JP2006159851A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an image forming device which can also form the image of a lower resolution than that of a predetermined sub-scanning direction. <P>SOLUTION: The image forming device comprises an LED printer head having a plurality of LED elements which irradiate light to a photo conductor which moves in the sub-scanning direction with constant speed and in which each LED element thereof is arranged in a main-scanning direction in the condition that it shifts one by one to the sub-scanning direction by the pitch corresponding to the 1st resolution; and an image development control part which drives each LED element by the driving period and the exposure time of the line period corresponding to the 1st resolution, wherein when exposure is performed in the 2nd resolution of 1/n (n is an even number) of the 1st resolution, the image development control part drives each LED element making the LED driving period T2b of each LED element to be the period of 1/n of the line period T1b of the 2nd resolution and making the exposure time to be the time of n times of the 1st resolution. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including an LED printer head as exposure means.

  In an image forming apparatus using an electrophotographic system, an electrostatic latent image is formed by exposing the surface of a uniformly charged photoreceptor corresponding to image data to form an electrostatic latent image. Is developed into a toner image, and the toner image is transferred to a recording medium and fixed. Conventionally, an exposure light source that uses a laser or an LED (Light Emitting Diode) element is known, and an image forming apparatus that uses an LED element as an exposure light source has LED elements set in advance along the main scanning direction. A plurality of LED printer heads are arranged in accordance with the resolution, and the LED printer head drives and controls the LED elements in accordance with image data in units of one scanning line.

  In the image forming apparatus including such an LED printer head, the resolution of the LED printer head is fixed to a preset resolution. Therefore, a set resolution designated by a host device such as a PC (Personal Computer), an LED, When the resolution of the printer head is not the same as that of the printer head, there is a problem that printing cannot be performed at the resolution intended by the host device.

Therefore, a control command processing unit that receives a control command including distance information based on the resolution from the host device and executes processing corresponding to the instruction of the control command, and information holding for setting and storing assumed resolution information that the host device assumes in advance Distance information corrected by the correction means, and a correction means for correcting the control command processing from the assumed resolution information and the actual resolution information. Discloses a printer system that generates image information to be printed (see Patent Document 1).
Japanese Patent Laid-Open No. 10-138552

  By the way, in recent years when high image quality and high quality are required, it is very difficult physically and in manufacturing to arrange a number of LED elements corresponding to high resolution in the main scanning direction. An LED printer head having a plurality of LED head modules is devised. For example, each LED head module is arranged at predetermined intervals in the main scanning direction with the LED elements sequentially shifted in the sub-scanning direction at a pitch corresponding to a preset resolution, and sequentially time-division driven in the main scanning direction. It is configured to be. An image formed by an image forming apparatus that employs an LED printer head configured in this way, when the resolution in the sub-scanning direction is lower than the preset resolution, one scanning line does not become a straight line. There exists a problem that it will become step shape according to arrangement | positioning of an LED element.

  However, Patent Document 1 is print correction for the resolution in the main scanning direction, and does not mention the case of printing at a lower resolution than the preset resolution in the sub-scanning direction.

  An object of the present invention is to realize an image forming apparatus capable of forming an image having a resolution lower than a preset resolution in the sub-scanning direction.

  The invention described in claim 1 has a plurality of LED elements for irradiating light to a photosensitive member moving in the sub-scanning direction at a constant speed, and each LED element in the sub-scanning direction at a pitch corresponding to the first resolution. LED printer heads arranged in the main scanning direction in a sequentially shifted state, and LED drive control means for driving each LED element with a drive period and exposure time of a line period corresponding to the first resolution. In the image forming apparatus, when the LED drive control unit performs exposure at a second resolution of 1 / n (n is an even number) of the first resolution, the drive cycle of each LED element is a line cycle at the second resolution. The image forming apparatus is characterized in that the LED element is driven with a period of 1 / n of 1 and an exposure time of n times the first resolution.

  The invention according to claim 2 has a plurality of LED elements for irradiating light to the photosensitive member moving in the sub-scanning direction at a constant speed, and each LED element in the sub-scanning direction at a pitch corresponding to the first resolution. LED printer heads arranged in the main scanning direction in a sequentially shifted state, and LED drive control means for driving each LED element with a drive period and exposure time of a line period corresponding to the first resolution. In the image forming apparatus, when the LED drive control unit performs exposure at a second resolution of 1 / n (n is an even number) of the first resolution, the LED drive control unit includes the LED elements within the line period of the second resolution. The LED element is driven n times with a drive cycle of 1 / n of a line cycle at the second resolution and an exposure time of the exposure time of the first resolution. It is formed device is characterized.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, when the LED drive control unit performs exposure at a second resolution of 1 / n (n is an even number) of the first resolution, It has a storage means for holding image data at the time of the first LED driving, and reads the image data in the storage means at the second and subsequent LED driving to drive the LED element.

  According to the first aspect of the present invention, it is necessary to form one scanning line by changing the driving cycle and the exposure time of the LED element without changing the linear velocity and the LED driving frequency of the image forming apparatus. It is possible to realize an image forming apparatus capable of easily forming a second resolution image having a lower resolution than the preset first resolution in the sub-scanning direction while ensuring a sufficient exposure time.

