Kyle Pucci, 5月 11, 2018

在我们关于喷墨波形的介绍性文章中,我们描述了什么是波形,以及如何将其应用于打印头的过程。现在我们考虑如何使用适用于许多打印头的通用 墨滴观测方法来优化该波形以获得更好的喷射效果。在本文中,我们将逐步地使用Dimatix Samba打印头来提供示例图像和数据。 introductory article on inkjet waveforms, we described what a waveform is and how the process of applying it to the printhead works. Now we consider how to optimize that waveform to get better jetting, using a general dropwatcher approach that applies to many printheads. For those of you that have received a waveform from your printhead or ink supplier, you may be wondering whether waveform optimization is necessary and worth your time and effort. In some cases, a generic waveform that is not tuned for a particular ink or industry application is good enough, but in many cases it is not.

To help explain, rather than printing images, let’s consider the process of taking images. On your digital camera there are settings for white balance, exposure, shutter speed, etc to help control how the image is captured. The camera comes with a preset combination of settings that will work well for general use, and this is probably what most people use – just point and click. But when you want to shoot images at night, or on a sunny day, or of a person, or of a landscape, a professional photographer is able to manipulate the settings to get much better results for each of these very different scenarios. Inkjet waveforms are very similar – there is such a difference in requirements between printing a coating, a graphic, a circuit board, or a metal part that a generic combination of waveform settings won’t be able to perform well in all of them. Nobody knows your ink and application like you do, so we want to bring you up to professional status with the knowledge to tune a generic waveform to get optimal results for your exact application.

In this article, we will follow along step-by-step with a Dimatix Samba G3L printhead to give example images and data along the way.




The first step of any attempt to develop a waveform is to clearly define the goal. Usually, the most important targets to identify are the desired drop size, drop velocity, and jetting frequency. If you already know the target specifications, then you can get started straight away. If not, then you will have to do some investigation. Remember that different applications will have very different requirements for the jetting performance. Coating applications are primarily concerned with maximum throughput, and the stability at different speeds or number of satellites are of little concern. Contrast this to printed electronics, where printing consistency is everything. The printheads are very close to the surface, so slow drop velocities are acceptable, but no satellites and consistency in drop size across the printhead are crucial. Direct to shape applications have varying distances to the surface, so the drop speed and therefore throw distance should be maximized. 3D printing applications don’t want speeds that are too high (cause powder splash) or too low (won’t penetrate the powder). As you can see, you have to understand the needs of the application before beginning the process of tailoring a waveform to it.

If you are an ink company and have a specific machine to develop for, check with your customer what the usage conditions of the ink are. If your customer is an equipment manufacturer, they should be able to tell you all you need to know. If selling direct to user, then perhaps this information is not so easily available and you’ll have to work a bit harder to figure out what’s sensible.

One question that we are commonly asked is how to determine the necessary jetting frequency for your application. This is directly related to the printing resolution (in the process direction) and the carriage speed. In a simple example, let’s say you have one printhead printing at 600dpi and are printing in one pass at 100 inches per second. 600 dots per inch multiplied by 100 inches per second equals 60,000 dots per second – your jetting frequency! This equation gets a little more complicated when you print multiple passes or have multiple printheads. For example, if it took you two passes instead of one to print 600dpi, that means each pass is only 300dpi. Recalculating our frequency brings us to 30,000 dots per second. Instead of a single printhead, you had two printheads working together, that means each pass is really only 150dpi per head. Recalculating our frequency brings us to 15,000 dots per second for each head. With this basic knowledge, you can calculate how fast each printhead will be jetting on more and more complex machines to determine which frequency you should be optimizing your waveform for.


波形优化的第一步是为我们的喷射建立一个合理的基线,以便我们用dropwatcher进行查看。如果可能的话,一个简单的方法是从打印头制造商推荐的或默认的单脉冲波形开始。除了典型的脉冲定时,通常还会有某种校准电压(有时称为“标签”电压)。使用这个开始是因为它应该产生合理的喷射。对于我们的Dimatix Samba示例,我们将从打印头用户手册中的波形开始:脉冲宽度2.18us、振幅脉冲26V(包括40V/us上升时间)。

下一步是让墨滴在观墨仪器的视野中可见。如果可能的话,你能看到喷头面板是很重要的;如果你失败了,这些也对找到失败的原因有很大帮助。下图给出了Dimatix Samba打印头的理想视图。







对于我们的Samba打印头,我们将自动以0.1微秒的增量扫描从1.1微秒到3.3微秒的脉冲宽度。通过在每个值(使用双脉冲)捕获图像,我们能够快速判断下落的速度,并在需要时补充测量值。下图是使用XSweep和Stitch的组合生成的。 XSweep and 缝线.


根据我们的图像,可以看到2.1-2.2微秒的脉冲宽度似乎产生了最高的液滴速度。我们可以分辨,因为图像的每一片都是在同一时刻拍摄的,并且墨滴在这些片中离打印头最远。如果你还记得,2.18us是我们在Dimatix Samba手册中的起始脉冲宽度,事实上它似乎是最佳的。干得好Dimatix !


