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Why encoder and product detect signals are underrated aspects of printing applications

Updated: Oct 27, 2021

The encoder and product detect are like the conductor at an orchestra, they dictate the rhythm of the individual components of a print process and are therefore directly related to the print quality, reliability and speed.

Unsynchronised Jetting
Unsynchronised Jetting

As an inkjet technology supplier your relationship with encoders is a complicated one. Encoders and product detect are in most cases not part of your solution, but they have a great influence on its performance. Generally speaking, it is quite easy to define the kind of signal an encoder needs to deliver: One that tracks the exact movement of a substrate without slipping or skipping and is translated in a predefined type of impulse – easy as pie. But encoder and product detect can cause behaviours that are difficult to track back to their cause. It can sometimes feel like there is a ghost in the machine that is impossible to get rid of.

Encoder problems
Encoder problems

Encoder and product detect problems are most likely in disguise

When the encoder signal doesn't arrive at the exact same time, in the exact same quality at every point of a print system, the jettting can be too early, too late or even be skipped. This can cause unsynchronzied jetting of - individual colour rows - individual print heads - individual nozzle-lines of a print head

These problems can look very similar to a struggling ink supply, faulty electronics or a bad alignment of a colour row/the whole print system.

On the other hand, when encoder signals don't get lost, but instead are created at a very high frequency these clustered impulses can exceed the suitable frequency of a print head. The input of so many signals can cause a controller to crash or a fluid supply to collapse. The faulty ink supply then can suck in air and the result looks similar to an electronics problem or like a print fluid starvation. Often the encoder is not initially considered for these kind of issues.

Common causes for inaccurate encoder signals are EMC interferences. Mostly these are difficult to locate, since they only occur sporadically. For example, only when a certain machine is running at the same time, or only when the cabe inside the supply chain is in a certain position the problems are visible. The cause can also be long cables, heatings, motors...

This makes encoder problems even harder to track down or identify. Other reasons seem much more likely before the focus shifts to the encoder as the cause. But the sentiment at the end is always the same: “Why didn't I think of this earlier?”

Missing colours
Missing colours

With the product detect signal it is the exact same problem. Since it gives the impulse to start printing, the print can be started too early, too late or be skipped in case there is an error. This can happen only in individual colour rows or for the whole print system. The result can look very similar to electronic problems, issues with the ink supply, or a software error since certain colours or motives are just skipped/missing.

Analyse, filter and double-check

For a reliable print process it is therefore crucial to create and verify reliable and good quality encoder and product detect signals. This avoids chasing the intially mentioned ghost in the machine and waste time looking for problems where there aren't any. We strongly recommend adding these signals to the troubleshooting routine to identify or exclude them as possible reasons for undesired jetting behaviour.

To identify encoder problems faster and generate high quality signals – even in challenging production conditions – we developed a Signal Interface Box (SIB), that is connected between the encoder, the product detect and the print system. This way we are able to standardise the signals and get notified in case there is an error.

What is a Signal Interface Box?

The SIB is connected between the encoder, product detect and the print system. It builds the central hub and analyses, logs and – if neccessary – filteres and improves the encoder and product detect signals.

But not only the signals that go to the print system are analysed, the SIB builds a closed loop with the print system: It also analyses the signals after their return from the print system. This way the SIB can identify problems before entering the print system, but also problems that emerge when splitting up or processing the signal.

When two encoders are connected to one SIB it identifies slipping of the substrate, alignment and offset problems and compensates for variations in the conveying. The signals are compared to reference values and in case there are variations, a notification can be triggered or the signal can be filtered and improved automatically.

The SIB logs all data and has a small display for visualisation of the signals. Via a REST API the information about the product detect and encoder signal can be accessed, saved and visualised in the HMI of a printing line or printer.

By considering the encoder and product detect and developing a solution for faster troubleshooting and better quality signals, we got rid of a common issue in integration projects. With a standardised signal we have one less topic to worry about. With this article we want you to consider these aspects for your printers and integrations as well.

In case you find our solution helpful, we are happy to provide you more information on the Signal Interface Box.

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