  According to the second aspect of the present invention, one scanning line is formed by changing the driving cycle and the number of driving times of the LED elements without changing the linear velocity of the image forming apparatus and the exposure time for each driving cycle. Therefore, it is possible to realize an image forming apparatus capable of easily forming an image having a second resolution lower than the first resolution in the sub-scanning direction which is set in advance while ensuring an exposure time necessary for the purpose.

  According to the third aspect of the present invention, the same effect as that of the second aspect can be obtained, and the operation of acquiring the image data is not required every time the LED printer head is driven. Simplification can be performed.

[Embodiment 1]
Hereinafter, Embodiment 1 of the present invention will be described in detail with reference to the drawings.
First, the configuration will be described.
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus 1 according to the first embodiment.
The image forming apparatus 1 receives an image data from a copy function for reading an image from a document and forming the read image on a recording medium P such as paper, or a host device such as a PC, and displays an image represented by the image data as a recording medium. This is a digital multifunction machine having a printer function and the like that is formed on P and output. As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 10 and a printing unit 20.

The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder) and a reading unit 12.
The automatic document feeder 11 includes a paper feed roller 11a that sequentially conveys documents stacked on the document tray 11g from the top, and a contact roller 11b that allows the document to pass while contacting the contact glass that is a document reading portion. And a guide roller 11c for guiding the document conveyed by the paper feed roller 11a along the contact roller 11b. A switching claw 11d for switching the transport direction of the document that has passed through the contact glass, a reversing roller 11e for reversing the front and back of the document, and a discharge tray 11f for discharging the document that has been read are provided.

  The reading unit 12 includes a scanner including a light source, a lens, a contact glass, a CCD (Charge Coupled Device), etc., and forms an image of the reflected light of the light irradiated on the original and photoelectrically converts the original image of the original. (Analog image signal) is read, A / D converted and subjected to various image processing, and then output to the printing unit 20 as print data. Here, the image means not only image data such as graphics and photographs but also text data such as characters and symbols.

  The print unit 20 performs electrophotographic image formation based on input print data, and includes an image forming unit 30, a cleaning unit 40, a paper feeding unit 50, a transport unit 60, and a fixing unit. 70.

The image forming unit 30 includes a photosensitive drum 31, a charging device 32, an LED printer head 33 as an exposure device, a developing device 34, and a transfer device 35.
Specifically, the photosensitive drum 31 charged by the charging device 32 is irradiated with light from the LED printer head 33 to form an electrostatic latent image. Then, the developing device 34 forms a toner image by attaching charged toner to the surface of the photosensitive drum 31 on which the electrostatic latent image is formed. The toner image formed on the photosensitive drum 31 by the developing device 34 is transferred to the recording medium P by the transfer device 35.

  The LED printer head 33 is configured by arranging a plurality of light emitting diode (LED) elements in the axial direction (main scanning direction X) of the photosensitive drum 31, and is supplied by an image development control unit described later. It is selectively driven according to image data (data signal).

  After the toner image is transferred to the recording medium P, the cleaning unit 40 removes residual charges, residual toner, and the like on the surface of the photosensitive drum 31.

The paper feed unit 50 includes a plurality of paper feed trays 51 and a manual feed tray 52.
The paper feed tray 51 accommodates recording media P identified in advance for each size and type for each paper feed tray 51, and the recording media P accommodated by the paper feed rollers 51a are conveyed one by one from the top. Transport toward 60.
The manual feed tray 52 can be loaded with various types of recording media P according to the needs of the user each time, and the recording media P loaded by the paper feed rollers 52a are fed one by one from the top to the transport unit 60. Transport toward.

  The transport unit 60 transports the recording medium P transported from the paper feed tray 51 or the manual feed tray 52 to the transfer device 35 via a plurality of intermediate rollers 61a, 61b, 61c and a registration roller 62.

  The fixing unit 70 thermally fixes the toner image transferred to the recording medium P transported by the transport unit 60. The recording medium P that has been subjected to the fixing process is output between the paper discharge rollers 63 and the paper output tray 64.

  The rotational operation speeds (hereinafter referred to as linear speeds) of the photosensitive drum 31 and the fixing unit 70 of the image forming apparatus 1 are controlled by a main body control unit described later.

FIG. 2 shows a plan view of the configuration of the LED printer head 33.
The LED printer head 33 is composed of a plurality of LED head modules 33a arranged in the main scanning direction X. The LED head module 33a has a predetermined interval in the main scanning direction X in a state in which the plurality of LED elements are sequentially shifted in the sub scanning direction at intervals (pitch) corresponding to a preset resolution (first resolution) in the sub scanning direction. The plurality of LED elements are configured to be sequentially time-divisionally driven in the main scanning direction X.

  The LED head module 33a shown in FIG. 2 is arranged at predetermined intervals in the main scanning direction X in a state where the first to eighth LED elements L1 to L8 divided into eight in the main scanning direction X are sequentially shifted in the sub-scanning direction Y. Then, the first LED element L1 is sequentially driven into eight divisions. By sequentially driving the first to eighth LED elements L1 to L8 at equal intervals, a latent image of one scanning line is written on the photosensitive drum 31.

