Structure and principle of printer

Printer is a complex and precise mechanical and electronic device, and no matter what kind of printer, its structure can basically be divided into two parts: mechanical device and control circuit, which are closely related. Mechanical devices include print head, carriage mechanism, paper feeding mechanism, ribbon transmission mechanism, ink (toner) supply mechanism and selenium drum transmission mechanism. They are all actuators of the printer system, which are coordinated and controlled by the control circuit. The control circuit of printer includes CPU main control circuit, drive circuit, input and output interface circuit and detection circuit.

Although the appearance of the printer is ever-changing, the printed graphics and colors are also different. According to its principle, we can divide the commonly used printers into three types: needle printers, inkjet printers and laser printers.

The structure and working principle of three printers are briefly introduced.

The working principle of the stylus printer is that the code sent by the host computer is sent to the main control circuit of the printer after being processed by the input interface circuit of the printer. Under the control of the control program, the code of characters or graphics is generated, and the print head is driven to print a column of dot matrix graphics. At the same time, the carriage moves laterally to generate column spacing or word spacing, and then the next column is printed, column by column; After printing a line, start the paper feeding mechanism to feed paper to generate line spacing, and at the same time, the print head returns to a new line to print the next line; Repeat the above process until printing is completed.

The key to the name of a stylus printer lies in the structure of its print head. The structure of print head is complex, which can be roughly divided into printing needle, driving coil, positioner, excitation disk and so on. To put it simply, the working process of the print head is as follows: when the print head gets a current pulse from the driving circuit, the driving coil of the electromagnet generates a magnetic field, which attracts the armature of the printing needle, drives the printing needle to hit the ribbon, and prints a dot pattern on the printing paper. Because the printing needle directly performs the printing function, this printer is called a stylus printer.

The working principle of inkjet printer is basically the same as that of stylus printer, and the essential difference between them lies in the structure of print head. The print head of an inkjet printer consists of hundreds of ink channels with extremely small diameters (about several microns). The number of these channels, that is, the number of spray holes of the inkjet printer, directly determines the printing accuracy of the inkjet printer. An execution unit capable of generating vibration or heat is attached in each channel. When the control circuit of the print head receives the driving signal, these execution units are driven to vibrate, and the ink in the channel is squeezed and ejected; Or generate high temperature to heat the ink in the channel, generate bubbles, and eject the ink from the nozzle; The ejected ink reaches the printing paper, and the printing paper produces graphics! This is the basic principle of piezoelectric and bubble inkjet print heads. The control principle and working mode of inkjet printer are basically the same as those of stylus printer, so I won't go into details here!

Structure and working principle of laser printer.

When the computer host sends data to the printer, the printer first temporarily stores the received data in the cache, and then sends it to the printer's processor after receiving a complete piece of data. The processor organizes these data into a signal stream, which can drive the print engine to work. For a laser printer, this signal stream is a set of pulse signals that drive the laser head to work.

The core technology of laser printer is the so-called electronic imaging technology, which combines the principles and technologies of imaging and electronics to generate images. The core component is photosensitive selenium drum. The laser emitted by the laser transmitter shines on a prism-shaped reflector. With the rotation of the mirror, the light sweeps from one end of the drum to the other end in turn (there are various focusing lenses in the middle, which makes the spot scanned on the surface of the drum very small). The toner cartridge rotates in steps of 1/300 inches or 1/600 inches, and the scanning is performed on the next line. The selenium drum is a cylinder coated with organic material, which is charged in advance. When there is light irradiation, the resistance of the irradiated part will change. The data signal sent by the computer controls the laser emission. The light scanned on the surface of the toner cartridge is constantly changing. Some places are irradiated, the resistance becomes smaller and the charge disappears. Others have no light, but the charge still exists. Finally, a latent image composed of charges is formed on the surface of the toner box.

Toner is a kind of tiny plastic particles with charge, and its charge is opposite to that on the surface of toner box. When the charged toner box surface passes through the developing roller, the charged part absorbs toner particles, and the latent image becomes a real image. When the drum rotates, another conveying system feeds the printing paper. After passing through a set of electrodes, the printing paper is charged with the same polarity, but much stronger than the surface of the drum. Then the paper passes through the toner drum with toner, and the toner on the surface of the toner drum is attracted to the printing paper to form an image on the surface of the paper. At this time, the toner and the printer are combined only by the attraction of electric charges. Before the printing paper is sent out of the printer, the plastic toner is heated and melted at high temperature, and fixed on the surface of the paper when it is cooled.

