A small collection of OCT application from practice

ihenseler

The micrometer-accurate insight into films is used to measure the thickness of individual layers in multilayer films or to check their completeness. Using the OCT method, layer thicknesses are measured, the bonding between layers qualified and also micro holes, brows or particles are localized.

flo-ir

berührungslos messen

Aawasserstrasse 10

CH – 6370 Oberdorf

Schweiz

Tel.: +41-41 871 39 88

Fax: +41-41 871 39 87

E-Mail: info@flo-ir.ch

A small collection of OCT

applications from practice

Measuring the thickness of the side wall of a coffee capsule, the width

of a seal seam, the layer thicknesses in a multi-layer plastic film and

location of microholes in a peel-off cover.

The micrometer-accurate insight into films is used to measure the thickness of

individual layers in multilayer films or to check their completeness. Using the OCT

method, layer thicknesses are measured, the bonding between layers qualified and

also micro holes, brows or particles are localized.


Seite 2

Measuring the flight time of light

An image of the flight time of light measurement method consists of 300 * 300 axial

interferograms which touch each other laterally. The method is used to compare the

flight time of reflected (or scattered) photons from the object surface or layers

between two surfaces with the reflection of the same light from the same source in a

reference beam.

The interferograms from the measuring arm and the reference arm produce a linear

pattern of different brightness. The relative optical path is mapped as an axial depth

profile.

In the OCT method, transversal resolution is decoupled from the resolution in the z

direction, which allows to record tomograms in real time with a resolution in the z

direction in micrometer accuracy.

The transversal resolution is determined by the numerical aperture of the optics, but

the spatial resolution in the depth of the material depends on the spectral width of the

light source used for the measurement.

On the ASP array (Active Sensor Pixel), 300 x 300 "interferometers" are built on a

CMOS. Each pixel on the chip is equipped with its own lens and its own signal

preprocessing. The ASP- array captures 1 million two-dimensional images per

second.

Above:

The OCT-DUAL measuring head in the

round table system. The system is

equipped with the basic software and

with customer- specific software.

Right:

Complete measuring cell with automatic

measurement of all kind of components.

In the data acquisition, a stack of up to 500 images in z direction is collected. The

distance of the images in the z direction is determined by the deflection of the

reference mirror of the linear drive as well as by the light source (coherence

length).

By default a linear drive with a resolution of 100 nm is used for the step width in z

direction. More exact depth resolution require a higher resolution of the axis and

an optimized light source.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 3

Layer by layer

The thickness of individual layers in multilayer films can only be measured with

special optical methods. Optical methods also provide the thickness of each

individual layer in a film composite at high production speeds and in the case of

flapping films.

Extruder systems produce monofilms or films consisting of several layers with

more than 200 m / min. The functional layers are aimed at achieving a higher gas

tightness with simultaneously higher mechanical strength.

In order to minimize the use of the material, but to ensure the functions,

manufacturers are forced to produce films of ever smaller thickness and highest

precision. The thickness of clear lacquer layers or of adhesion- glue layers are

required quality criteria for coatings, which must be checked and proven.

Although conventional, capacitive sensors are robust and are therefore still

used in blown film systems, they have significant disadvantages:

They only work with contact.

Only the total thickness is measurable.

Selective measurements in multi layer films are not measurable.

The measured values react sensitively to temperature variations.

Each layer of a composite system usually consists of a defined material, which

differs from the following material. The materials have different optical densities

(boundary layer, adhesive layer, gas barrier layer), which is reflected by a

difference in refractive index. At each layer transition, a clear difference in the

flight time of the photons is determined at the boundary layer between two films,

which is used for the exact measurement of the thickness.

The advantages of the OCT method are :

Completely non-contact measurement of monolayers or transparent, resp.

Half-transparent layers which consist of several layers.

Accuracies also with moving objects in the sub-μm range.

Measurement by comparison of the measured signal with the reference signal.

Measurement of optically cloudy materials.

automatically adjustable working range up to a few cm in front of the sensor.

High sampling rate (several kHz) of the information in the z direction (depth).

wide independence against vibrations.

Independent of the surface of the material to be measured.

No influence of the color of the object.

Missing each film also in films consisting of several layers.

In the industrial production environment, the working distance between the sensor

and the measuring object often varies several mm in a frequency rate of several

Hz. Despite this frame condition, the sensor measures the thickness of a film layer

more precisely than 1 μm because mechanical movements are very slow

compared to the speed of the light.

The integration of the OCT measuring method results in a added value for

manufacturers co extrudered films and coating systems by simple retrofitting.

online measurement

automatic quality management

Throughput speeds up to several 100 m / min

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 4

Provision of feedback signals for the process control circuits.