  For example, when the LED head module 33a shown in FIG. 2 is an LED head module 33a corresponding to a resolution in the main scanning direction X of 1200 [dpi] and a resolution in the sub scanning direction (first resolution) of 2400 [dpi], Since the pixel pitch in the scanning direction Y is 10.5 [μm], the distance from the first LED element L1 to the eighth LED element is 10.5 [μm], and the distance between the LED elements is 1.5 [μm]. The LED elements are arranged at predetermined intervals in the main scanning direction X with the LED elements sequentially shifted in the sub-scanning direction Y.

  As described above, in the LED head module 33a in which the resolution in the sub-scanning direction is set to 2400 [dpi], the LED element is moved every time the position of the photosensitive drum 31 with respect to the LED head module 33a moves 1.5 [μm]. When sequentially driven and driven from the first LED element L1 to the eighth LED element L8 (the position of the photosensitive drum 31 with respect to the LED printer head 33 moves 10.5 [μm]), one scanning line is formed. Therefore, the drive cycle of the LED elements of the LED head module 33a for forming one scan line of 2400 [dpi] (hereinafter referred to as the LED drive cycle) is such that the position of the photosensitive drum 31 with respect to the LED printer head 33 is 10. This is the time required to move 5 [μm].

  However, when the LED printer head 33 having the LED head module 33a as shown in FIG. 2 is used to perform exposure with a resolution of 1200 [dpi] in the sub-scanning direction, the pixel pitch in the sub-scanning direction Y is 21.0 [μm]. Since the LED elements are sequentially driven every time the position of the photosensitive drum 31 relative to the LED head module 33a moves by 3.0 [μm], one scanning line does not become a straight line, depending on the arrangement of the LED elements. In order to solve this problem, the present invention controls the drive timing of the LED element.

FIG. 3 shows a control block diagram of the image forming apparatus 1.
As shown in FIG. 3, the image forming apparatus 1 includes a main body control unit 100, a mechanism control unit 200, an image development control unit 300, an I / F 401, and the like, and these units are connected by a bus 402 as a communication unit. .

  The main body control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, an HDD (Hard Disk Drive) 105 connected via an I / F 104, and the like. Yes.

  The CPU 101 reads the system program, each processing program, and data stored in the ROM 102 and develops them in the RAM 103 or the HDD 105, and centrally controls the operation of each part of the image forming apparatus 1 according to the developed programs. Timing control of the entire system, print data storage and storage control using the RAM 103 or HDD 105, image processing (magnification, filter, γ conversion, etc.) of print data sent from the image reading unit 10 and the like for the print unit 20 It performs input / output control of image data, interface (I / F) with other applications (FAX, printer, scanner, etc.) and operation control.

  The CPU 101 also receives print data transmitted from a PC (Personal Computer) 2 via the I / F 401, temporarily stores the received print data in the RAM 103 or the HDD 105, and stores image data based on the print data. The image is developed on the image development control unit 300. The CPU 101 causes the image development control unit 300 to develop the image data, and then outputs a start instruction signal to the mechanism control unit 200 to start each unit of the image forming apparatus.

  The ROM 102 stores programs and data corresponding to the image forming apparatus 1 in advance, and stores a system program, various processing programs corresponding to the system, and data necessary for processing by the various processing programs.

  The RAM 103 and the HDD 105 serve as temporary storage areas for programs, input, or output data and parameters read from the ROM 102 in various processes controlled and executed by the CPU 101.

  The mechanism control unit 200 comprehensively controls each drive mechanism and various sensors in the image forming apparatus 1 based on signals from the main body control unit 100. For example, the mechanism control unit 200 rotates the photosensitive drum 31 at a constant speed. The motor M to be driven is controlled. When the mechanism control unit 200 receives the activation instruction signal from the main body control unit 100, the image development is performed on the sub-scanning activation signal VV corresponding to the size of the recording medium and the line synchronization signal HV synchronized with the linear velocity of the photosensitive drum 31. Output to the controller 300.

  The image development control unit 300 outputs various signals to the LED printer head 33 based on the image data received from the main body control unit 100 and the sub-scanning activation signal VV and the line synchronization signal HV received from the mechanism control unit 200. The head 33 is driven.

  The I / F 401 is configured to include various interfaces such as a network interface card (NIC), a modem (MODEM: Modulator-DEModulator), and a USB (Universal Serial Bus), and an external device (such as a PC 2) on the network. Send and receive information to and from each other.

  The LED printer head 33 includes an LED element mounting substrate 33b on which a plurality of LED head modules 33a are mounted, an optical system such as a SELFOC lens array 33c for imaging light from the LED elements on the photosensitive drum 31, an LED An element drive / light quantity correction circuit unit 330 is provided.

  The LED element driving / light quantity correction circuit unit 330 is a circuit that performs light quantity correction and driving operation of each LED element based on a signal input from the image development control unit 300.

  LED elements are subject to the same conditions due to variations in mechanical and electrical characteristics during manufacture of LED elements, variations in current resistance of LED element drive circuits, electrical variations in mounting members (LED element mounting substrate 33b, etc.), etc. It is known that a difference occurs in the amount of light of each LED element even if it is driven by. Therefore, the LED element drive / light quantity correction circuit unit 330 corrects the current amount and the rising drive characteristic (ON timing) for each LED element so that the variation in the light quantity of the entire LED printer head 33 falls within a certain range. A correction unit is provided, and the correction unit corrects the light amount of each LED element according to the light amount correction data input from the image development control circuit unit 300.

