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How to detect and position different foils on changing background
Article No: KA-09228
Version: 1.0
Subject to change without notice
Detect and position different foils (color and translucence) on changing background by using IO-Link or the external digital sensor input.
Related Products
KTS-WB9134115AZZZZZZZZZZZZZZZ1
CSS High Resolution
KTS
Table of Contents
General Application Description
The task in this application was to detect and position two different foils on a changing background.
The background itself is a conveyor, consisting of metal plate parts attached to chains. Due to the fact the aim of the application is to laser cut the foils, the laser leaves marks on the conveyors metal plates in every process cycle. The left marks are placed non-deterministic and variate in color and shape.
Speaking about the foils, one is slightly translucent, has a white color and is about 0.5 mm thick, the other one is not translucent, has a dark gray color and is about 3 mm thick.
The machine workers task is to place and position the foils on the conveyor before the laser process starts. To ensure the correct position and presence of the foil, sensors are used.
Pictures of Background and Foils
Requirements and Challenges
The requirements were a positioning below 1 mm and a reliable detection of both foils undependably of the current background. The challenge here are the different properties of the foils and differences in contrast of the background for each process cycle. Because of mechanical reasons, the sensing distance had to be > 35 mm and < 200 mm.
First try was to use a AS30 with 100 mm sensing distance. Due to the occurring brown lines in the background, the AS30 can -in some cases- not differentiate between the foils edge and such line/groove, especially if the contrast of the groove matches the foils contrast.
Solution
Because of the difficult background condition, the idea was to teach-in the background right after the conveyor stops in a process cycle. This requires a sensor which has a small light-spot and provides a one-point-teach-in. The chosen sensor is a KTS Prime using its color mode (evaluation in RGB). In detail, the KTS-WB9134115AZZZZ (p/n 1220673) is used.
The sensor provides a sensing distance of 40 mm with the light-spot dimension of 3.9 mm x 0.9 mm. There are two possibilities to perform the teach in after each process cycle:
Using the IO-Link interface The one-point-teach-in can be performed using the corresponding ISDU. This method has the advantage to be more flexible, because other sensor function can be written or read out as well. The switching output of the sensor can be read out via IO-Link as well. Changes of the sensors setting can be done from remote.
Using the digital sensor input The sensor can be configured to perform a one-point-teach-in when the signal at the input pin is true. This is the fast and easy way.
However, because of the flexibility, the customer uses the IO-Link interface.
Final Process:
Conveyor stops after the last machine cycle
The PLC does perform a teach-in via IO-Link
The KTS "learns" the current background (can be shiny metal, a groove,...) using the color mode.
The worker is positioning the foil and gets a visual signal when the foil is in the right position. So, the sensor recognizes any difference in contrast, which is the signal that there must be a foil and switches the output.
The woker starts the next machine cycle...
Other Possible Solutions
Color Sensor: CSS High Resolution (50-150 mm) The CSS HR was able to "learn" the optical properties of the used foils and differ it from any background. It was not used because of the round light-spot with ~ 4 mm diameter as well as the necessary teach procedure if the foils change somehow (other types, different color,...).
Energetic laser sensors, for example the KTM-L (mini contrast sensor with laser) and IO-Link This requires the usage of the IO-Link interface. The raw contrast value (mostly part of the process data) can be compared after the conveyor stops and placed foil. If the value changes more than +- X %, a foil is placed. It was not used because of the single value and possible wrong signals if the backgrounds contrast matches the foils contrast. For other applications, this might be a suitable and cheap solution. Some kind of control unit is required.