Integration of the SPC (Statistical Process Control)

Basic Windows 10.IOT

With the aid of the measuring system, the layer thicknesses or changes in the

layer thicknesses can be detected and corrected as required, which results in

considerable commercial advantages:

Reduce the layer thickness

Reduce material costs

Increased productivity

Guaranteeing the highest quality standards.

The measured data are available via various output interfaces. The output logs are

defined by the customer and the connection to an existing process technology is

ensured.

Technical information about the sensor:

We are designing single-station systems as well as DUAL-measuring head

systems and systems for measuring the thickness along the production width.

For test measurements in our house we work in the first phase with a point

resolution of 10 μm and with a step width in the z direction of 1 μm.

Point size (lateral resolution)

From 1 μm to 100 μm

Image Size (Full Image)

From 0.2820 μm * 0.2920 μm

Up to

28.20 μm * 29.20 μm

Light source

830 nm (+/- 10 nm) and Options

Number of pixels 300 * 300

Number of images per image stack 500

Number of frames per second

1'000'000 (ASP array camera)

Table of the PCT- systems we offer in the market:

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 5

Examples from our practice:

Complete measurement of coffee capsules:

In addition to the geometry of the coffee capsules, their wall thicknesses are often

also of tnterest or the thickness of the bottom, because conclusions, influenced from

the collected data, are to detect failure production as early as possible in the

production process. The standard software program measures the diameters and

heights, checks the flatness and the parallelism of individual planes. For the

measurement of freshly produced coffee capsules we offer two machine types in the

market. The station with a rotative disc (picture left) operates with twoa DUAL camera

with a arm length of 135 mm. The portal system (picture right) operates with a panel

in the format of 600 mm * 800 mm.

Both systems are of Swiss made and consist entirely of "Made in Switzerland"

components.

In the OCT pictures, noncentric

shapes, deviations in

flatness or differences in the

thickness of the material are

recognized immediately.

The image on the left shows

a shifted tool.

The picture on the right

shows, that the planarity of

the sealing seam is bad.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 6

Measurement of the side wall thickness in a coffee capsule:

During the production of coffee capsules, the side wall is tapered by the molding

process and is partially thin. Therefore it is of interest that, in addition to the geometry

of the capsule, the thickness of the side wall and possibly also the thickness of the

gas barrier layer in the side wall should be measured too. In the following pictures,

the measurement process is explained using the OCT method at vertically oriented

planes.

Side wall tool in the parking position

Side wall tool in operation

Operation principle

Outer contour

of a capsule

Inside contour

of a capsule

Signals seen from outside

Signals seen from inside

With the additional optical component, the light front is directed via prisms to the

outer wall and to the inner wall of the capsule. Due to the horizontal displacement,

the distance to the surface is measured in the form of an interference. The wall

thickness of the component at the measuring location is extracted from these signals.

The side wall measurement tool is automatically loaded from the parking position and

calibrated. After the measurement has been carried out, the component is also

moved back into the parking position.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 7

Measurement of the individual layers of a coffee capsule:

The optical component is "slipped" over the side wall of the capsule so that the side

wall lies between the horizontally oriented prisms and can be illuminated from both

sides with the measuring light at same time.

Interference occurs at the points where a material transition takes place, which are

shown as distinct peak in the signal. From these interferences, the thickness of the

film results in the horizontal direction and also reveals layer transitions in the interior

of the film.

OCT image of the measurement of a gas barrier layer with the corresponding image

of the measurement with the microscope. (Picture left) The picture shows the

individual layers in the capsule film. (Total of 7 layers)

Layer 1

Layer 4

Layer 7

Layer 2

Layer 6

Layer build-up of plastic hoses or plastic containers:

Layer 3 Layer 5

Whether the finest hoses or inside coated plastic containers, the times when the

parts have been cutted open inspected under the microscope for quality assurance

are finally over.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 8

The two following images show a cross-section through a multilayer cylindrical tube

in the normal image (left) and the OCT image. The OCT image shows that the tube

wall consists of 3 layers. In the same measuring process, the outside diameter and

the thickness of the individual layers are measured.

Thickness Layer 1

Thickness Layer 2

Thickness Layer 3

Layer separation in a film construction:

The delamination of layers in the interior of containers or hoses is hardly noticeable

with conventional systems. The following OCT image clearly shows the delamination

of an inner layer from the substrate, a result which has been completely collected

nondestructively by the OCT method.