  Further, the LED element driving / light quantity correction circuit unit 330 includes a buffer memory as a storage unit that temporarily stores image data corresponding to each LED element, and is based on a signal input from the image development control unit 300. Image data is written and erased in the buffer memory corresponding to each LED element.

FIG. 4 shows a configuration diagram of the image development control unit 300.
As illustrated in FIG. 4, the image development control unit 300 includes a clock timing generation control unit 301, a light amount correction data memory 302, an image data memory 303, a data selector unit 304, and a system I / F 305.

  The clock timing generation control unit 301 outputs the clock signal CLK and the timing signal to the light amount correction data memory 302 and the data selector unit 304 according to the sub-scanning activation signal VV and the line synchronization signal HV input from the mechanism control unit 300. Do.

  The light amount correction data memory 302 stores light amount correction data for each LED element in advance to correct the light amount of each LED element, and is input from the clock timing generation control unit 301 before the LED printer head 33 is driven. The light quantity correction data of each LED element is output to the data selector unit 304 in accordance with the timing signal.

  The image data memory 303 stores image data expanded to a resolution based on the print data via the system I / F 305, and sequentially supplies image data (data signal DATA) for one scanning line to the data selector unit 304. Output.

  The data selector unit 304 is an LED element driving / light amount correction circuit according to the timing signal input from the clock timing generation control unit 301 and the light amount correction data input from the light amount correction data memory 302 before the LED printer head 33 is driven. The light amount correction data is transmitted to the correction unit of each LED element of the unit 330, and the variation in the light amount of the entire LED printer head 33 is corrected.

  Then, the data selector unit 304 corrects the variation in the light amount of the entire LED printer head 33, and then the data signal DATA input from the image data memory 303 in accordance with the clock signal CLK input from the clock timing generation control unit 301. The line clear signal LCLR, the selection signal SK, the LED synchronization signal HVL, and the LED drive signal LON are output to the LED element drive / light quantity correction circuit unit 330.

  In order to realize the first embodiment, the image development control circuit unit 300 is based on the resolution of the image data received from the main body control unit 100 and the line cycle T1 of the line synchronization signal HV received from the mechanism control unit 200. The LED drive cycle T2 of the LED synchronization signal HLV and the ON time (exposure time) of the LED drive signal LON are changed and set.

  When the image development control circuit unit 300 performs exposure at the second resolution, which is 1 / n times the first resolution in the sub-scanning direction (where n is an even number), the image development control circuit unit 300 is within the line period T1 at the second resolution. The LED driving control means drives the LED element with the LED driving cycle T2 as a cycle 1 / n times the line cycle T1 in the second resolution and the exposure time as n times the first resolution.

Hereinafter, in the first embodiment, the first resolution is 2400 [dpi], the second resolution is 1200 [dpi], which is half the resolution of the first resolution, and the resolution in the sub-scanning direction shown in FIG. A change setting operation of the LED driving cycle T2 and the exposure time when the LED printer head 33 including a plurality of LED head modules 33a set to 2400 [dpi] is used will be described.
Note that the resolution in the main scanning direction is constant (1200 [dpi]).

  FIG. 5 shows an example of a timing chart of various signals when an image having a resolution in the sub-scanning direction of 2400 [dpi] is exposed.

As shown in FIG. 5, at time t1, the sub-scan activation signal VV rises.
At time t2 after the sub-scan activation signal VV rises, the line synchronization signal HV rises, and after the line synchronization signal HV rises, the line clear signal LCLR rises. When the line clear signal LCLR rises, the data signal DATA temporarily stored in the buffer memory in the LED element driving / light quantity correction circuit unit 330 is erased.

  After the erasing of the data signal DATA in the buffer memory is completed, the data signal DATA for one scanning line is sequentially stored in the buffer memory of each LED element in synchronization with the clock signal CLK. At time t4 after the data signals DATA from the first LED element L1 to the eighth LED element L8 are stored, the line synchronization signal HV rises in order to store the data signal DATA of the next line.

  At time t3, the LED synchronization signal HVL rises in order to drive each LED element in accordance with the data signal DATA of each buffer memory, and the selection signal SK for selecting the LED element to be driven rises sequentially. After the selection signal SK rises, the LED drive signal LON sequentially rises according to the selection signal SK, and sequentially drives the LED elements at equal intervals.

  One scan line is formed by sequentially driving the first LED element L1 to the eighth LED element L8 at equal intervals. At time t5 after the eighth LED element L8 is driven, the LED synchronization signal HVL for forming the next line rises, and the next scan line is formed.

  The pixel pitch in the sub-scanning direction Y of the LED elements arranged on the LED printer head 33 is equal to the resolution in the sub-scanning direction of the image to be formed (the sub-scanning resolution of the image is 2400 with respect to the LED printer head 33 in FIG. 2). [dpi]), the LED drive cycle T2a from time t3 to time t5 is set to the same time (T1a = T2a) as the line cycle T1a from time t2 to time T4.

  The time during which the LED drive signal LON is kept rising (ON time) is the time during which a latent image is written on the photosensitive drum 31, that is, the exposure time. In FIG. 5, the exposure time when the sub-scanning resolution is 2400 [dpi] is A.

  FIG. 6 shows an example of a timing chart of various signals when an image having a resolution of 1200 [dpi] in the sub-scanning direction is exposed in the first embodiment.

