什么是波形?
Last Updated on 4 月 24, 2025 by ImageXpert Team
An important part of an inkjet printing system is the waveform that is applied to the printhead, which is the driving force behind the drop ejection. The design of the waveform will directly impact the performance of the printer and print quality, but this waveform design is often not well understood. In this post we will discuss the fundamentals of the waveform – what waveforms are, how they work, and why they are a necessary part of your inkjet development. In the next post, you’ll find practical steps to go through the process of optimizing a waveform for your for your ink. Start with this article, and when you are ready to move on to editing your waveform, learn how to optimize one here.
WHY WAVEFORMS MATTER
The waveform is the electrical signal that is sent to each nozzle on the printhead that causes each individual drop to be fired. This electrical signal is sent to hundreds or thousands of individual nozzles simultaneously, thousands of times per second. The shape of the waveform signal will influence the size and speed of the drops. It also impacts the consistency of the jetting from one drop to the next, across the printhead, and over time. It also dictates the maximum speed that the printer can operate. The waveform holds a lot of power over the performance of the printer, especially for one setting tucked deep into the software that you might not even know exists.
If drop size, jetting consistency, drop placement accuracy, printing speed, or some other requirement of your application demands a high level of performance, optimizing every last detail including the waveform matters. If you are working with a challenging fluid, whether or not it comes out of the printhead or not at all will be dictated by your waveform design. With the right tools, making small waveform changes that bring huge performance improvements is a simple, quick process.
To showcase this, here is what one waveform setting change can do to the quality of your printing process. Both of these images are taken from the same printer, using the same ink, minutes apart. The only difference between them is a changing a single voltage setting in the waveform software.
High speed drops, lots of satellites. This is suitable for a large throw distance application that is very forgiving to satellites, such as printing on textiles.
Reduced speed drops, no satellites. This is suitable for a short throw distance application where satellites are problematic, such as printed electronics.
Using the wrong waveform for the wrong application will handicap your printing performance, leaving you to try to find formulation or mechanical solutions to overcome these setbacks. Waveform edits are much simpler, you just need to learn how to do it. Let’s get started!
THE BASIC PRINCIPLES OF AN INKJET WAVEFORM
To help understand how a waveform works, let’s take a look inside a nozzle chamber of a printhead. The image below depicts the jetting process known as fill-and-fire, which is common across many different printhead models. In this case, a stack of PZT (a piezoelectric ceramic material) deforms whenever voltage is applied to it, changing the volume of the ink chamber and causing the ink to move within it. If the ink moves enough, it will leave the nozzle as a drop. The means of applying this voltage to the PZT is the waveform.
In our example, the PZT is extended only when voltage is applied, so there will be no deformation until the printhead is plugged in. Once powered, the printhead maintains a specific voltage, causing the PZT to extend and remain in its non-jetting position (Left). If the voltage is decreased, the PZT retracts and creates an expansion in the chamber, drawing ink into it (Center). To eject a drop, the voltage is returned to its original value, the chamber shrinks, and the excess ink is forced out (Right). This process repeats thousands of times per second across every nozzle on the printhead.
The waveform is applied to the printhead through the electronics referred to as a printhead “controller” or “drive electronics”. These electronics send the signals and their software will have settings to control the shape of the signal. Here’s an example of a real waveform for a Dimatix printhead and Meteor drive electronics software for designing and applying it.
It is important to note that the actual shape of this pulse will vary with printhead design. Some printheads are driven by positive-going pulse, some by negative-going pulses, and some even go in both directions. Whichever way you’re used to looking at it, there are some fundamental settings that determine the shape of the waveform.
- The slope of the rising and falling parts (referred to as “slew rate”)
- The duration of the flat plateua (referred to as “hold time” or “pulse width”)
- The overall amplitude of the pulse (referred to as “amplitude” or “voltage”)
These come together to shape the pulse, which determines what is happening at the nozzle and ultimately how the jetting will perform. Let’s examine the timing in more detail.
脉冲计时基础
如果你在打印时站在打印头旁边,你可能会听到它“唱歌”,这取决于使用的频率。你能听到它的原因是因为致动器产生声波。对于喷射来说,最重要的是在墨水本身中产生的那些,因为它们定义了产生墨滴喷射的压力变化。
由于具有一定机械特性的墨水的存在,以及声波在反弹时会损失能量的事实,腔室内的压力可以被描述为阻尼谐振器。压力的任何变化,如压电陶瓷的变形,都会导致特征压力的变化。如这里所示,当压电陶瓷缩回并且腔室体积增加时,压力变化导致墨水开始在腔室内来回移动。
这种能量本身通常不足以使墨水喷出,它只是把墨水拉回到腔室的另一端,然后弹开。通过在正确的时间使用电压脉冲来增强压力,墨滴喷射变得更加有效,如下所示。当压力超过临界值时,由于优选的时机,墨滴喷出。
The reason the pulse timing is so critical is that if it is too short, or too long, then the waves, pressure, and movement of the PZT will be out of sync. If the ink is not moving the right direction at the time more pressure is added, instead of smoothly adding to the momentum, the momentum might be countered. It is similar to pushing a child on a swing. If you push them at the right time, the momentum is increased and they swing higher. If you push them at the wrong time, they will come to a violent stop. Similarly, if the pulse timing is wrong, the resulting jetting, repeated over and over, will be inefficient and unstable.
