığında, sensör çıkışta bir anah­tar­la­ma sin­ya­li gönderir, bu sa­ye­de de örn. kon­trast veya baskı işaretleri algılanabilir.

Ana­log çıkış

Bir ana­log çıkış üzerinden kon­trast değeri doğrusal orantılı akım (4…20 mA) veya ge­ri­lim değeri (0…10 V) ola­rak ve­ri­lir. Bu sa­ye­de aydınlık se­yir­le­ri tam ola­rak de­netle­ne­bi­lir.



IO-​Link

IO-​Link tek­no­lo­ji­si, sensörler ve aktüatörler ile dünya çapında stan­dart iletişim için kullanılmaktadır. Bu bir nok­ta­dan nok­ta­ya iletişimdir.




 

Kon­trast sensörleri için mon­taj talimatları

Sensör, baskı işaretine pa­ra­lel ola­rak hizalanır.

Par­lak ob­je­ler­de sensör öngörülen açıda monte edi­lir.

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