Product speed and length

From speed to product length

The optical velocimeter measures the instantaneous speed of the material and, by integrating it over time, derives the length with high resolution. This data directly governs the cutting position and the piece count. Since the measurement is made without contact, there is no slippage: the length error is permanently reduced, to the benefit of product quality and material yield. As a result, scrap and disputes with customers decrease.

For fast lines the VLM500 is used (up to 50 m/s, uncertainty < 0.025 %); for the direct replacement of measuring wheels and for low speeds the VLM60 is ideal, accurate even at 0 m/s.

Piece counting and cut-to-length

In lines that produce bags, labels, sheets or cut lengths, piece counting and cutting length must be accurate and repeatable. An optical measurement with a fast update time makes it possible to trigger the cutter at the exact instant, keeping the length constant even when the line speed varies. For example, in label production, the accuracy of the length determines the correct die-cutting position.

Advantages for web products

• Accurate metre counting and length for rolls and products
• Accurate cut-to-length on bags, labels and sheets
• Non-contact measurement: no marks on the products
• Stable tolerance over time, without frequent recalibrations
• Integration with existing cutters, rewinders and counters

Registration and synchronisation

A stable speed measurement contributes to registration in printing presses and to the synchronisation of the units in converting lines. Keeping the ratios between the different stages constant reduces material waste and improves product quality. In addition, the availability of the data in real time facilitates automatic line adjustment, reducing manual intervention by the operator.

Since the signal is digital and drift-free, integration with supervision and labelling systems is simple and direct.

Reliability and return on investment

The absence of contacting parts eliminates the wear and periodic maintenance typical of measuring wheels. As a result, the line runs with greater continuity and the measurement maintains the same accuracy over time. Ultimately, especially in high-volume production, the return on investment is rapid: less scrap, fewer stoppages and more consistent product quality. RODER technical support assists the customer in choosing the model and during installation.

Recommended products

Use cases in converting and printing

Speed and length measurement of products is used in many processes: rewinding with rolls cut to nominal length, production of bags and carrier bags to size, printing and die-cutting of labels, sheet cutting and lamination of laminates. In each case the same quantity, measured without contact, governs cutting and counting, ensuring the dimensional consistency of the finished product and the correct numbering of the pieces.

For example, in the production of self-adhesive labels, the accuracy of the length determines the die-cutting position and the number of labels per roll; an error of a few millimetres, repeated over thousands of pieces, results in scrap and disputes. Optical measurement eliminates this source of error at the root.

Length data and traceability

In addition to governing the cut, the length data feeds production documentation and traceability. Knowing exactly how many metres have been produced on each roll facilitates order management, automatic labelling and reporting to the customer. Since the signal is stable and drift-free, integration with management and MES systems is simple, with no need for the compensation for wear typical of contact measurements.

Managing format changes

Lines that produce bags, labels or sheets face frequent format changes. With a measuring wheel, each change may require checks and recalibrations; with optical measurement, on the other hand, switching from one format to another does not affect accuracy, because the measured quantity is the same regardless of the product. As a result, set-up times are reduced and the line quickly returns to full speed, an important advantage for small-batch production.

Accuracy and repeatability over time

The difference between a good and a bad length measurement is not seen on a single piece, but on the thousands of pieces in an order. A small systematic error, multiplied, becomes significant scrap. Optical measurement, free from slippage and wear, maintains a stable tolerance throughout production, without drift. For this reason it guarantees consistent quality even on long runs.

Data shared with several systems

The speed and length signal can be distributed simultaneously to several recipients: the cutter control, the line counter and the management system. Thanks to the encoder, analogue and fieldbus outputs, the same data feeds both the control functions and the production documentation, avoiding duplicated sensors and simplifying the line architecture.

Frequently asked questions

Related products

The RODER instruments for this application. Go to the relevant catalogue pages for models, technical data and documentation.