JP5680614B2 - LED printer head, LED printer, LED printer head control method and program - Google Patents

Description

  The present invention relates to an LED printer head, an LED printer, an LED printer head control method, and a program. Specifically, the present invention relates to a printer head having a plurality of LED elements arranged in a straight line, an LED printer having a photosensitive drum exposed by these LED elements, an LED printer head control method, and a program.

  Conventional general LED printers include a printer head that emits light by LED elements, and a photosensitive drum that is exposed by the printer head. In the printer head, LED chips including a plurality of LED elements are linearly arranged in the main scanning direction. In such an LED printer, a configuration in which all LED elements of the printer head are individually controlled to emit light simultaneously has been used. However, in the configuration in which all the LED elements emit light simultaneously, it is necessary to cope with the increase in the light emission speed accompanying the increase in printing resolution, the enlargement of the circuit scale accompanying the increase in the number of LED elements, and the increase in the number of wire bonding. Is difficult. Therefore, a configuration is used in which the LED elements included in the printer chip are divided into a plurality of blocks, and the plurality of LED elements are sequentially emitted for each block. As such an LED printer, for example, a configuration as disclosed in Patent Document 1 is disclosed.

JP 2002-283609 A

  However, the configuration of Patent Document 1 may cause the following problems. In order to expose the rotating photosensitive drum, the electrostatic latent image formed by the exposure by each LED element belonging to one block is shifted in the sub-scanning direction along the rotation direction of the photosensitive drum. This shift is greatest at the boundary between adjacent blocks. As a result, a step is generated in the latent image at the block boundary. Such a step may appear as streaks or uneven shading due to human visual characteristics. Such a step is not desirable from the viewpoint of printing image quality. In view of the above circumstances, the problem to be solved by the present invention is to provide an LED printer head that can reduce the occurrence of a step in a latent image at the boundary between adjacent blocks during printing.

In order to solve the above problems, the present invention provides an LED chip including a plurality of LED elements arranged in a straight line, a printer head in which the plurality of LED chips are arranged so that the LED elements are arranged in a straight line, comprising a control means for emitting LED elements, and the LED chip, while being divided into a plurality of blocks composed of a plurality of adjacent said LED element, said control means, emission between adjacent contact the block The LED elements sequentially emit light for each block so that the directions are different, and the adjacent LED elements are simultaneously emitted at the boundary of the block , and the adjacent LED elements at the boundary of the block are other LED elements. The amount of light emission is small compared to the above.

  According to the present invention, it is possible to suppress the positional deviation of exposure in the sub-scanning direction at the boundary between adjacent blocks. For this reason, streaks and shading unevenness can be reduced at the position corresponding to the block boundary by reducing the step generated at the position corresponding to the block boundary. As a result, the image quality of printing can be improved.

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of an LED printer. FIG. 2 is a perspective view schematically showing a schematic configuration of a printer head provided in the LED printer. FIG. 3 is a block diagram showing a schematic configuration of an LED printer system. FIG. 4 is a schematic circuit diagram of the LED array mounted on the printer head. FIG. 5 is a timing chart showing the operation of the LED array mounted on the printer head. FIG. 6 is a schematic plan view showing the exposure position by the printer head. FIG. 7 schematically shows an electrostatic latent image formed on the photosensitive drum. FIG. 8A is a plan view schematically showing an electrostatic latent image by a conventional scanning method, and FIG. 8B is a plan view schematically showing an electrostatic latent image by a conventional lighting method. FIG. 8C is a plan view schematically showing the electrostatic latent image according to the present embodiment. FIG. 9A is a graph schematically showing an exposure amount at the boundary between two blocks according to the conventional lighting method, and FIG. 9B is an exposure at the boundary between the two blocks 31a and 31a according to the present embodiment. It is a graph which shows quantity typically. FIG. 10 is a timing chart showing the operation of the LED array mounted on the printer head according to another embodiment.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  First, the overall configuration and overall operation of an LED printer 1 according to an embodiment to which the present invention can be applied will be described with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing a schematic configuration of the LED printer 1. FIG. 2 is a perspective view schematically showing a schematic configuration of the exposure head 3 provided in the LED printer 1. FIG. 3 is a block diagram illustrating a schematic configuration of the LED printer 1 system.