就像喷墨打印中的大多数设置一样,用户可以自行决定处理过程的精确度。在波形优化的情况下,选择较小的间隔来测试每个参数将能够给你更精确的结果。然而,当手动进行这种分析时,较小的间隔意味着进行这种测试所需的时间增加。为了加快进程,ImageXpert有一个名为XSweep的工具,它会自动调整波形设置并为您执行测量。 XSweep, which will automatically adjust the waveform settings and perform the measurements for you.



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正如我们之前确定脉冲宽度 的方法一样,让我们尝试一系列电压,并测量每个电压下的液滴速度。关注墨滴体积和卫星形成也很重要,因为这会影响我们的决策。在这一点上,目标是确定电压设置,在没有太多卫星的情况下,为我们提供目标体积和速度。借助Samba,我们将自动以0.5V的增量扫描21V-31V的电压。输出如下所示。





Now that you’ve improved your pulse and it’s producing the velocity you’ve been looking for, it is time to push the head a bit harder and turn up the frequency. This will test whether the waveform we’ve built so far performs well at our target frequency, as well as if there are any particular spots to avoid. If you already know what your key target frequency is, then you can save some time by just looking at jetting there, but don’t forget to include the subharmonics too. You may be surprised to learn that when an image is rendered and printed, the print resolution is not necessarily constant across the whole image. To help improve the appearance of the image, the resolution is increased for darker portions and decreased for lighter portions, making it possible to print a gradient even if you only have one available drop size. The resolution is commonly divided in half or in thirds, so testing one half and one third of your target frequency will ensure your waveform will still perform well after rendering.

我们认为通常最好尽可能了解整个频率空间。您已经设置好了系统,并且您永远不知道客户何时会要求以另一种频率使用该墨水。除了XSweep之外,Imagexpert还提供频率扫描附加组件,以帮助加快过程。这将自动扫描一系列频率并收集数据,这对于较高频率的打印头尤其有用。下图是我们以1千赫的步长以1–30千赫喷射的Samba波形。 Frequency Sweep Add-On to help speed up the process. This will automatically sweep through a range of frequencies and collect the data, which is especially helpful for higher frequency printheads. The image below is our Samba waveform jetting at 1 – 30kHz in 1 kHz steps.








让我们复制之前创建的优化脉冲,并调整这两个脉冲之间的间距,分析每一步的喷射。 一个好的起点是改变间隔,从最小允许值到每个脉冲宽度的两倍。 最好的测量方法是观察第二个流出的液滴的速度(如果有的话),因为这个液滴的速度对第一个脉冲引起的压力波动非常敏感。 在一些头/墨水组合的低脉冲间隙中,液滴很可能在你有机会测量它们之前就已经合并了,而在其他情况下,第二次喷射可能会出现在第一次韧带上的凸起。 重要的是找出在什么间隔下你可以测量到的下降速度最快。大多数成功的灰度波形都是在共振周期或共振周期附近工作的,因此在给定输入量的情况下,喷射是最优化的。






The reason we chose 5-pulse for 3 levels because it demonstrates nicely the high degree of flexibility that is possible, including the fact that pulse do not have to be identical or be linear in amplitude (like our first examples). The one thing to keep in mind is that the maximum frequency that can be used will be the inverse of the time taken to complete the whole waveform, regardless of which grey level you are selecting. For example, let’s say that you have three pulses in a waveform, each with a duration of 10us. Even if Gray Level 1 only uses a single 10us pulse, the maximum frequency that you can print at Gray Level 1 is based on 30us timing.




The multi-pulsing approach can also be useful for controlling nozzle plate wetting, or influencing ligament break-off, for example. Extra pulses can come before or after the main ejection pulse as shown below. Tips for implementing more advanced waveform tricks are hard to systematize but we wanted to make sure you know these things are possible. Two common types of pulses are pre-pulses and dampening / cancel pulses.

Pre-pulses are low amplitude pulses that come shortly before the main pulse, designed to help improve the efficiency of the ejection of the drop. They can help get the ink moving so that the ejection pulse has less energy to overcome (like rocking something before tipping it over). The timing of these pulses is critical to ensure that they are working with your main pulse and not against it!

Dampening pulses are a similar concept but appear at the end of the waveform. After a pulse, there is some residual energy within the ink and it will continue moving inside the nozzle until it fades away. This can cause trouble at high frequencies, because the next cycle is starting while there is still movement in the nozzle, potentially leading to harmonic behavior. A perfectly-timed dampening pulse will work against the residual motion of the ink in the nozzle, bringing it to a stop. Reducing the oscillations of the ink in the nozzle may also have other benefits such as reducing wetting or shorter ligament length.

Slew rate is another term that you may have encountered in your waveform studies. The piezoelectric material that the nozzle walls are made from can only react so quickly, so there is a limit to the amount of voltage that you can apply to them in short intervals. The slew rate is the change in voltage over the change in time, almost like the acceleration of the walls. Printheads call for the sloping edges of the waveforms to fall within a certain range of slew rates for safe operation. Manipulating the slew rate may have some impact on the waveform and can be explored, but it is not nearly as noticeable as pulse width or voltage.