Creo's FM site - Staccato
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FM screen printing has always been the most perfect way to add screen images to all printers. It not only solves many problems such as collision net, moiré, and moiré in multi-color printing, but also greatly improves the detail and level of image performance. Almost all prepress printing equipment manufacturers have their own FM screening technology, such as Heidelberg's diamond network, Agfa's crystal net and so on. Of course, they also printed a lot of printing samples of the FM network, everything looks perfect. But... Ten years have passed, it seems that all of this has only stayed in the lab, and almost no one has actually applied this screening technique to actual jobs during printing.
why?
Because the CTF's workflow is too long, it is sometimes too difficult to perform rigorous process control on each of these steps. The emergence of CTP has solved the problem of the process to some extent. But even if it is directly imaged on the PS version, the instability of the dot expansion of small dots is still a serious problem. The solution to this problem is: "square laser point technology." Creo has conducted long-term and in-depth research on FM sites. From a technical point of view, we believe that square laser point and quadratic FM screening technology are necessary factors to achieve a truly practical FM network. Both are indispensable.
●Square laser point technology
The Creo square laser spot, which has won many new technology awards internationally, is not simply a square shape of the laser spot. Conventional CTP lasers are a laser tube that emits a spot for actual exposure, so the imaging point inevitably inherits the Gaussian energy curve of a single laser tube. Creo's square laser spot is cut by Creo's patented "light valve." The energy curve is nearly straight and can form extremely sharp spots on the plate. Don't worry about the impact of changes in the back-end printing conditions on the dot size. Compare the data in the left picture:
Imagine that if the edge of the dot is only 1 μm in size, the unpredictable change of the 200 lpi conventional screened dot is less than 3%, but the uncontrollable change of the 10 μm FM dot reaches 30%. If a print has 30% dot expansion that cannot be adjusted, it means that the finished product we print is completely non-repeatable, let alone any quality control.
Through the "light valve", Creo is one of the companies that can precisely control the laser edge to ±0.2μm (even if the back-end plate condition changes by 10%), we can control the expansion rate of the 10μm FM network to within 4%.
●Secondary frequency modulation screening technology
Why is FM screening still divided twice?
Once the FM network is just using a random algorithm, the original network points in the unit area are fully broken up, so there is a high probability of duplication in the middle adjustment (50% of the flat net). When the midtones of multiple color plates are superimposed on each other, stripes like water waves are generated. That is what we call low harmonics. In response to this phenomenon, we will first reorganize the FM network that has been completely dispersed, and then break it up again to get the required secondary FM network.
The usual FM network screening network expansion is relatively large. This is because the dot expansion only occurs at the edge of the dot, and many small dots after the original large AM site are scattered, the sum of the perimeters of the dots is much larger than the original large dot. The secondary FM screening connects the adjacent small dots when reorganizing the dots, which greatly reduces the total perimeter of the dots, making the dot expansion easy to control.
● The specific implementation of FM network printing.
1. The printing density and dot expansion that is satisfactory to customers is the first step.
The printing consumables used in printing factories in mainland China are more complicated, and the process control for the printing process is relatively poor. Let us first look at the branch expansion shift in the ideal environment (see Figure 1).
The actual situation (see Figure 2) is that the control of the film is relatively simple, and the density and linearity can be easily controlled using a transmission density meter. This part of the printing process is rather confusing, and usually 2% of the outlets can still be retained as a standard. Due to the lack of reliable detection equipment, the loss of the dots is actually too large (usually around 10%), which eventually leads to loss of control during printing.
Therefore, it is an effective means to make the customer clear the target by first using the amplitude modulation dot to print a print with a controllable constant dot expansion rate. Usually Chinese customers do not want printing outlets to expand like European standards, but prefer brighter and lighter works, so Japan's printing characteristics are sometimes better, and of course, it is necessary to make customer-specific adjustments based on different inks and papers.
2. Measuring the expansion rate of the printing dot of the FM network.
The dot spread curve of the Staccato secondary FM site is quite different from that of the conventional AM network (see Figure 3). Since the dot expansion can only occur at the edge of the dot, the maximum dot gain of the AM network always occurs at 50% (the longest dot edge at that time). Looking at Staccato again, you will find that the total perimeter of the 75% dot is longer than 50%, so its dot expansion curve is also very special. Such a dot expansion curve is also very special. Such a dot expansion curve brings great advantages to the actual printing, because the dot expansion usually becomes larger as the ink density increases, and the maximum change of the amplitude modulation network occurs in the middle adjustment, so the human eye can easily see the difference. (People are most sensitive to middle notes). However, for Staccato, as the density of the ink increases, the dark tone changes first and the midtone changes are not obvious. Therefore, the FM dot printing is easy to ensure the consistency of the printing tone.
3. By adjusting the linear curve of Staccato, the FM network is used to simulate the customer's approved dot expansion rate.
We have the actual measured curve and also have a target curve. All we have to do is to use Staccato to simulate the output of the AM network (see Figure 4). All of this is much easier than you think.
There are currently two actual users in mainland China who are using the Staccato secondary FM site for printing. We hope that China's printing quality can be pushed to a new peak through extensive practical use of FM printing!