  As shown in FIG. 6, the line synchronization signal HV has a resolution (1200 [dpi]) that is 1/2 the resolution in the sub-scanning direction (2400 [dpi]) set in advance in the sub-scanning direction. The line period T1b is twice the line period T1a with a resolution in the sub-scanning direction of 2400 [dpi].

  Similarly to the exposure operation of 2400 [dpi], when the LED element is driven by dividing the line period T1b into eight, a linear scanning line cannot be obtained, resulting in a staircase scanning line. Therefore, the image development control unit 300 is driven so that the LED element is driven with an LED drive period T2b (T2b = T1b / 2) that is ½ of the line period T1b and an exposure time (2A) that is twice as long as 2400 [dpi]. Controls the timing of various signals.

At time t11, the sub-scan activation signal VV rises.
At time t12 after the sub-scan activation signal VV rises, the line synchronization signal HV rises, and after the line synchronization signal HV rises, the line clear signal LCLR rises. When the line clear signal LCLR rises, the data signal DATA temporarily stored in the buffer memory in the LED element driving / light quantity correction circuit unit 330 is erased.

After the erasing of the data signal DATA in the buffer memory is completed, the data signal DATA for one scanning line is sequentially stored in the buffer memory of each LED element in synchronization with the clock signal CLK.
The time for which the data signal DATA is stored in the buffer memories corresponding to the first LED element L1 to the eighth LED element L8 is within ½ of the line period T1b.

  At time t13, the LED synchronization signal HVL rises and the selection signal SK rises sequentially in order to drive each LED element according to the data signal DATA of each buffer memory. The selection signal SK rises so that each LED element is selected at equal intervals (8 divisions) within a time ½ times the line cycle T1b. After the selection signal SK rises, the LED drive signal LON is selected. The LED elements sequentially rise in response to the signal SK, and the LED elements are sequentially driven at equal intervals.

  The first LED element L1 to the eighth LED element L8 are sequentially driven at equal intervals with a half period of the line period T1b, so that a scanning line with a resolution of 1200 [dpi] in the sub-scanning direction becomes a straight line. At time t14 after the eighth LED element L8 is driven, the LED synchronization signal HVL rises, but since the line clear signal LCLR has not risen, the exposure operation for the next scan line is not performed.

  The pixel pitch in the sub-scanning direction Y of the LED elements arranged in the LED printer head 33 is ½ times the resolution in the sub-scanning direction of the image to be formed (relative to the LED printer head 33 in FIG. When the sub-scanning resolution is 1200 [dpi]), the LED drive cycle T2b from time t13 to time t14 is set to a time half of the line cycle T1b from time t12 to time T15 (T2 = T1 / 2). Is done.

  In the case of exposing an image with a resolution of 1200 [dpi] in the sub-scanning direction, the exposure time B in FIG. 6 is that the exposure area per pixel is twice the resolution of 2400 [dpi] in the sub-scanning direction. The exposure time B requires twice as long as the exposure time A when exposing an image having a resolution of 2400 [dpi] in the sub-scanning direction.

  Therefore, in FIG. 6, when the exposure time when the sub-scanning resolution is 1200 [dpi] is B, the exposure time B when the sub-scanning direction resolution is 1200 [dpi] is 2400 [dpi]. The exposure time A is set to twice as long.

Next, the exposure time will be described with a specific example.
First, when the LED printer head 33 including a plurality of LED head modules 33a in which the resolution in the sub scanning direction is set to 2400 [dpi] shown in FIG. 2 is used, the resolution in the main scanning direction is 1200 [dpi] and the sub scanning is performed. An exposure time B in the case where the direction resolution is 1200 [dpi] will be described.

  The exposure time B calculated below is the exposure time required when writing a solid image latent image on the photosensitive drum 31.

  As a method for calculating the exposure time B, an electrophotographic process condition using a laser light source having the same wavelength is used, the light amount is measured on the surface of the photosensitive drum 31 with the laser light source having the same wavelength, and the necessary exposure energy is estimated. Use the method. This method is effective for obtaining an approximate value of the exposure time as the control time. However, in order to determine the final electrophotographic process conditions, it is necessary to adjust the exposure time by performing test pattern exposure, measuring the potential of the photosensitive drum, and the like.

  In the calculation, the linear velocity v of the photosensitive drum 31, the laser emission wavelength w, and the LED element light quantity lw are set as follows.

  In addition, as a convention in the specifications of LED printer head specifications, it is customary to use [W] as the light quantity notation unit of the LED element. However, in order to explain the calculation format accurately in the explanation of the exposure time. , [W] is written as [J / s].

Linear velocity of the photosensitive drum 31: v = 420 [mm / s]
Laser emission wavelength: w = 760 ± 10 [nm]
Light quantity of LED element: lw = 1 [μJ / sdot] ([μW / dot])

  The writing frequency f when the resolution in the main scanning direction is 1200 [dpi] and the resolution in the sub-scanning direction is 1200 [dpi] and the laser power P required to move the charge charged on the photosensitive drum are as follows: Value.

Writing frequency: f = 107.4578 [MHz]
Laser power: P = 288 [μJ / s] ([μW])

In the case where the output resolution is 1200 [dpi] in the main scanning direction × 1200 [dpi] in the sub-scanning direction, the exposure energy E ₁₂₀₀ required per dot is calculated from the following equation (1).