After the toner is transferred to the printing paper, the surface of the toner drum continues to rotate, and the remaining toner is removed by the cleaner, thus entering the next printing cycle.

As can be seen from the above principles, the essential difference between a laser printer and a stylus printer and an inkjet printer is that a laser printer prints a whole page at a time, which is page by page; However, both stylus printers and inkjet printers print one line at a time instead of one line at a time. Therefore, under the same printing requirements, the printing speed of laser printers is faster than that of needle printers and inkjet printers, which is also an advantage of laser printers.

Characteristics and application scope of three kinds of printers

Because the stylus printer adopts mechanical impact print head, it has strong penetration, can print multi-layer carbon paper, has copying function, and can also print infinite continuous paper. The consumables used are ribbons, which are the cheapest among the three printers. Its disadvantages are large volume and weight, high printing noise, low precision and slow speed, and generally there is no function of printing color images. It is suitable for professional applications with special requirements, such as finance, taxation and financial institutions. Common models are LQ series of Epson, such as LQ-680k；; STAR's AR and CR series, such as ar-6400, etc.

Ink-jet printers have high printing accuracy, can usually print color images, and can be made very small in size and weight.

You can even print with you, and the noise is very small when printing. But consumables-ink is the most expensive of the three printers! And if you want to print a beautiful image, you need to use the same expensive special printing paper to have a good printing effect. So the use cost of inkjet printers is very high! At the same time, it does not have the function of copying and printing continuous paper. Suitable for occasions with high printing quality but small quantity, such as home and small office. Common models include Epson STYLUS PHOTO series, such as STYLUS PHOTO 900；; Canon I series, such as i6500, i355, etc.

The printing accuracy of laser printers is also very high, which is basically not much different from that of inkjet printers. It uses consumables-selenium drum, and its cost is between needle printer and inkjet printer. You can also print color images, and the requirements for printing media are not as high as those of inkjet printers. The printing speed is the fastest among the three printers, and the noise is very small. But the volume and weight are larger than those of inkjet printers. Can only print page by page, there is no function of copying and printing continuous paper. It is suitable for occasions with large printing volume and heavy tasks, such as large commercial organizations and design and printing fields. Common models include HP LaserJet series, such as LaserJet 10 10, color LaserJet 8550, etc.

Common faults of printers and their solutions

Printer is a kind of precision equipment with mechanical and electrical integration, and its structure is generally complicated. Compared with other external devices of the computer, the failure rate is also higher, but it is usually easier to deal with. Here, the common faults and solutions of the three models are introduced respectively.

Common faults of stylus printer

Compared with the other two printers, the mechanical parts of the needle printer account for the largest proportion in the machine, so there are many mechanical problems, especially the main operating parts, such as the print head, carriage mechanism, paper feeding mechanism and so on.

The printing work of the stylus printer is ultimately completed by the print head, which is the most arduous part of its workload, so it is also the most prone to problems. The common problems of print head are broken needle, blurred printing and so on.

The broken needle of the print head is characterized by the obvious appearance of one or several cycloids on each line of printed text, or the lack of certain horizontal strokes. To judge whether the needles are broken, it is necessary to remove the back cover of the print head and press the armature of each needle to see if there are any needles protruding from the front of the print head. If there is no needle protruding, it can be considered that the needle is broken, which can generally be solved by replacing it with a new needle. Of course, it is also possible that every needle is normal, but there are similar broken needles. This is usually caused by an open or short circuit of the needle drive coil of the print head or a failure of the needle drive circuit. It is necessary to check the above circuit parts, so I won't go into details here.

The print head of a stylus printer has a heavy task, so after a period of use, the print head may be blocked by dirt, resulting in blurred printing; However, the printing needle may also be shortened due to mechanical wear, resulting in a decrease in impact force and unclear performance. In case of jam, the print head can be soaked in absolute alcohol and cleaned by ultrasonic cleaner. When the needle is worn, we can try to adjust the distance between the print head and the paper properly. If the fault is not obviously improved, we can only replace the print head. Of course, the old ink-free ribbon, or the distance between the print head and the paper is too far, may also lead to fuzzy printing, but this is not the problem of the print head itself, and can be solved by replacing the new ribbon or adjusting the distance.

The needle printer prints line by line, and the carriage mechanism will move back and forth once every line is printed. Therefore, the carriage mechanism is also a high-risk component. Common faults include misplacement of printed words, collision between cars and walls, abnormal movement of cars, etc.

