How to Teach a Flow Wrapper Print Registration Photocell

A Step-by-Step Guide for GSP, Tecno Pack & Similar Flow Wrappers

Printed film registration is one of the most important functions on a horizontal flow wrapper. If the photocell is not taught correctly, the machine may:

• cut through the artwork,

• produce inconsistent bag lengths,

• drift out of registration,

• or fail to detect the print marks altogether.

In this guide, we’ll explain how a print registration photocell works, why correct teaching is important, and how to teach the sensor in a few simple steps.

This example uses the Wenglor WM03PCT2 print mark reader commonly fitted to GSP and Tecno Pack flow wrappers. However, similar teaching procedures are also used on many other machines including certain PFM, ULMA, and other horizontal flow wrappers, while some systems may instead be fitted with Omron or SICK print registration sensors.

What Does a Print Registration Photocell Do?

A print registration photocell detects the eyemark printed on packaging film.

The machine uses this eyemark to synchronise the sealing jaws and cutting position with the printed artwork on the film.

Without a photocell, the machine would simply run on fixed bag length. This is suitable for plain film, but printed packaging requires the machine to constantly track the print position to ensure the artwork stays aligned correctly.

The photocell continuously scans the film as it moves through the machine. Every time the sensor detects the eyemark, the machine updates the cut position accordingly.

This ensures:

• consistent bag lengths,

• centred artwork,

• correctly positioned logos,

• and accurate cutting between products.

  
  

The Sensor Used on Our Machines

At PacMatix, we commonly use the Wenglor WM03PCT2 print mark reader on GSP and Tecno Pack flow wrappers because it is simple to teach and performs reliably across a wide range of packaging films.

In real production environments, operators often need to run:

• different eyemark colours,

• varying film background colours,

• metallic films,

• reflective packaging materials,

• and multiple product changeovers.

Some lower-end print registration systems can struggle with reflective or inconsistent film surfaces, leading to unstable registration, drifting cuts, or unreliable detection.

The Wenglor sensor allows operators to quickly teach the sensor using the actual print mark and background colour being used on the film. This makes it highly flexible for modern packaging environments where multiple film designs and materials may be used throughout the day.

These sensors are also widely used across many European flow wrapper brands due to their reliability and ease of setup.

Wenglor WM03PCT2 print registration photocell commonly used on GSP and Tecno Pack flow wrappers for detecting eye-marks on printed film.

When Does a Photocell Need to Be Re-Taught?

The sensor should generally be re-taught whenever:

• changing to a different printed film,

• changing film supplier,

• changing artwork colour,

• switching to metallic or reflective film,

• replacing the photocell,

• or when registration becomes unstable.

Even small changes in colour contrast can affect how the sensor detects the eyemark.

Correct teaching helps ensure reliable operation and reduces wasted film and product.

Step-by-Step: How to Teach the Photocell

Step 1 :

Position Photocell Correctly

Move the photocell along the guide, bringing the reading radius flush with the edge of the film, then lock the photocell in position using the adjustment knob.

Step 2 :

Position Eyemark Under Photocell

Draw the film by hand until the printed eyemark is positioned directly under the photocell beam.

Step 3 :

Teach the Eyemark

Press and hold the rear teach button until the yellow light on the side of the photocell begins flashing, then release the button.

Step 4 :

Position Background under Photocell

Pull the film forward until the printed eyemark moves outside the photocell sensing area.

At this stage, the photocell should only see the background colour of the film.

Step 5 :

Confirm the Teaching Procedure

Press the rear teach button once more briefly.

The yellow indicator light should flash once to confirm that the photocell has successfully learned both the eyemark and the film background.

Step 6 :

Verify Eyemark Detection

Slowly pull the film through the photocell and confirm that the yellow indicator light switches each time the printed eyemark passes through the sensing area.

This confirms that the photocell is correctly detecting the print registration mark.

Common Problems After Teaching

Even after teaching the photocell, registration problems can still occur.