E ₁₂₀₀ = P × (1 / f) (1)
= 2.68 [pJ / dot]

The exposure time B is calculated from the exposure energy E ₁₂₀₀ obtained by the equation (1), the light amount lw of the LED element, and the following equation (2).

B = E ₁₂₀₀ ÷ lw (2)
= 2.68 [μs]

  When the resolution in the main scanning direction is 1200 [dpi and the resolution in the sub-scanning direction is 1200 [dpi], the line period T1b is the resolution 1200 [dpi] in the sub-scanning direction, the linear velocity v of the photosensitive drum 31, and the following equation: Calculated from (3).

T1b = 25.4 ÷ 1200 ÷ v (3)
= 50.4 [μs]

  In the case where the LED head module 33a drives the first to eighth LED elements L1 to L8 into eight divisions to form one scanning line, the maximum time (maximum driving time) Bmax that the LED element can be driven is equal to the line period T1b. It is calculated from the division number m and the following equation (4).

Bmax = T1b ÷ m (4)
= 6.3 [μs]

  Accordingly, when the resolution in the main scanning direction is 1200 [dpi] and the resolution in the sub-scanning direction is 1200 [dpi], the exposure time B is 5.3 [%] of the line period T1b and the maximum driving time Bmax is 42.5. The exposure energy necessary for writing the latent image can be ensured in the time of [%].

  Next, when the LED printer head 33 including a plurality of LED head modules 33a in which the resolution in the sub-scanning direction is set to 2400 [dpi] shown in FIG. 2 is used, the output resolution is 1200 [dpi] in the main scanning direction. The exposure time A when the resolution in the sub-scanning direction is 2400 [dpi] will be described.

When the resolution in the main scanning direction is 1200 [dpi] and the resolution in the sub-scanning direction is 2400 [dpi], the exposure area is 1200 [dpi] in the main scanning direction and the resolution in the sub-scanning direction is 1200 [dpi]. In this case, the exposure energy E _{2400 in} the case of a resolution of 2400 [dpi] in the sub-scanning direction required per dot is ½ times that in the case of the resolution in the sub-scanning direction of 1200 [dpi]. It can be assumed that the exposure energy E ₁₂₀₀ is ½ times.

E ₂₄₀₀ = E ₁₂₀₀ ÷ 2
= 1.34 [pJ / dot]

  The exposure time A is calculated from the exposure energy E2400, the light amount lw of the LED element, and the following equation (5).

B = E ₂₄₀₀ ÷ lw (5)
= 1.34 [μs]

  In the case of resolution 1200 [dpi] in the main scanning direction × resolution 2400 [dpi] in the sub-scanning direction, the line period T1a is the resolution 1400 [dpi] in the sub-scanning direction, the linear velocity v of the photosensitive drum 31, and the following formula ( 6).

T1a = 25.4 ÷ 2400 ÷ v (6)
= 25.2 [μs]

  In the case where the LED head module 33a drives the first to eighth LED elements L1 to L8 into eight parts to form one scanning line, the maximum time (maximum driving time) Amax that the LED element can be driven is equal to the line period T1a. It is calculated from the division number m and the following equation (7).

Amax = T1a ÷ m (7)
= 3.15 [μs]

  Therefore, when the resolution in the main scanning direction is 1200 [dpi] and the resolution in the sub-scanning direction is 2400 [dpi], the exposure time A is 5.3 [%] of the line period T1a and the maximum driving time Amax is 42.5. The exposure energy necessary for writing the latent image can be ensured in the time of [%].

  Therefore, even when the resolution change in the sub-scanning direction (change of 1200 [dpi] and 2400 [dpi]) is performed, the line period is changed proportionally and the exposure time is also changed proportionally. And an appropriate exposure time can be ensured by using the same LED printer head 33.

  Thus, the exposure time required to form one scan line by changing the LED drive cycle T2 and the exposure time of the LED elements without changing the linear velocity v and the LED drive count of the image forming apparatus 1. Image formation that can easily form an image with a second resolution (1200 [dpi]) having a lower resolution than the first resolution (2400 [dpi]) in the sub-scanning direction set in advance while ensuring B (B = 2A) An apparatus can be realized.

[Embodiment 2]
Hereinafter, the second embodiment of the present invention will be described in detail with reference to the drawings.
First, the configuration will be described.

  The cross-sectional configuration of the image forming apparatus 1 according to the second embodiment, the configuration of the LED printer head 33, the control block configuration of the image forming apparatus 1, the configuration of the image development control unit 300, and the image with a resolution in the sub-scanning direction of 2400 [dpi] In the example of the timing chart of various signals when exposing the light and the specific example of the exposure time, only portions different from those in the first embodiment will be described, and illustration and description thereof will be omitted.

  In order to realize the second embodiment, the image development control circuit unit 300 is based on the resolution of the image data received from the main body control unit 100 and the line cycle T1 of the line synchronization signal HV received from the mechanism control unit 200. The LED drive cycle T2 of the LED synchronization signal HLV and the ON time (exposure time) of the LED drive signal LON are changed and set.

  When the image development control circuit unit 300 according to the second embodiment performs exposure at a second resolution that is 1 / n times (n is an even number) resolution set in advance in the sub-scanning direction, Within the line cycle T1 in the resolution, the LED element is driven n times with the LED drive cycle T2 being a cycle that is 1 / n times the line cycle in the second resolution and the exposure time being the exposure time A of the first resolution. LED drive control means.