  As shown in FIG. 1, the LED printer 1 includes a photosensitive drum 11 as a photosensitive member, a printer head 3 as a light source, a charging unit 12, a developing unit 13, a transfer unit 14, a cleaning unit 21, and a sheet. The image forming unit includes a cassette 15, a paper feed roller 16, a registration roller 17, a transport unit 18, a fixing unit 19, a paper discharge tray 20, and a printer control unit 6. The photosensitive drum 11 is a rotating body having a photosensitive layer formed on the surface thereof, and rotates at a predetermined speed in the direction of arrow A by a driving mechanism (not shown). The charging unit 12 uniformly charges the surface of the photosensitive drum 11. The printer head 3 irradiates light onto the surface of the photosensitive drum 11 charged by the charging unit 12 to form an electrostatic latent image. Details of the configuration of the printer head 3 will be described later. The developing unit 13 attaches toner to the surface of the photosensitive drum 11 on which the electrostatic latent image is formed, and forms a toner image that follows the electrostatic latent image. Printing paper is stored in the paper cassette 15. The paper feed roller 16 pulls out the printing paper stored in the paper cassette 15 and delivers it to the registration roller 17. The registration roller 17 rotates in synchronization with the rotation of the photosensitive drum 11 and conveys printing paper between the photosensitive drum 11 and the transfer unit 14. The transfer unit 14 transfers the toner image formed on the surface of the photosensitive drum 11 onto the surface of the printing paper conveyed by the registration roller 17. The transport unit 18 transports the printing paper on which the toner image is transferred to the fixing unit 19. The fixing unit 19 fixes the toner image on the printing paper. Then, the printing paper on which the toner image is fixed is discharged to the paper discharge tray 20. The cleaning unit 21 removes toner remaining on the surface of the photosensitive drum 11 after the toner image is transferred to the printing paper. Conventionally known configurations are applied to the photosensitive drum 11, the driving mechanism of the photosensitive drum 11, the developing unit 13, the fixing unit 19, the paper cassette 15, the paper feed roller 16, the registration roller 17, the transport unit 18, and the cleaning unit 21. it can. Therefore, these descriptions are omitted.

  As shown in FIG. 2, the printer head 3 has a plurality of LED chips 4. The plurality of LED chips 4 are mounted so as to be arranged linearly in the main scanning direction (= direction of the rotation axis of the photosensitive drum 11). Each LED chip 4 is provided with a plurality of predetermined LED elements 41. The plurality of LED elements 41 are provided so as to be linearly arranged in the main scanning direction. The LED element 41 of each LED chip 4 constitutes two blocks 31a and 31b adjacent to each other. Specifically, half of the LED elements 41 located on one side of the main scanning direction constitute one block 31a, and half of the LED elements 41 located on the other side constitute the other block 31b. . As described above, the printer head 3 as a whole has a predetermined plurality of LED elements 41 arranged in a straight line in a predetermined direction (here, the main scanning direction). And these predetermined several LED element 41 comprises the blocks 31a and 31b put together for every predetermined plurality. For this reason, in the printer head 3, a plurality of blocks 31a and 31b including a plurality of predetermined LED elements 41 are linearly arranged in a predetermined direction. The number of LED chips 4 mounted on the printer head 3 and the number of LED elements 41 provided on each LED chip 4 are appropriately set according to the printing resolution of the LED printer 1 and the corresponding size of printing paper. There is no particular limitation. Further, the number of blocks 31 a and 31 b provided in one LED chip 4 is not limited to two. A plurality of LED elements 41 arranged in one LED chip 4 may be divided into a plurality of groups, and each of the divided groups may form each block.

  As illustrated in FIG. 3, the printer control unit 6 includes a storage unit 602, a main control unit 601, a temporary storage unit 603, a print data processing unit 604, and a printer head control unit 605. The storage unit 602 stores software (computer program), setting data, and the like for controlling the LED printer 1. The main control unit 601 performs overall control of the LED printer 1. The temporary storage unit 603 can store image data input from the outside. The print data processing unit 604 refers to image data input from the outside or image data stored in the temporary storage unit 603, which is print data (data used by the printer head 3 for exposure) for each scanning cycle (= 1 line). ). The print data includes data indicating whether each LED element 41 emits light for each scanning cycle (P-DATA), exposure amount (ie, print density) data (S-DATA) of each LED element 41, and so on. It consists of two data.