Delamination of two layers

Inside layer thickness

Outside layer thickness

In the same measuring process, the thicknesses of each individual layer in the plastic

film are also measured in micrometer- accuracy. Compared to conventional methods,

the OCT method provides signals to differences in the refractive index, which always

leads to a clear signal when a delamination is in play.

The refractive index of air is 1 and the refractive index of plastic is in the region of

1,5, that is a big difference. Diffferences in the refractive index of 0,002 can be

measured by optical coherence tomography systems.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 9

Uneven and non-parallel sealing surfaces:

In the next example, a food tray is shown. The normal image (left) the image of the

gas barrier layer (center) and the color-coded 3D height image (right). From such

measurement data, unevenness in the victor's life is quickly and reliably detected and

measured micrometer-accurately.

Photo of a thermal

formed cup

Thickness of the gas

barrier layer

Geometrical shape of the

thermal formed cup

Overall thickness

Hight difference in

µm compared with

the reference hight

Hight difference in

µm compared with

the reference hight

Hight difference in

µm compared with

the reference hight

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 10

Geometry of Microfluidics components

Microfluid modules are state-of-the-art mixing consoles and laboratory systems in a

very small space. The chips are made of glass or plastic and therefore meet all

requirements for good optical transparency, biological compatibility and chemical as

well as thermal resistance. The following OCT images show 3, respectively, 2

microchannels in such a chip. The geometry of the channels, contents in the

channels or topographic structures can be measured with the OCT method from the

outside with a resolution in the sub-micrometer range.

The graph above shows the width of the

microchannels in micrometers. The entire volume

in the microchannel is precisely measured using

the OCT system. The throughput volume can be

derived from the simultaneous measurement of

the particle speed.

The width of the microchannels as well as their depth or the speed of the medium or

the structures inside the modules, phase changes or material properties can be

reliably determined from the outside with the OCT technology. The OCT images,

which are of interest, can be extracted and analyzed from a recorded stack.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 11

Crack or scratch?

Subsequently, images from an entire image stack are displayed. From Fig. 59

(outer surface) to Fig. 51 (inner side at the measuring site), differences in refractive

index can be analyzed in micrometer steps.

Image 59 Image 58 Image 57

Image 56 Image 55 Image 54

Image 53 Image 52 Image 51

Volumenscan at a step distance of 6 micrometers. Microcracks and air inclusions,

brows or broken edges on the object appear clearly in the OCT picture. The OCT

method presents differences in refractive indexes and not in reflected gray values,

that is one of the most important adventages of OCT method!

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 12

Microcracks in a thermoformed shell

In the case of microcracking, the light radiation from the air enters the material and

shows the difference in the refractive index between the air (1) and the material (1.5

and larger). If a crack in the material is the same light transition, i. The crack

becomes clearly visible. With the OCT camera, 1 million two-dimensional images

with an image distance of a few micrometers are recorded as image piles at the

point of interest.

In the OCT method, the lateral resolution is decoupled from the resolution in the z

direction. The system detects differences in refractive index only. Such differences

always arise when the light is transferred from air to a Material, like it is if the light

cross a crack or from a material to another material.

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 13

Detect microholes with light!

The hole with a diameter of about 20 micrometers is reliably detected by the OCT

measuring principle. The viewing takes place from the bottom of the blister or from

the blister top. The microhole is located in the vertical side wall and is reliably

detected. We also distinguish a coloration from a continuous crack.

The microhole is clearly visible in the image stack of 500 images.

Vertical section through the whole stack

Micro hole in

the side wall

Top view on the

region of interest

Bottom of the blister.

(Inspection side)

Top of the blister

Micro hole in the side wall

Normal image

of the blister

Graphic to the situation

Micro hole in the

side wall

Direction of inspection

flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch


Seite 14

Laser marking for product identification

The labeling of products requires modern solutions to clearly identify them. With the

OCT process, the smallest shape structures can be safely and clearly inspected,

which increases process reliability and improves the efficiency of manufacturers and

processors.

C:\Visiotec\Detektion von Mikrolöchern.doc

Our systems have been developed for use in industrial monitoring and identification

processes. The ASP array captures one million times 90,000 pixels per second, that

means 90*10 9 Pixels per second.

Unlike conventional optical visualisation systems, OCT systems rely on

refractive index differences. This property makes the OCT systems not prone

to colors of a surface, it’s tilt and it's environment, or it's transparency.

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flo-ir Aawasserstrasse 10 Tel: +41 (0)41 871 39 88 info@flo-ir.ch

berührungslos messen CH – 6370 Oberdorf Fax: +41 (0)41 871 39 87 www.flo-ir.ch

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