Hereinafter, in the second embodiment, the first resolution is 2400 [dpi], the second resolution is 1200 [dpi] which is ½ times the first resolution, and the resolution in the sub-scanning direction shown in FIG. A change setting operation of the LED driving cycle T2 and the exposure time when the LED printer head 33 including a plurality of LED head modules 33a set to 2400 [dpi] is used will be described.
The resolution in the main scanning direction is constant (1200 [dpi]).

  FIG. 7 shows an example of a timing chart of various signals when an image having a resolution of 1200 [dpi] in the sub-scanning direction is exposed in the second embodiment.

  As shown in FIG. 7, the line synchronization signal HV has a resolution of 1200 [dpi] in the sub-scanning direction, so the line period T1b is twice the line period T1a with a resolution in the sub-scanning direction of 2400 [dpi]. Become.

  Similarly to the exposure operation of 2400 [dpi], when the LED element is driven by dividing the line period T1b into eight, a linear scanning line cannot be obtained, resulting in a staircase scanning line. Therefore, within the line cycle T1b of 1200 [dpi], the LED drive cycle T2b (T2b = T1b / 2) that is ½ times the line cycle T1b, and the exposure time A is 2400 [dpi]. The image development control unit 300 controls the timing of various signals so that the LED element is driven twice.

At time t21, the sub-scan activation signal VV rises.
At time t22 after the sub-scan activation signal VV rises, the line synchronization signal HV rises, and after the line synchronization signal HV rises, the line clear signal LCLR rises. When the line clear signal LCLR rises, the data signal DATA temporarily stored in the buffer memory in the LED element driving / light quantity correction circuit unit 330 is erased.

After the erasing of the data signal DATA in the buffer memory is completed, the data signal DATA for one scanning line is sequentially stored in the buffer memory of each LED element in synchronization with the clock signal CLK.
The time during which the data signal DATA is stored in the buffer memories corresponding to the first LED element L1 to the eighth LED element L8 is within a time that is ½ times the line cycle T1b.

  At time t23, the LED synchronization signal HVL rises and the selection signal SK rises sequentially in order to drive each LED element according to the data signal DATA of each buffer memory. The selection signal SK rises so that each LED element is selected at equal intervals (8 divisions) within half the time of the line cycle T1b. After the selection signal SK rises, the LED drive signal LON is changed to the selection signal SK. In response, the LED elements are sequentially raised to drive the LED elements.

  The first LED element L1 to the eighth LED element L8 are sequentially driven at equal intervals with a half period of the line period T1b, thereby forming a scanning line with a resolution of 1200 [dpi] in the sub-scanning direction.

  After the data signal DATA is stored in the buffer memories corresponding to the first LED element L1 to the eighth LED element L8, at time T24, the line clear signal LCLR rises, and the buffer memory in the LED element drive / light quantity correction circuit unit 330 The data signal DATA temporarily stored therein is erased.

  After the erasing of the data signal DATA in the buffer memory is completed, the data signal DATA for one scanning line is sequentially stored in the buffer memory of each LED element in synchronization with the clock signal CLK. Since it has not risen, the same data signal DATA is stored again.

  At time t25 after the eighth LED element L8 is driven, since the LED synchronization signal HVL rises and the line clear signal LCLR rises, the exposure operation from time t23 to t25 is based on the data stored in the buffer memory. Similarly, the exposure operation is repeated again between times t25 and t27.

  The pixel pitch in the sub-scanning direction of the LED elements arranged in the LED printer head 33 is ½ times the resolution in the sub-scanning direction of the image to be formed (the image sub-scanning with respect to the LED printer head 33 in FIG. When the scanning resolution is 1200 [dpi]), the LED drive period T2b of the time (T2b = T1b / 2) that is ½ the line period T1b is twice in the line period T1b from time t22 to time T26. Repeated.

  When an image with a resolution of 1200 [dpi] in the sub-scanning direction is exposed using the LED printer head 33 of FIG. 2, the exposure area per pixel is twice the resolution of 2400 [dpi] in the sub-scanning direction. Thus, the exposure time when the resolution in the sub-scanning direction is 1200 [dpi] requires twice the exposure time A when the resolution in the sub-scanning direction is 2400 [dpi].

  However, since the LEDs are driven twice within the line cycle T1b, the exposure time for each LED drive cycle T2b may be the same exposure time A as the resolution 2400 [dpi] in the sub-scanning direction. When the resolution in the scanning direction is changed from 2400 [dpi] to 1200 [dpi], one scanning line is formed by changing the number of times of LED driving without changing the exposure time for each LED driving cycle. The exposure time B (B = 2A) necessary for this can be ensured.

  FIG. 8 shows an example of a timing chart of various signals when an image having a resolution in the sub-scanning direction of 1200 [dpi] is exposed in the second embodiment.

  The timing chart of various signals when exposing an image with a resolution of 1200 [dpi] in the sub-scanning direction shown in FIG. 8 is a timing chart for reading and exposing the data signal stored in the buffer memory when the LED is driven for the second time. Yes, the description of the same operation as in FIG. 7 is omitted, and only the different operation will be described.