  The printer head control unit 605 includes a clock signal generation unit 606, a start pulse generation unit 607, an LED chip control unit 608 for each LED chip 4, and a print data storage unit 609 for each LED chip 4. The clock signal generator 606 generates a clock signal (CL) used for driving the printer head 3. For the clock signal generator 606, for example, various oscillators are applied. The start pulse generator 607 generates a start pulse (SP) indicating the start of one scanning cycle using the clock signal generated by the clock signal generator 606. For the start pulse generator 607, for example, various frequency dividers are applied. Each print data storage unit 609 temporarily stores a portion of the print data converted by the print data processing unit 604 for use by the corresponding LED chip 4 for each scanning cycle. Each print data storage unit 609 includes a FIFO circuit and a LIFO circuit (or FILO circuit). In either one of the FIFO circuit and the LIFO circuit, print data used for exposure by the LED element 41 included in one block 31a is stored. Moreover, the print data which the LED element 41 contained in the other block 31b uses for exposure is stored in either one. In this manner, each print data storage unit 609 temporarily stores print data used for exposure by the corresponding LED chip 4 and outputs the print data in the opposite order in the two blocks 31. Each LED chip control unit 608 uses the print data stored in the print data storage unit 609, and based on the clock signal generated by the clock signal generation unit 606 and the start pulse generated by the start pulse generation unit 607. The LED chip 4 is controlled and driven.

  In addition, the printer control unit 6 includes a photosensitive drum control unit 611, a charging unit control unit 612, a developing unit control unit 613, a transfer unit control unit 614, a paper feed roller control unit 616, and a registration roller control unit 617. A transport unit control unit 619, a fixing unit control unit 622, and a cleaning unit control unit 621. These control and drive each corresponding part.

  Next, details of the printing operation of the LED printer 1 will be described with reference to FIGS. Here, an example in which one LED chip 4 has 16 LED elements 41 and eight LED elements 41 form one block 31a, 31b is shown as a schematic configuration for explanation. Further, as necessary for description, the LED elements 41 included in one block 31a are denoted by reference symbols a1 to a8, and the LED elements 41 included in the other block 31b are denoted by reference characters b1 to b8 to be distinguished. In addition, this number is an illustration and the number of the LED elements 41 which comprise each block 31a and 31b is not limited. FIG. 4 is a schematic diagram of a circuit configuration of each LED chip 4. FIG. 5 is a timing chart showing the operation of each LED chip 4 mounted on the printer head 3. 6A and 6B are schematic plan views showing exposure positions by the printer head 3, wherein FIG. 6A shows this embodiment and FIG. 6B shows a conventional example. FIG. 7 is a diagram schematically showing an electrostatic latent image formed on the photosensitive drum 11, and is a diagram in which the surface of the photosensitive drum 11 is developed in a plane. FIG. 7A shows this embodiment, and FIG. 7B shows a conventional example.

  As shown in FIG. 4, each LED chip 4 includes a plurality of predetermined LED elements 41 (a1 to a8, b1 to b8) divided into two blocks 31a and 31b, two shift registers 42a and 42b, , Two dimming circuits 43a and 43b, and the same number of and gates 44 and switching circuits 45 as the LED elements 41. Each of the shift registers 42a and 42b functions as a control unit that sequentially delays a plurality of predetermined LED elements 41 to emit light. The LED elements 41 (a1 to a8) included in one block 31a are driven by one shift register 42 and one dimming circuit 43a. The LED elements 41 (b1 to b8) included in the other block 31b are driven by the other shift register 42b and the other dimming circuit 43b. Further, as shown in FIG. 4, the circuit for driving each of the two blocks 31a and 31b is configured to be substantially line symmetric at the boundary between the two blocks 31a and 31b.

