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Principle of dot matrix printer
First, the composition of the dot matrix printer
There are many types of dot matrix printers, and the types are different. Generally, they are divided into two parts: printing mechanism and control and driving circuit. The stylus printer has three movements during normal operation, namely the lateral movement of the print head, the longitudinal movement of the printing paper, and the needle movement of the print needle. These movements are all controlled by software, driven by some precision machinery.
1. Machinery
The printing mechanism mainly includes a word car and a transmission mechanism, a printing needle control mechanism, a ribbon driving mechanism, a paper feeding mechanism and a printer status sensor, and these mechanisms are precision mechanical devices to ensure various mechanisms can realize the following various movements.
(1) Word car and transmission mechanism The word car is the carrier of the print head. The print head moves horizontally left and right through the carriage drive system, and then the print pin hits the ribbon to print. The power source of the word car generally uses a stepping motor, and the rotation of the stepping motor is changed into the lateral movement of the word car through the transmission device. It is generally driven by a wire rope or a synchronous toothed belt.
(2) Print pin control mechanism The print pin is the key to correct printing. The print pin control mechanism realizes the needle exiting and pinching action of the print needle. The action of the print needle is usually controlled by the electromagnetic principle.
(3) Ribbon drive mechanism The print needle strikes the ribbon, and the ink on the ribbon prints characters or graphics on the paper. During the printing process, when the print head moves left and right, the ribbon drive mechanism drives the ribbon to rotate at the same time, continuously changing the position where the ribbon is hit by the printing needle, and ensuring uniform wear of the ribbon, thereby extending the ribbon. The service life ensures that the printed characters or graphics are evenly colored.
The ribbon drive mechanism generally uses a carriage motor to drive a synchronous toothed belt (such as LQ-1600K) or a steel (nylon) wire rope to drive the ribbon shaft to rotate. It can also be driven by two separate motors (such as some color printers). The ribbon is moving in the forward and reverse directions.
(4) Paper feed mechanism This mechanism realizes the longitudinal movement of the printing paper. When a line is printed, it is wrapped by paper. The paper feeding method generally includes friction paper feeding, gear feeding, and platen roller feeding. The power mode is to convert the rotation of the stepping motor into a paper moving movement by the traction mechanism.
(5) Printer status sensor The settings of the sensor are different for different printers. Usually there is the original position sensor (whether the detection car stops at the original position on the left), the paper end sensor (detects whether the loaded paper is used up, the alarm is used up), the timing sensor (detects the instantaneous position of the car) and the machine Cover status sensor (detects abnormal opening of the printer cover during printing) and so on.
Control and drive circuit
(1) Control circuit The control circuit of the current popular printer has adopted the microcomputer structure, so the printer is also a complete microcomputer. Divided from the processor category, it is composed of a single-chip extended memory and interface circuit, and also uses a CPU (for processor) design. From the composition structure, there is a single CPU structure, but also a master-slave CPU process control structure. Various controls on the printer are made through software. A small array of fonts and control programs are stored in the ROM, and user-defined characters are stored in the line buffer RAM.
(2) Drive circuit The function of the drive circuit is to drive the paper feed motor, the carriage motor and the print pin out of the needle by the high voltage under the control of the control circuit.
(3) Interface circuit The connection between the printer and the host computer has a serial interface, a parallel interface, and a USB interface.
(4) DC voltage regulator circuit Provides various DC power supplies for the printer.
Second, the working principle of the dot matrix printer
(1). Overview
The printer itself is a microcomputer system, and the whole machine is controlled by the CPU. Its control program is stored in the ROM, so that the CPU can be turned on to work. The CPU can receive various control commands of the panel, and can also receive instructions from the host and interpret and execute various instructions. These connections are made through the interface of the computer. There are two ways to work with the needle, Text Mede and Bit Image Print Mode.
1. Text mode
The print data of the dot matrix printer is obtained from the host through an interface with a computer. The print data obtained by the printer is the ASCII code of the characters to be printed. These ASCII codes are stored in the print buffer in the printer. After the host transfers the data to the print buffer, the printer sends a "BUSY" signal to the host. After receiving the signal, the host pauses sending data, and the printer starts printing.
