Electricity + Control August 2017

round up

CONTROL SYSTEMS + AUTOMATION

Why use a colour mark sensor with RGB technology?

Is it true that processing time for the colour mark sensor af- fects speed? Speed is more of an issue for a true colour sensor rather than a colour mark sensor. The R58E from Banner can perform 10 000 actuations per second, which is very fast! Why does Banner’s R58E colour mark sensor use the red, green, and blue combination of LED colours? The R58E uses this combination so that it can reliably sense virtu- ally any registration mark/background combination. The RGB (red, green, and blue) combination can be combined to create almost any colour. Your computer monitor, for example, which is capable of millions of colours, uses RGB technology. The R58E, using these three colours, is able to determine the colour of the registration mark and the colour of the background. The sensor will then use the LED that provides the best contrast between the registration mark and the background. How do I pick the right LED colour for my application? With the R58E, you do not need to choose an LED colour. The R58E selects the proper LED colour automatically during the initial TEACH function. However, when using a monochromatic colour mark sensor, resources such as colour selection charts are used to select the proper LED colour. How do I switch between the different LED colours? You don’t need to manually switch LEDs. The R58E will automati- cally select LED colours during the TEACH function. Can I choose the LED colours in the R58E? No. The R58E comes with only the possibility of three LED colours: red, green and blue. Does having 3 LED colours affect the sensor’s response time? No. After the initial TEACH process, the R58E’s response time is the same as comparable registration mark sensors. The R58E has a 50 microsecond response time, which allows 15 microsecond repeatability. How do I sense a registration mark on clear material? Clear materials (e.g. a clear poly web) do not reflect light very well, so when sensing a registration mark on a clear material, position a reflective surface directly behind the clear material to return light to the sensor. The registration mark will block the light from reaching the reflective surface and will be detected by the sensor. To avoid the shine from clear materials, you might consider mounting your sensor at a 15° skew angle. How can I maximise sensing in my high-sensitivity applica- tions with the R58E? Use the dynamic TEACH function to teach the sensor a series of conditions on the fly. The R58E takes multiple samples of a regis- tration mark against its background and is able to automatically set the sensitivity at the optimum level. Enquiries: BrandonTopham. Email brandon.topham@retautomation.com

What is the difference between a true colour sensor and a col- our registration mark sensor? True colour sensors can be taught to detect minute colour differ- ences (for example, tell dark blue from black), while colour mark sensors detect a grayscale change in colour. True colour sensors, like Banner ’s QC50, reflect light off a target using a white LED and red, green and blue filter elements. A colour value is then assigned to the light returning to the sensor based on the amount of light reflecting off the target. With colour mark sensors, the sensor uses just a LED and no filters. The sensor distinguishes the target colour based on how it contrasts with the background colour. Not always. A large number of colour sensing applications can be done quite effectively by detecting a grayscale change in the colour mark. In these instances, we recommend using a colour mark sen- sor like the R58E, especially in high-speed applications. A true colour sensor is required when sorting out targets that differ only in colour; for example, when you need to distinguish between light blue and dark blue. However, when distinguishing a registration mark on a constant background, a colour mark sensor is your best choice. What is the difference between a colour mark sensor and a registration mark sensor? There is no difference; these terms are synonymous. What does 16 grayscale contrast levels specification mean? One way to spec a colour mark sensor is to understand how many levels of grayscale it can detect. The finer the sensor’s resolution, the more levels can be detected. A commercial grayscale printer’s chart is divided into 20 segments ranging from black to white, and the shades of gray between. Many sensors are able to detect the first 16 segments starting at white. Does Banner’s R58E have a spec for grayscale contrast levels? The R58E can easily meet the spec for 16 levels of grayscale. Because of the combination of RGB LEDs, the R58E’s resolution capability far exceeds grayscale charts. The R58E’s capability for subtle contrast changes far surpasses the specification for 16 levels of grayscale. Isn’t it better to use a true colour sensor rather than a colour mark sensor?

8 Electricity + Control

AUGUST 2017