Sensor Does Not Detect the Eyemark

Possible causes include:

• sensor too far from film,

• reflective glare,

• damaged print,

• incorrect teaching process,

• or a dirty sensor lens.

Sensor Flashes Randomly

Possible causes include:

• reflective film surfaces,

• excessive ambient light,

• incorrect sensitivity,

• or contamination on the sensor lens.

Machine Cutting Through Artwork

Possible causes include:

• unstable film tension,

• incorrect bag length settings,

• poor photocell positioning,

• weak eyemark contrast,

• or slipping film feed belts.

Registration Drifts During Production

Possible causes include:

• inconsistent film tension,

• moving film reel,

• unstable product spacing,

• worn or poorly adjusted fin sealing wheels,

• or poor-quality film printing.

Fixed Length vs Print Registration

Flow wrappers generally operate in two different modes.

Fixed Length Mode

The machine cuts at a fixed bag length regardless of printed artwork.

This is commonly used for:

• plain film,

• unprinted packaging,

• or simple products.

  
  

Print Registration Mode

The machine uses the photocell to track the eyemark and continuously correct the cut position.

This is essential when running:

• branded film,

• centred graphics,

• barcodes,

• logos,

• or printed nutritional information.

Without proper registration, the artwork position can drift and the packaging appearance becomes inconsistent.

Why Proper Teaching Matters

Correct photocell teaching is a small setup procedure that can have a major impact on packaging quality.

A properly taught sensor helps:

• reduce wasted film,

• minimise rejected packs,

• improve packaging appearance,

• reduce downtime,

• and improve operator confidence.

In modern production environments where multiple products and films are run throughout the day, understanding how to correctly teach the photocell is an important operator skill.

Final Thoughts

Teaching a flow wrapper print registration photocell is actually quite simple once the process is understood.

The key is ensuring the sensor clearly learns both:

• the eyemark itself,

• and the surrounding film background.

With a reliable sensor and correct setup procedure, modern flow wrappers can run printed film accurately and consistently across a wide range of packaging materials.

If you need assistance with flow wrapper setup, troubleshooting, training or service support, feel free to contact the PacMatix technical team.

Frequently Asked Questions – Flow Wrapper Print Registration & Photocell Setup

1. What does a print registration photocell do on a flow wrapper?

A print registration photocell detects the eyemark printed on packaging film so the flow wrapper knows exactly where to seal and cut each pack. This ensures logos, graphics, and text remain correctly positioned on every package.

Without proper print registration, packs can drift out of alignment, causing poor presentation, wasted film, and inconsistent bag lengths.

2. Why is my flow wrapper cutting in the wrong position?

Incorrect cut position is commonly caused by:

• Incorrect photocell teaching

• Dirty or damaged photocell lens

• Weak print contrast on film

• Film tracking problems

• Unstable film tension

• Worn film brake systems

• Worn or slipping fin wheels

• Poorly adjusted fin seal wheels

In many cases, operators immediately blame the photocell itself, when the real cause is mechanical instability somewhere in the film transport system.

Worn fin wheels or incorrectly adjusted fin seal pressure can cause the film to slip or feed inconsistently through the machine. When this happens, the print registration position drifts relative to the sealing jaws, resulting in incorrect cut positions and unstable registration during production.

3. How do you correctly teach a print registration photocell?

The exact procedure varies between manufacturers, but the basic process usually involves:

1. Positioning the photocell correctly over the eyemark

2. Teaching the “light” background colour

3. Teaching the darker print mark

4. Verifying stable signal switching

5. Running the machine slowly to confirm consistent registration

It is important that the photocell sees a strong contrast difference between the print mark and the surrounding film.

4. Where should the photocell be positioned on the film?

The photocell should normally be positioned so the sensing spot reads the edge of the eyemark rather than the middle of the mark itself.

This creates a cleaner transition between light and dark areas, helping the sensor switch more consistently at high speed.