  A clock signal is transmitted to each of the shift registers 42 a and 42 b through the clock signal line 46 and a start pulse is transmitted through the start pulse line 47. Each shift register 42a, 42b uses a start pulse as a trigger and outputs a bit signal (strobe signal) that is sequentially delayed in synchronization with the clock signal. Whether each LED element 41 emits light to each AND gate 44 is a bit signal that is sequentially output from each of the shift registers 42a and 42b and print data that is output from the print data storage unit 609. Data (P-DATA) to be shown is input. Data indicating whether each LED element 41 emits light is a serial signal synchronized with the clock signal, and is input to each and gate 44 through each first print data line 48a, 48b. The output from each AND gate 44 is input to the base (gate) of the switching circuit 45. The power line 50 is a line through which a current (VLED) for light emission of each LED element 41 flows, and is connected to each LED element 41 through each switching circuit 45. The dimming circuits 43 a and 43 b receive print data output from the print data storage unit 609 and data (S-DATA) indicating the exposure amount of each LED element 41. The data indicating the exposure amount of each LED element 41 is a serial signal synchronized with data indicating whether or not each LED element 41 emits light, and the dimming circuits 43a and 43b are transmitted through the second print data lines 49a and 49b. Is input. And each light control circuit 43a, 43b controls the exposure amount (For example, the light emission time and the brightness | luminance of each LED element 41) by each LED element 41 according to the input printing data. According to such a configuration, the predetermined number of LED elements 41 included in each of the blocks 31a and 31b emit light sequentially with delay from one end side to the other end side to expose the photosensitive drum 11. As described above, since the circuit configuration for driving each of the blocks 31a and 31b is substantially line symmetrical, the light emitting direction of the LED element 41 is opposite to each other in the two blocks 31a and 31b.

  As shown in FIG. 5, each shift register 42a, 42b operates in synchronization with a start pulse as a trigger, and sequentially delays the LED elements 41 included in the respective blocks 31a, 31b to emit light. Specifically, each shift register 42a, 42b is located at the center in the main scanning direction (= the boundary between the two blocks 31a, 31b) in order from the LED elements 41 (a1, b1) located at both ends in the main scanning direction. The LED elements 41 (a8, b8) to be emitted are sequentially delayed with light emission. For this reason, in each scanning cycle, the two LED elements 41 (a1, b1) located at both ends of each LED chip 4 emit light simultaneously at the same time, and two adjacent LED elements 41 ( a8, b8) finally emit light simultaneously. As described above, the LED elements 41 (a1 to a8) of one block 31a use print data stored in the FIFO circuit, and the LED elements 41 (b1 to b8) of the other block 31b are connected to the LIFO circuit. Use stored print data. With such a configuration, the transmission order of the print data is opposite to each other in the two blocks 31a and 31b. Since the light emission directions of the LED elements 41 are opposite to each other in the two blocks 31a and 31b, the consistency between the print data transmission order and the light emission order of the LED elements 41 (in other words, the exposure position of each LED element 41). Is maintained.

  In the printer head 3, a plurality of LED chips 4 that perform the above operation are arranged linearly in the main scanning direction. Therefore, the light emitting directions of the LED elements 41 in the blocks 31a and 31b are opposite in the adjacent blocks 31a and 31b. The printer head controller 605 controls and drives all the LED chips 4 in synchronization. Therefore, two LED elements 41 adjacent at the boundary of the LED chip 4 simultaneously emit light first in each scanning period. Thus, as a whole, two LED elements 41 adjacent at every other boundary (for example, an odd boundary from one end) of the blocks 31a and 31b initially emit light simultaneously in each scanning period, The LED elements 41 of the adjacent blocks 31a and 31b emit light sequentially delayed toward the opposite sides. And two LED elements 41 which adjoin at every other boundary (for example, even-numbered boundary from one end) of the blocks 31a and 31b simultaneously emit light finally.

  6A and 7A, since the printer head 3 exposes the rotating photosensitive drum 11, the exposure position of each LED element 41 is adjusted as the photosensitive drum 11 rotates. It shifts in the scanning direction. For this reason, as shown in FIG. 7, the electrostatic latent images formed by the blocks 31a and 31b are not parallel to the main scanning direction and are inclined at a predetermined angle. Here, since the light emitting directions of the LED elements 41 of the adjacent blocks 31a and 31b are opposite to each other, the inclination directions of the formed electrostatic latent images are also opposite to each other in the adjacent blocks 31a and 31b. At the boundary between the two blocks 31a and 31b, the two adjacent LED elements 41 emit light simultaneously. For this reason, the electrostatic latent image continues without interruption at the boundary between the blocks 31a and 31b adjacent to each other. Therefore, the electrostatic latent image formed on the photosensitive drum 11 has a shape in which triangular waves continue in the main scanning direction as a whole, and is not interrupted at the boundary between the blocks 31a and 31b. On the other hand, in the conventional example, as shown in FIGS. 6B and 7B, the light emitting directions of the LED elements 41 are the same in all the blocks 31a and 31b. For this reason, in the conventional example, the electrostatic latent image formed on the photosensitive drum 11 is interrupted at the boundary between the blocks 31a and 31b.