The printed text is staggered up and down, which shows that the starting position of the printed text is not fixed. After printing one or several lines of text, the starting position is shifted to the left or right, and the offset distance is uncertain, resulting in the text being staggered up and down and unreadable. The carriage moves abnormally, such as the carriage can't run or the running speed is uneven, the carriage can't return to its original position after power-on, and the print head doesn't press the Enter key or presses the Enter key abnormally when printing. One of the most basic and direct reasons for the above problems is that the motor of the character car is overloaded. This is generally because the guide rail of the carriage is too dirty or rusty, which makes the resistance of the carriage moving back and forth too large or uneven, resulting in the above problems. To solve the above problems, it is generally necessary to clean the carriage guide rail and add high-quality lubricating oil. In severe cases, it is necessary to separate the carriage mechanism from the guide rail and clean the sliding bearing part of the carriage to ensure the free operation of the carriage. After this treatment, dislocation and abnormal walking can be basically solved.

When the carriage hits the wall, it means that the printer continues to move forward after the carriage returns to the left boundary during printing, and the carriage motor makes abnormal noise when it hits the left boundary. This is usually because the printer's initial position sensor does not detect the character tray. In general, it is only necessary to adjust the sensor slightly to the right, and in a few cases, the detection circuit should be checked. Of course, too much resistance of the guide rail of the Chinese character car will also lead to the failure of hitting the wall.

In addition, the damage of the motor or drive circuit of the character car may cause the above faults, so it is necessary to check the above circuit parts at this time.

Compared with the print head and carriage mechanism, the paper feeding mechanism has less load and lower failure rate, such as no paper feeding, uneven paper feeding and paper shortage.

The reasons for non-paper feeding or uneven paper feeding are usually the damage of paper feeding motor or driving circuit, transmission mechanical failure, mismatch of driving software, etc. Generally speaking, there are many cases where the paper feeding motor is damaged, usually because the user turns the paper feeding handle by hand when the power is on, or forcibly tears the paper during normal printing, which leads to the overload and burning of the paper feeding motor. At this time, when the power is cut off, you can obviously feel a slight vibration, which is very different from the sense of stability when the motor rotates normally. Generally, replacing the paper feed motor can solve the problem. The faults of mechanical parts are mostly caused by loose meshing between transmission gears or gear wear and slip. At this time, it is necessary to carefully observe the transmission mechanism, reposition the misplaced and fallen gears or replace the worn gears. Most of the nonstandard paper feeding of printers is due to mismatched driver software. As long as the printer self-check test and direct text printing under online DOS are done well, if the paper can be fed normally, it can be determined that there is no hardware fault in the printer, and the problem lies in the driver software.

Paper shortage means that after the printer is turned on and loaded with printing paper, the panel still shows the paper shortage status, so it is impossible to print online. At this time, it is very important to check the paper sensor and its circuit. Paper sensors generally have mechanical switch type and photoelectric coupling type. Mechanical switch type, easy to contact badly after long-term use, leading to the detection of paper. At this time, it is necessary to clean or replace the sensor. For photoelectric coupling, pay attention to whether the sensor slot is blocked by dust, and generally clean it up to solve the problem.

Common faults of inkjet printer

Similar to the stylus printer, the print head of the inkjet printer is also the heaviest part of its work, so there are also the most problems, such as blurred printing handwriting and broken printing lines.

Most of the reasons for the above problems are that the printer has not used or added non-original ink for a long time, which leads to obstacles in the ink delivery system or blockage of the nozzle (that is, the print head). Usually, the elimination method is cleaning operation. If the traffic jam is serious, it is necessary to remove the nozzle, soak it in pure water at about 50-60℃ and clean it with an ultrasonic cleaner. Be sure to dry it after cleaning. If there is still no obvious effect after repeated cleaning, it means that the nozzle hole has been blocked, and only the nozzle can be replaced at this time. There is another situation, that is, the service life of the nozzle is up, and the accuracy of the nozzle hole is greatly reduced, resulting in blurred printing. Generally speaking, for Epson's inkjet printer, the life of the nozzle is about 20-30 ink cartridges; For Canon, the service life of the ink cartridge nozzle using 10 or so is coming.

There are many problems in the cleaning pump nozzle of inkjet printer, which is also one of the main factors causing blockage. The nozzle of printer cleaning pump plays a decisive role in the protection of printer nozzle. After the nozzle trolley returns to its original position, the nozzle of the cleaning pump is used for weak pumping treatment and sealing protection of the nozzle. When a new ink cartridge is installed in the printer or the nozzle is damaged, the suction pump at the lower end of the machine will use it to pump air to the nozzle. The higher the working accuracy of this nozzle, the better. However, in actual use, its performance and air tightness will be reduced due to the extension of time and the increase of dust and ink residue in this mouth. If the user does not check or clean frequently, it will cause the nozzle of the printer to have a fault similar to blockage. So keep this part all the time. The specific method is: take off the upper cover of the printer, take off the trolley, and use the needle tube to inhale pure water for washing, especially to fully clean the microporous gasket embedded in the mouth. Need to remind users in particular that when cleaning this part, never use ethanol or methanol to clean it, which will make the microporous gasket embedded in this part dissolve and deform, and never let lubricating oil contact with the pump nozzle, which will deform the rubber sealing ring at the pump nozzle and fail to seal and protect the nozzle.