Poor positioning can cause unstable readings and inconsistent registration.

5. Why does the photocell work sometimes but lose registration during production?

Intermittent registration problems are often caused by mechanical movement in the film rather than an electronic fault.

Common causes include:

• Unstable film tension

• Worn brake assemblies

• Film wandering sideways

• Loose rollers

• Damaged bearings

• Inconsistent film unwind resistance

• Slipping fin wheels

• Incorrect fin wheel pressure settings

If the film physically moves during operation, the photocell may no longer see the eyemark consistently.

6. Can bad film tension affect print registration?

Yes — film tension is one of the biggest causes of print registration instability.

If the film tension changes during operation, the eyemark position shifts relative to the sealing jaws, causing the machine to chase the print and lose synchronisation.

Modern flow wrappers often use dancer systems or motorised film unwind control to maintain stable tension throughout production.

7. Why is my photocell signal unstable?

An unstable signal can be caused by:

• Poor colour contrast on film

• Reflective packaging material

• Dirty photocell lens

• Incorrect sensitivity settings

• Incorrect sensor angle

• Film movement or vibration

• Worn mechanical components

• Film slippage through the fin wheels

Before replacing the photocell, always inspect the mechanical film path carefully.

8. Can worn fin wheels affect print registration?

Absolutely.

The fin wheels play a major role in pulling and stabilising the film through the flow wrapper. If the wheels become worn, glazed, contaminated, or incorrectly adjusted, the film can slip during operation.

This causes inconsistent film movement, unstable bag lengths, and print registration drift.

In many situations, photocell problems are actually symptoms of poor film transport through the fin wheel section.

9. Can a damaged or worn film brake system cause drift?

Yes.

Older flow wrappers often use mechanical brake systems on the film reel holder. If these systems become worn or inconsistent, film tension fluctuates continuously during operation.

This causes the film to wander and the eyemark position to drift, resulting in unstable print registration.

10. Why does print registration work at slow speed but fail at high speed?

At higher speeds:

• Film tension changes become more aggressive

• Film vibration increases

• Poor sensor positioning becomes more noticeable

• Weak contrast becomes harder for the sensor to detect consistently

• Film slippage becomes more apparent

• Worn fin wheels may lose traction under load

A setup that appears stable during slow jogging may become unstable once the machine reaches full production speed.

11. Do all flow wrappers use the same photocell teaching method?

No.

Different manufacturers use different teaching procedures and different photocell technologies. Some systems use automatic teach modes, while others require manual threshold adjustment.

However, the fundamental principle remains the same:the sensor must clearly distinguish between the print mark and the background film.

12. Can PacMatix help diagnose print registration problems?

Yes.

PacMatix Pty Ltd regularly assists Australian food manufacturers with flow wrapper troubleshooting, print registration issues, photocell setup, film tracking problems, and preventative maintenance across a wide range of flow wrapper brands.

We also supply and support Italian-built horizontal flow wrappers from GSP Packaging Machinery and Tecno Pack S.p.A..

About the Author

Ettienne van Vuuren is the Director – Technical & Sales at PacMatix Pty Ltd and has worked with horizontal flow wrappers for over 25 years.

His experience includes machine commissioning, troubleshooting, operator training, and print registration optimisation across bakery, snack food, fresh produce, dairy, confectionery, and pet food packaging applications throughout Australia.

Before founding PacMatix, Ettienne worked extensively on horizontal flow wrapper systems and film transport diagnostics.

Today, PacMatix supplies and supports flow wrapping systems across Australia, including GSP and Tecno Pack equipment, while also assisting customers with troubleshooting, servicing, and production optimisation.

Continue Learning

👉Explore more technical troubleshooting articles in our KWIK TECH GEMS™ resource centre.

👉Explore more flow wrapper training articles and videos articles in our Flow wrapper Training resource centre.

👉 Need help with print registration or photocell setup? Contact the PacMatix technical team for support across Australia.

Published: May 2026