  Next, control of the exposure amount at the boundary between the two blocks 31a and 31b will be described with reference to FIGS. FIG. 8A is a plan view schematically showing an electrostatic latent image by a conventional scanning method. FIG. 8B is a plan view schematically showing an electrostatic latent image by a conventional lighting method. FIG. 8C is a plan view schematically showing the electrostatic latent image according to the present embodiment. FIG. 9A is a graph schematically showing the exposure amount at the boundary between two blocks according to the conventional lighting method. FIG. 9B is a graph schematically showing the exposure amount at the boundary between the two blocks 31a and 31a according to the present embodiment. As shown in FIG. 8, the adjacent LED elements 41 in the blocks 31a and 31b have different light emission timings, so that the exposure position is shifted in the sub-scanning direction. On the other hand, at the boundary between the two blocks 31a and 31b, two adjacent LED elements 41 emit light simultaneously, and therefore the exposure positions of these two LED elements 41 are aligned in the sub-scanning direction. As described above, at the boundary between the two adjacent blocks 31a and 31, the exposure position by the adjacent LED element 41 is closer compared to the other portions. For this reason, as shown in FIG. 9A, according to the conventional lighting method, the total exposure amount is higher at the boundary between the two blocks 31a and 31b than at other portions. If it does so, there exists a possibility that unevenness may arise in printed matter. Therefore, as shown in FIG. 9B, in the present embodiment, the light emission of the LED elements 41 (the LED element 41 that emits light first and the LED element 41 that emits light last) located at both ends of each of the blocks 31a and 31b. The amount is made lower than the amount of light emitted from the other LED elements 41. With such a configuration, it is possible to reduce or suppress an increase in the total exposure amount at the boundary between the two blocks 31a and 31b. Therefore, the occurrence of unevenness in the printed material can be reduced or suppressed. It should be noted that how much the light emission amount of the LED element 41 located at both ends of each block 31a, 31b is reduced (correction amount) is appropriately set according to the distance between adjacent exposure positions. This correction amount is stored in the storage unit in advance. Then, when converting the image data into S-DATA, the print data processing unit 604 reads this correction amount and corrects the light emission amounts of the LED elements 41 located at both ends of each of the blocks 31a and 31b. According to such a configuration, the amount of data necessary for correction can be reduced, and the storage capacity of correction amount data can be reduced and the time required for correction can be reduced.

  In addition, the following configuration can be applied to control the exposure amount at the boundary between the two blocks 31a and 31b. FIG. 10 is a timing chart showing the operation of the LED chip 4 mounted on the printer head 3 in another mode of controlling the light emission amount. As shown in FIG. 10, for example, the printer control unit 6 provides a time difference between the adjacent blocks 31a and 31b where the light emission timing of the LED element 41 that emits light first is shifted by one clock. According to such a configuration, the exposure position of the adjacent LED element 41 is shifted in the sub-scanning direction at the boundary between the two blocks 31a and 31b. Accordingly, if the number of LED elements 41 in the blocks 31a and 31b is the same, the exposure position of the last LED element 41 that emits light also shifts in the sub-scanning direction. , Uniform throughout. For this reason, it is possible to reduce or suppress an increase in the total exposure amount at the boundary between the two blocks 31a and 31b (due to the occurrence of a minimum level difference (shift) in the latent image), and to achieve a uniform exposure amount throughout. Can do. Therefore, the occurrence of unevenness in the printed material can be reduced or suppressed.

      According to such a configuration, it is possible to suppress the positional deviation of the exposure in the sub scanning direction at the boundary between the blocks 31a and 31b adjacent to each other. For this reason, the level | step difference which generate | occur | produces in the printed matter in the position corresponding to the boundary of the mutually adjacent blocks 31a and 31b can be reduced. Further, according to such a configuration, it is possible to make the exposure amount uniform at the boundary between the blocks 31a and 31b adjacent to each other. Accordingly, streaks and shading unevenness can be reduced in the printed matter, so that the image quality of printing can be improved.