For Epson's inkjet printer, it is also common that when the printer is turned on after replacing the new ink cartridge, the "out of ink" light on the printer panel is on. Under normal circumstances, when the ink runs out, the "Out of Ink" light will light up. After replacing the new ink cartridge, the "Out of Ink" light on the printer panel is still on. This kind of failure may occur. One is that the ink cartridge is not installed or there is something wrong with the ink cartridge itself and the detection circuit. The other is to take down the old ink cartridge and replace it with a new one when it is turned off. Because after replacing the ink cartridge, the printer will fill the ink feeding system, and this process will not be carried out when it is turned off, so the printer cannot detect the reinstalled ink cartridge. In addition, some printers use the electronic counter inside the printer to count the ink capacity (especially when counting the usage of color ink). When the counter reaches a certain value, the printer judges that the ink is exhausted. During the process of replacing the ink cartridge, the printer will reset its internal electronic counter to confirm the installation of the new ink cartridge. If a new ink cartridge is replaced when the machine is turned off, the counter in the printer cannot be reset, so "Out of Ink" will still be reported. The solution is to reinstall the ink cartridge in the startup state. But if the fault still exists, you must try to replace a normal ink cartridge, and verify whether it is the ink cartridge problem or the detection circuit problem.

Similar to Epson printers, Canon and HP inkjet printers can't detect ink cartridges, but unlike Epson, the nozzles of these two brands of inkjet printers can be disassembled and replaced independently, and generally the nozzles and ink cartridges are integrated. Therefore, the problem that the ink cartridge can't be detected is mostly because the electrical contacts on the cartridge holder where the ink cartridge is installed are polluted or corroded by ink, resulting in poor contact with the ink cartridge, so the ink cartridge can't be detected. The solution is to clean the contacts with alcohol or replace the cartridge holder.

Because both inkjet printers and stylus printers print line by line, their carriage mechanism and paper feeding mechanism are very similar, and the problems are similar, so I won't go into details here.

Common faults of laser printer

Compared with the other two printers, the mechanism of laser printer is more complicated and its faults are more complicated. The following briefly introduces some common faults.

Paper jam of laser printer

The most common fault of laser printer is paper jam. When this fault occurs, the indicator light on the operation panel will flash and send an alarm signal to the host. The way to eliminate this fault is simple, just open the cover and take off the paper jam. However, it should be noted that the paper must be taken in the paper feeding direction, and no knob can be turned in the opposite direction. But if there is frequent paper jam, it is necessary to check the paper feed channel. Pick-up wheel is the most easily worn part of laser printing. When the paper in the paper tray is normal and it is impossible to take the paper, it is often that the paper roller is worn or the paper pressing spring is loose, and the pressure is not enough, so that the paper cannot be fed into the machine. At this time, it is generally necessary to replace the paper roll. In addition, improper installation of paper tray and poor paper quality (too thin, too thick and wet) may also cause paper jam or paper retrieval failure.

Laser printer output blank

The reason for this failure may be that the developing roller does not absorb toner (the DC bias of the developing roller is not applied), or the toner drum is not grounded. Because the negative charge cannot be discharged to the ground and the laser beam cannot act on the photosensitive drum, it is impossible to print words on paper. If the photosensitive drum does not rotate, it will not produce images and will not be transmitted to the paper, so it is necessary to determine whether the photosensitive drum can rotate normally. Disconnect the printer power supply, take out the toner cartridge, open the notch on the box cover, mark the non-photosensitive part of the photosensitive drum, and reload it into the machine. Turn it on for a while, then take out the inspection mark to see if it has moved, so as to judge whether the photosensitive drum works normally.

If the toner cannot be supplied normally or the laser beam is blocked, it will also cause blank paper. Therefore, it is necessary to check whether the toner is used up, whether the ink cartridge is correctly loaded into the machine, whether the sealant tape has been removed or whether there are any obstacles in the laser irradiation channel. It should be noted that the power supply must be turned off during inspection, because the laser beam is harmful to the eyes.

Print paper output turns black.