  After the data signal DATA is stored in the buffer memories corresponding to the first LED element L1 to the eighth LED element L8, the repeat signal RP falls at time T34, and the buffer memory in the LED element drive / light quantity correction circuit unit 330 The data signal DATA temporarily stored therein is read again.

  At time t25 after the eighth LED element L8 is driven, the LED synchronization signal HVL rises, and the exposure operation is repeated again based on the read data.

  In this way, when the configuration is such that the data in the buffer memory is read again, the operation of acquiring the image data (data signal DATA) is not required every time the LED printer head is driven as shown in FIG. Simplification can be performed.

  By changing the LED driving cycle T2 and the number of times of driving without changing the linear velocity v and the exposure time for each LED driving cycle of the image forming apparatus, the exposure time B (B required for forming one scanning line is changed. = 2A) and an image forming apparatus capable of easily forming an image with a second resolution (1200 [dpi]) having a lower resolution than the preset first resolution (2400 [pi]) in the sub-scanning direction. can do.

  In the first and second embodiments, exposure is performed at a second resolution that is a resolution (1200 [dpi]) that is ½ times the preset first resolution (2400 [dpi]) in the sub-scanning direction. However, since it is clear that the same effect can be obtained even when the second resolution is 1 / n times (n is an even number), the description is omitted.

  Further, the present invention is not limited to the contents of the above embodiment, and can be appropriately changed without departing from the gist of the present invention.

1 is a cross-sectional configuration diagram of an image forming apparatus 1 according to a first embodiment. 3 is a plan view of the configuration of an LED printer head 33. FIG. 2 is a control block diagram of the image forming apparatus 1. FIG. 3 is a configuration diagram of an image development control unit 300. FIG. It is an example of a timing chart of various signals when an image having a resolution of 2400 [dpi] in the sub-scanning direction is exposed. 4 is a timing chart example of various signals when an image having a resolution of 1200 [dpi] in the sub-scanning direction is exposed in the first embodiment. 10 is a timing chart example of various signals when an image having a resolution in the sub-scanning direction of 1200 [dpi] is exposed in the second embodiment. 12 is another example of a timing chart of various signals when an image having a resolution in the sub-scanning direction of 1200 [dpi] is exposed in the second embodiment.

Explanation of symbols

1 Image forming apparatus 2 PC
DESCRIPTION OF SYMBOLS 10 Image reading part 11 Automatic document feeding part 11a Paper feed roller 11b Contact roller 11c Guide roller 11d Switching claw 11e Reverse roller 11f Paper discharge tray 11g Document tray 12 Reading part 20 Printing part 30 Image forming part 31 Photosensitive drum 32 Charging device 33 LED printer head 33a LED head module 33b LED element mounting substrate 33c Selfoc lens array 34 Development device 35 Transfer device 40 Cleaning unit 50 Paper feed unit 51 Paper feed tray 51a, 52a Paper feed roller 52 Manual feed tray 60 Transport units 61a, 61b, 61c Intermediate roller 62 Registration roller 63 Paper discharge roller 64 Paper discharge tray 100 Main body control unit 101 CPU
102 ROM
103 RAM
104 I / F
105 HDD
200 Mechanism control unit 300 Image development control unit 301 Clock timing generation control unit 302 Light amount correction data memory 303 Image data memory 304 Data selector unit 305 System I / F
330 LED element drive / light quantity correction circuit unit 401 I / F
402 Bus

A, B Exposure time CLK Clock signal DATA Data signal HV Line synchronization signal HVL LED synchronization signal L1-L8 1st-8 LED element LCLR Line clear signal LON LED drive signal M Motor RP Repeat signal SK Select signal T1, T1a, T1b Line cycle T2, T2a, T2b LED drive cycle VV Sub-scan start signal

Claims (3)

It has a plurality of LED elements for irradiating light to a photoreceptor that moves in the sub-scanning direction at a constant speed, and each LED element is sequentially shifted in the sub-scanning direction at a pitch corresponding to the first resolution in the main scanning direction. An image forming apparatus comprising: an LED printer head that is arranged; and an LED drive control unit that drives each LED element at a drive period and an exposure time of a line period corresponding to the first resolution.
When the LED drive control means performs exposure at a second resolution of 1 / n (n is an even number) of the first resolution, the drive cycle of each LED element is 1 / n of the line cycle of the second resolution. Driving the LED element with a period and an exposure time of n times the first resolution;
An image forming apparatus. It has a plurality of LED elements for irradiating light to a photosensitive member moving in the sub-scanning direction at a constant speed, and each LED element is sequentially shifted in the sub-scanning direction at a pitch corresponding to the first resolution in the main scanning direction. An image forming apparatus comprising: an LED printer head that is arranged; and an LED drive control unit that drives each LED element at a drive period and an exposure time of a line period corresponding to the first resolution.
When the LED drive control means performs exposure at a second resolution of 1 / n (n is an even number) of the first resolution, the drive cycle of each LED element is set within the line cycle at the second resolution. Driving the LED element n times with a period of 1 / n of the line period in two resolutions and an exposure time of the exposure time of the first resolution;
An image forming apparatus. The image forming apparatus according to claim 2.
The LED drive control means includes
When performing exposure at a second resolution of 1 / n (n is an even number) of the first resolution,
Storage means for holding image data at the time of the first LED driving;
Reading the image data in the storage means and driving the LED element during the second and subsequent LED driving;
An image forming apparatus.

Images