  In addition, stripes and shading unevenness may occur between the LED chips 4 due to mounting errors in the main scanning direction, but the end LED elements 41 of the LED chips 4 (two adjacent LED elements 41) are turned on simultaneously. Therefore, the main-scanning direction mounting misalignment between the LED chips 4 can be corrected by controlling the light emission amount of the LED element 41.

  Here, an example of the hardware configuration of the printer control unit 6 will be briefly described. The printer control unit 6 is a computer having a CPU, a ROM, and a RAM. The ROM stores a computer program (software) for controlling the LED printer and various setting data. Then, the CPU reads a computer program stored in the ROM and executes it using the RAM as a work area. Further, the CPU refers to various setting data stored in the ROM when executing the computer program. As a result, the functions of the respective units of the printer control unit 6 are realized and the respective processes are executed.

  As mentioned above, although embodiment of this invention was described in detail, the said embodiment only showed the specific example in implementing this invention. The technical scope of the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof, and these are also included in the technical scope of the present invention. For example, contrary to FIGS. 4 and 5, the LED elements 41 of the two blocks 31 a and 31 b configured in one LED chip 4 are located at the center of the LED chip 4 in the main scanning direction (= the boundary between the two blocks 31). May be configured to sequentially emit light from both ends toward the both ends. In short, the light emitting directions of the LED elements 41 belonging to the two adjacent blocks 31a and 31b may be opposite to each other. Moreover, in the said embodiment, although the LED element 41 contained in each LED chip 4 showed the structure divided | segmented into two blocks 31a and 31b, the number of blocks 31a and 31b comprised in each LED chip 4 is shown. The present invention is not limited to the embodiment. Further, the case where the LED chips 4 are arranged linearly in the main scanning direction has been described. However, the present invention is not limited to this case, and the same applies to the case where the LED chips 4 are arranged in a staggered manner.

  Moreover, in the said embodiment, although the structure by which the two blocks 31a and 31b are provided in one LED chip 4 was shown, the number of the blocks provided in one LED chip 4 is not limited. For example, a configuration in which four or six blocks are formed in one LED chip 4 may be employed. The above embodiment only shows two blocks as an example of a plurality of blocks. As long as an even number of blocks are formed in one LED chip, the same effect as described above can be obtained by arranging a plurality of LED chips having the same configuration.

  The present invention is a technique effective as an LED printer. The present invention can be applied not only to a single LED printer but also to a multifunction machine such as a copier or a facsimile.

1: LED printer, 3: Printer head, 31a, 31b: Block, 4: LED chip, 41: LED element, 6: Printer control unit, 605: Printer head control unit

Claims (6)

An LED chip comprising a plurality of LED elements arranged in a straight line;
A printer head in which a plurality of the LED chips are arranged so that the LED elements are arranged in a straight line;
Control means for causing the LED element to emit light;
Have
The LED chip is divided into a plurality of blocks composed of a plurality of adjacent LED elements,
Wherein, said each said block so that the light emission direction is different between the neighboring contact the block LED elements sequentially emit light of and simultaneously emit light the LED elements adjacent at the boundary of the block,
Furthermore, LED elements adjacent at the boundary of the blocks, LED printer head, wherein the light emission amount compared to the other LED elements is small. The control means causes the LED element at one end of the block to emit light first, and causes the LED at the other end to emit light last.
The LED printer head according to claim 1. The light emission amount of each of the LED elements excluding adjacent LED elements at the boundary of the block is equal.
The LED printer head according to claim 1 or 2, wherein An LED printer comprising an image forming unit for writing an electrostatic latent image on a photosensitive member using an LED printer head as a light source,
The LED printer head according to any one of claims 1 to 3 , wherein the LED printer head is an LED printer head. An LED printer head control method comprising:
4. The LED printer head control method according to claim 1, wherein the LED printer head is the LED printer head according to any one of claims 1 to 3 . A program for causing a computer to execute an LED printer head control method,
The LED printer head, a program which is a LED printer head according to any one of claims 1 to 3.