When the primary corona discharge fails or the control circuit fails, the laser keeps emitting, which will cause the printed content to be completely black. At this time, you should check whether the corona discharge wire is disconnected or corona high voltage exists, and whether the beam detector in the laser beam path works normally, because these aspects are directly related to the output effect. This problem is complicated to solve, and it is generally not recommended for novices to fix it themselves.

The output handwriting is very weak.

There is little toner in the toner box, the developing voltage of the developing roller is low, or the toner is unpolarized and charged, so it can't be transferred to the photosensitive drum, which will all cause the phenomenon that the printing handwriting becomes weak. Take out the toner cartridge and shake it gently. If the printing effect does not improve, replace the toner cartridge or ask professional maintenance personnel to handle it. In addition, some printers have a switch under the toner box, which can adjust the laser intensity to match the photosensitive sensitivity of toner. If this switch is set incorrectly, it will also lead to weak printing handwriting.

Vertical white stripes appear when outputting.

If there is dirt on the reflector installed above the photosensitive drum, the dirt on the mirror surface of the laser will be absorbed and cannot reach the photosensitive drum, thus forming a narrow white stripe on the printing paper. Observe the laser transmission channel carefully and clean it up to solve the problem.

When the transfer roller is installed under the printing paper channel, it will also attract dust and paper scraps, and some parts will become dirty or polluted, thus preventing the toner from being transferred from the toner box to the printing paper, and also causing a narrow white stripe to be formed on the printing paper. When the toner cartridge is out of order, the handwriting will generally fade in a large area. Remove the toner cartridge and gently shake it to make the toner in the cartridge evenly distributed. If the improvement is still not great, the toner cartridge will be replaced.

One-sided blackening of printing paper

When the laser beam scanning is beyond the normal range, the position of the reflector above the photosensitive drum changes, and the toner box fails, and the toner is concentrated on one side of the box, which may lead to unilateral blackening of the printer. Check the position of the laser channel and its reflector, correct the deviation or remove the toner cartridge and gently shake it to make the toner in the toner cartridge evenly distributed. If it still cannot be improved, please replace the toner cartridge. Is the solution to unilateral blackening.

Repeated stains on printing paper

When a piece of paper passes through the printer, about 12 kinds of rollers in the printer rotate more than once. The largest toner drum rotates 2 to 3 times, and the feed roller may rotate more than 10 times. When there are equally spaced dirty marks on the paper, it may be caused by dirty or damaged rollers. Suppose there is a stain on a roll, if the stain is close, it may be formed by a small roll; When the distance is far away, check the larger drum. Measure the distance between dirty marks, and then calculate the roller diameter that causes dirty marks with the following formula: roller diameter = dirty mark distance/π; So as to judge which drum caused the problem, and then clean or replace it, and the problem can be solved.

In addition to the unique faults of the above three printers, they also have some common faults, such as unable to print or print garbled codes online, unable to start (that is, no power supply) and so on.

Generally speaking, there are several reasons why it is impossible to print or print garbled codes online: the printing line between the printer and the computer is not well connected, so it is necessary to turn off the power supply of the computer and the printer and reconnect it firmly; If the printing cable is defective, it can be tested on a normal machine to verify whether there are any defects. If it proves to be defective, replace the cable with a new one. The wrong printer is selected in the software. You need to check the printer selection menu of the software to see if you have selected the right printer. The printer port is not configured correctly. Check the configuration menu of the software to ensure that the correct printer port is accessed. If the computer you are using is not a parallel port, make sure that the printer cable is connected to the correct port. The most serious situation is that there is something wrong with the interface circuit of the printer, which is usually caused by plugging and unplugging the print line when the printer is turned on. In a few cases, it may also be caused by lightning strike or electrification of the electric ground wire. Interface circuit faults are usually serious and need mainboard level maintenance, so I won't go into details here.

The problem of no power supply is usually caused by unstable power supply voltage, long-term continuous work and poor ventilation, which leads to overheating damage of power supply and generally requires board-level maintenance. It should be noted that many printers, especially inkjet and small laser printers, do not have a hard power switch. As long as the power cord is connected, the power supply part will always work, so it is easy to burn out the power supply when the voltage is high at night. Therefore, we suggest that users should disconnect the power supply if they don't use the printer for a long time, so as to avoid failure after a long time.

A printer is a highly sophisticated device. When in normal use, you should try to stay away from the high temperature and dusty working environment and do some maintenance as often as possible, such as cleaning the carriage guide rail, oiling and lubricating. Only a good working environment and careful maintenance can ensure the long-term normal use of the machine.