The image below shows the impact of pulse timing on the jetting. We’ve stitched together images of drops using different pulse duration. The time of capture of each slice is the same, so drops that are farther from the top of the image (the nozzle plate) are traveling faster.
As you can see, there is a clear pattern between how long the pulse is applied and the speed of the drop it produces.
Because the pulse duration is moving the fluid back and forth across the length of the nozzle chamber, and the length of the nozzle chamber is fixed for a given printhead, you might think that each printhead has a specific pulse duration to use. If you need a basic level of jetting performance, this can be true, and you can get a recommended general setting from the printhead OEM. However, the timing is also impacted by the speed of sound for that particular fluid. When you require high levels of jetting performance, the waveform must be tuned for a particular ink and printhead combination.
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什么是共振?
通常,在一个频率下工作良好的波形在另一个频率下可能工作不佳。这一切都归结于墨水在腔室内来回移动时的脉冲定时。随着印刷频率的增加,由给定脉冲产生的波和运动可以开始与前一个脉冲相互作用。在某些频率下,这将是加强,结果是共振,如在图像的顶部例子。
印刷频率越高,当下一个压降和压力波出现时,压力还没有衰减到零的可能性就越大,因此燃烧不佳的可能性就越大。如果墨水仍在流动,先前的脉冲可能会增加压力(更高的速度、更多的卫星、润湿)或降低压力(更低的速度)。如果您的打印速度灵活,明智的做法是在一定的频率范围内研究墨滴的形成,以确保您的最终打印速度不会落在发生共振的频率范围内。
Here’s a real life example of resonance at work. As you can see, the jetting quality is significantly worse at a specific range of frequencies (19-23kHz). The drop velocity is higher, there are more satellites, and the performance is unstable. But at frequencies higher or lower than this range, the performance normalizes. Understanding this phenomenon allows you to set your printer to ensure it doesn’t operate at these speeds, or tune the waveform to minimize the effect.
WHAT IS CROSSTALK?
Crosstalk is a broad industry term for unintended interference between printheads, nozzles, and droplets when printing. Two systems that perform well in isolation might start to show image quality issues when combined together. Crosstalk can be aerodynamic, mechanical, fluidic, or electrical.
We’ve learned that waveforms are thousands of individual signals sent to nozzles, thousands of times per second. Nozzles are packed together closely in the printhead. In a production printer, there are probably dozens or more inkjet printheads nested closely together. Surrounded by motion stages, ink supplies, dryers, UV lamps, and all sorts of other electronics. That is a lot of precision electrical signals happening in a tight space. Understanding your desired waveform shape and expected drop performance will help diagnose any potential electrical interference that happens in a production machine.
Inside the printhead itself, it is possible for one nozzle firing to influence the behavior of the nozzles around it. You might find that the drop volume from a nozzle is slightly higher or lower if the adjacent nozzles happen to be jetting at the same time. A well optimized waveform with that limits excess electrical or mechnical energy can help minimize this.
多重脉冲
If the electronics allow it, the waveform doesn’t have to be limited to a single pulse. Multiple pulses can be used at each pixel, which can bring a variety of benefits.
Stringing multiple pulses together allow you to create larger, faster drops than one fill-fire cycle can do alone. Waveforms for multi-pulsing usually rely on the first or second resonance in the pressure wave. This means that the first pulse will add to the pressure of the ink when it is moving towards the nozzle. Some of the ink will eject and the rest bounces off the orifice and returns to the opposite wall. Once the ink is moving towards the nozzle again, a second pulse will add to its momentum. The pulses should be tuned carefully; the reinforcement can be very strong, overdriving the pressure and creating nozzle wetting.
Having the ability to see the drop formation in real time is helpful in understanding these effects. In the photos below, taken with the JetXpert Dropwatcher, you can see drops of different sizes being formed in adjacent nozzles by a resonant multi-pulse waveform. The nozzle to the left had three pulses of a waveform applied to it, the center nozzle only had the last two pulses, and the right nozzle only had the last pulse. The three pulses used to create the drops were evenly-spaced in time, and each image was taken at the time where the pressure wave hit the opening of the nozzle.
请注意脉冲结束后喷嘴弯液面的延伸,这是由压力波引起的。第一种甚至发生在韧带分离之前。发射了两次或更多次的喷嘴上的弯月面凸起更大,这证实由于先前的脉冲已经施加了额外的压力。通过调整脉冲时间和可视化您的进度,您可以更快地改善特定油墨的波形。
The extra pulses aren’t only used for jetting larger drops. It is common to use a pre-pulse on the “off” data to tickle the nozzles, meaning that enough force is provided to keep the ink moving within the nozzle, but not eject a drop. Keeping the ink moving in the nozzle helps slow down drying or particle settling. We discuss this topic in more detail in our article on this Latency effect.
You can also use additional pulses to dampen this accoustic momentum. A well-timed, low voltage pulse that works against the pressure wave in the nozzle will bring the nozzle to a rest state faster. This is particularly useful at high frequencies to cancel the previous drop to avoid resonance.
The waveform below has many such features built in and is adapted from a Ricoh patent for a desktop printer.
MAIN TAKEAWAYS
These electrical waveform signals play a big role in the overall performance of the printer by influencing drop size, speed, and stability. For applications that push the limit of inkjet technology, the shape of the waveform needs to be finely tuned for your particular fluid and drop requirements. With the right tools and knowledge, basic modifications to the waveform can be made quickly, which will have a high impact on performance. Ready to get started? Let’s continue on to learn the step-by-step process of how to optimize a waveform for a particular ink.