Material Agnostic Fiber Optic Web Edge Sensor

ARIS Web Position Sensor uses a revolutionary web edge sensor technology based on fiber optics to accurately determine the position of a web material irrespective of its material properties. This sensing principle is unique and provides a true, absolute web position measurement. The working principle of the web position sensor is as follows. Light from an array of infrared LEDs (or laser diodes) is projected on to the web surface. The light that intercepts the web get scattered in all direction and this scattered light is spatially filtered using the fiber optic elements within the sensor. The filtered light is then projected on to a camera sensor. The web position is determined by processing the output of the camera sensor using sophisticated digital signal processing algorithms in real-time.

Sensor Specification
Two web position sensor widths that are currently available are 16 mm and 48 mm (see Fig. 1).

sensorspecificationsensorspecification
Figure 1: The two sensor options with 48 mm (left) and 16 mm (right) sensor.

The sensor head includes an infrared filter, a spatial filter based on fiber optics, a camera sensor and infrared light source. The camera sensor has a resolution of 63.5 micron with 256 or 768 pixels based on sensor width. The infrared LEDs have a peak wavelength of 850 nm.
Because of the computational complexity the signal from the camera sensor needs to be processed with a dedicated sensor processing unit which is located remotely from the sensor head. Up to 5 m long cable can be used with the sensor head enabling remote installation of the sensor head from the web sensor processing unit.

Sensor Performance: Experimental Procedure
The working principle of the web sensor enables it to detect any type of material without any calibration. In this white paper we shown experiments with four type of materials (see Figs. 2 – 5) to highlight the web sensor’s ability to work with different materials. These materials include a (1) a low basis weight nonwoven web that is highly porous, (2) an optically black nonwoven web with low optical properties, (3) a clear film with low opacity, and (4) burlap a textile material which is significantly porous. All these materials are troublesome to existing sensing technologies since the amount of signal attenuation is significantly affected by the material properties.

Nonwoven Material Sample
Figure 2: A low basis nonwoven web material (Nonwoven Sample 1).

Black Nonwoven with low optical propertiesNonwoven Material Sample
Figure 3: Optically low reflective black nonwoven web material (Nonwoven Sample 2).

Transparent Film with low opacity
Figure 4: Optically transparent clear film web material.

Burlap
Figure 5: Porous burlap web material.

An experimental setup (see Fig. 6) equipped with a high precision motor stage which moves the web material back and forth is used to quantify the sensor performance.

High precision motor stage and sensor mount
Figure 6: High precision motor stage with a c-shaped fixture to hold the web material.
A sensor mount with an option to mount 16 mm and 48 mm sensor at a working distance of 10 mm and 20 mm.

The sensor is mounted on the experimental setup with an ability to change the working distance.
Even though the sensor is design to work with web materials at an ideal working distance of 8 mm to 12 mm, the work distance is increased to 20 mm to understand the performance of the sensor. A set of experiments were conducted with each web sample. The web on the motor stage was moved back and forth (as shown in Fig. 7) several times during a experiment while recording the motion and sensor edge position data.

Experimental procedure graphed results
Figure 7: Experimental procedure where the web mounted on the c-shaped fixture is moved back and forth several times with a constant velocity.
The abscissa shows time in seconds and ordinate shows the sensor measurement in mm.

Figs. 8 – 11 show representative sample of experimental results with 16 mm sensor for the four different web materials. Sixteen sets of data were collected by positioning the motor stage to move back and forth eight times. The step size and the motor speed was chosen
such that every single pixel is covered during every experiment. Data from all sixteen experiments are superimposed into a single plot. The abscissa shows the web displacement measured using the motor position sensor and the ordinate shows the web edge measured using our web guide sensor. Both the axes are represented in millimeters. The blue dots in the plots are the actual measured data and the green lines are the linear fit for each set of experiment.

Results with optically transparent web material
Figure 8: Results with low basis weight nonwoven (Sample 1).
Average Slope - 1.023553725; Average Bias - 0.05354163867; Average R2 - 99.72041439%.
The results show excellent precision and accuracy of the sensor.

 Summary of results for low basis weight nonwoven
Figure 9: Results with black nonwoven (Sample 2).
Average Slope - 0.9937519759; Average Bias - 0.05990121766; Average R2 - 99.59770173%.
The results show excellent precision and accuracy of the sensor.

Summary of results for black nonwoven
Figure 10: Results with optically transparent web material.
Average Slope - 0.9988831702; Average Bias - 0.08919115346; Average R2 - 99.94256119%.
The results show excellent precision and accuracy of the sensor.

Summary of results for burlap
Figure 11: Results with porous web material.
Average Slope - 1.111496044; Average Bias - 0.07965415279; Average R2 - 99.55181116%.
The results show good precision and accuracy of the sensor.

All the experiments showed excellent precision and accuracy of the sensor and sensing principle. Experiments were also repeated for 20 mm working distance and the results from all the experiments are summarized in Figs. 12 – 15.

 Summary of results for low basis weight nonwoven
Figure 12: Summary of results for low basis weight nonwoven (Sample 1) at 10 mm and 20mm working distance.

Summary of results for black nonwoven
Figure 13: Summary of results for black nonwoven (Sample 2) at 10 mm and 20 mm working distance.

Results with optically transparent web material
Figure 14: Summary of results for optically transparent at 10 mm and 20 mm working distance.

Summary of results for burlap
Figure 15: Summary of results for burlap at 10 mm and 20 mm working distance

Conclusion

The experimental results show the accuracy and precision of the web sensor is unaffected by the material properties unlike conventional web guide sensors. The sensor accurately measures the edge position with opaque material, porous web material, nonwoven web materials, transparent web material. Similar results are also seen with the 48 mm sensor and with other materials such as paper, plastics, foil and films.

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