How does an inkjet printer work?

An inkjet printer is a process of creating a digital image by spraying ink onto paper. Many devices such as a scanner, photocopier, and fax machine are along with the printer in a single box. In this article, I will mainly explain the engineering behind the droplets and how the colour algorithm creates the final image. An Inkjet printer technology is truly the magic of C(Cyan), M(Magenta), and Y(Yellow) colours which I will elaborate in the next article.

Role of nozzle in printer

In every printer, printing is possible because of tiny dots of ink. A Nozzle is a small hole found on a printer cartridge. You can print any image with a collection of many dots. Each nozzle produces millions of ink droplets. As you can see in fig 1, these dots are produced by drops of ink being released from many nozzles. The ink is not dropped continuously but in a discrete and controlled way. The small circumference of the nozzle and backpressure inside it won't allow the ink to leak out, allowing for a precise image.

Fig 1 : Nozzle releasing ink drops

Role of heating resistor

To release the ink, I must use these small heating resistors(refer fig 2). These resistors are so responsive. Can you imagine how fast resistors heat? The resistors can gain around 100 degrees Celsius per microsecond. To release a drop of ink, simply supply the power to the respective resistor.

Fig 2 : Heating resistor

How does drop formation happen in a printer?

A resistor will heat up and vaporise the ink, thus forming a bubble(refer fig 3a). This bubble acts as a piston to push the ink out of the nozzle. However, when the primary drop is falling, the ink gets elongated due to viscosity. As a result, it forms one more drop (refer fig 3b), which falls near the primary drop. After some time, both drops combine into a single drop. Focus on the top region in fig 3b. Here, after some time, the heater is turned off, causing the vapour around the coil to condense and the bubble to collapse.

Fig 3a : Vapour bubble is create due to heating resistor
Fig 3b : Resistor turned off and drop released

The backpressure of the ink sucks outside air into the nozzle. Immediately afterwards, the surface tension of the meniscus will play an important role by working against the backpressure, forcing the fresh ink to fill the nozzle and remove the air from it (refer fig 3c).

Fig 3c : Fresh ink flows in the nozzle

What components are involved in the printing process?

Let's see what is inside the components of the printer. An ink tank is connected to the print head via a connection pipe you can see in (refer fig 4a), which is free to move along this horizontal rod (refer fig 4b). The printer also uses a belt and pulley mechanism powered by a stepper motor. The head moves left and right along with the movement of the belt.

Fig 4a : Connection between ink tank and print head
Fig 4b : Print head attached to a movable arm

How does the printing process work?

Till now we have learned which components are used in printers. Now I will explain how printing works. As shown in fig 5a, the printhead can print a series of black dots by properly controlling the heating resistors. The printing example is highly simplified for ease of understanding. The actual print head size is a fifth of below showned print head. Here the print head produces 9 lines during a pass, but the actual head produces more than 1000 lines. A roller-stepper motor (refer fig 5b) and two supportive roller arrangements will be used for further printing and movement of paper. This arrangement can move the paper downward. Now, the printer just repeats the above process a number of times until the print finishes.

Fig 5a : Print head releases drops
Fig 5b : Printing the next line with the help of a stepper motor

The modern printers are equipped with clever algorithms which make this process faster. The optimal printing path of a printhead and precise paper roller movement is calculated even before the printing process starts.

The printhead and paper are able to follow such a precise path because they are controlled by a stepper motor and a feedback circuit (refer fig 5b).

That's all in this article. I hope that you have learned the basics of printers. You can read more about inkjet printers & why CMYK colored ink is used in inkjet printers. Please check my next article.

Thank you for reading.


Gaurav Lokhande

Gaurav Lokhande holds B.Tech in electronics & telecommunication engineering. Currently, he is working at Lesics Engineers Pvt.Ltd. as a product developer. His areas of interest are embedded systems, Internet of Things(IoT), and designing of Printed Circuit Board (PCB). To know more about the author check this link.