After the printing starts, the CPU in the printer takes out the ASCII code of the printed character from the print buffer, and calculates the first address of the character dot matrix storage area corresponding to the character. The dot code of each column is taken out one by one by address, the print pin is driven, the ribbon is struck, and printed characters are formed on the printing paper. In the character generator ROM of the printer, there are usually 96 kinds of ASCII codes and some special characters of the font code (some printers also have Chinese character dot matrix codes, such as LQ-1600K). When the data in the buffer is printed, the printer is opened again, receiving new print data from the host, and starting a new printing process.
If it is necessary to print a graphic or a Chinese character (for a printer without a Chinese character font), the pixel signal or the Chinese character font code of the graphic can be sent by the host. Obviously, this way of printing is similar to how the display displays characters.
2. Bit image mode
In this mode, the print data sent by the computer is the data for controlling the needle and pin of the print pin, so the programmer can directly write a program to control each print pin to print out graphics, tables and Chinese characters.
(2). The working principle of the print head
The main component of a dot matrix printer is the printhead. The commonly used 9-, 16-, and 24-pin printers refer to the number of print pins on the printhead. The print head can be divided into a screw type, a snap type, an energy storage type, a sound factor type, and a piezoelectric type according to the type of the shot. Here we use the 24-pin printer LQ-1600K and AR3240 print head as an example to illustrate its working principle. The figure below shows the working principle of the LQ-1600K print head, which is a snap-on print head. In front of each print pin (looking forward from the back of the print pin) there is a loop of iridium iron, surrounded by 12 coils and 12 print pins (LQ1600K print head is divided into two layers, each layer 12 The root print needle has 12 long needles on the upper layer and 12 short needles on the lower layer. 12 print needles on each layer are evenly arranged on the circumference of the loop, and are pierced on the top of the print head along the guide grooves on the guide plate to form two rows. Print pins arranged in parallel.
Usually, the printing needle is in the state of leaving the driving coil by the elastic force of the return spring. When the driving coil passes the current, the armature of the tail of the printing needle is excited to move toward the driving coil, and at the same time, the printing needle is driven to collide with the ribbon along the multi-layer guiding plate to make the color The belt and the printing paper are pressed against the reel. At this time, the ink on the ribbon is infiltrated onto the printing paper by the impact of the printing needle, leaving a small dot. When the current in the drive coil disappears, the print pin is reset to the original state by the return spring, completing a printing action. This type of snap-on print head has a fast acceleration of the printing needle and a high frequency of the needle. Since the printing needle is divided into two layers, it is more convenient to replace the printing needle, and the long needle can be used as a short needle.
Behind each print pin (looking forward from the back of the print pin) there is a loop of ferrules, surrounded by 24 degaussing coils, 24 armature springs and 24 print pins. The 24 print pins are evenly arranged on the circumference of the ring and are passed through the guide grooves on the guide plate at the top of the print head to form two rows of print pins arranged in parallel.
The working principle of the energy storage type print head is to use a permanent magnet to act on the spring, so that the printing needle is in the storage state in the printing head, that is, the printing needle stores the striking energy, and when the degaussing coil is energized, the permanent magnet magnetic field is generated. The magnetic field in the opposite direction reduces the magnetic flux of the permanent magnet, which cancels the attraction of the permanent magnet to the rear armature and the spring piece of the printing needle, so that the spring piece drives the printing needle to fly forward and complete the printing operation. The advantages of this type of printhead are low power consumption and fast printing speed.
Basic knowledge of ribbon
First, the role of ribbon in the printer
The dot matrix printer uses the dot matrix striker in the printer head to strike the print ribbon and produce a print effect on the paper. It can be seen that the ribbon plays the role of consumables in this process, and the quality of the ribbon will directly affect the printing effect and even the life of the print head.
Good Ribbon = Excellent Print Effect = Long Life of Printer
The most important factor in determining the print quality and service life of a dot matrix printer is the quality of the print ribbon. High-quality ribbons can generally print more than 3 million characters, while inferior ribbons can only print about 100,000 to 200,000 characters. Normal use, the difference between the two is tens of times larger.