JP2766431B2 - Optical writing device for electrophotographic printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing device for an electrophotographic printer.

[0002]

2. Description of the Related Art Electrophotographic printers such as laser printers, light emitting diode printers, and liquid crystal printers have been known as image forming apparatuses. In particular, a light emitting diode printer can form a printer head only with an LED array chip and a rod lens array in which a plurality of light emitting diodes (hereinafter, referred to as “LED elements”) are linearly arranged. It is noted that the alignment is easy.

FIG. 2 is a schematic view of a main part of an electrophotographic printer having an LED array head. In the figure, a print data output unit 11 scans an appropriate subject such as a document with, for example, an image sensor (not shown), converts the read subject information into serial print data for each pixel, and sends the read information to the LED drive circuit 12 in the form of a video signal. Output in time sequence. The LED drive circuit 12 performs serial-parallel conversion of print data, outputs the print data to the LED array light source unit 14, and controls light emission of each LED element. Note that L
The ED array light source unit 14 usually forms a single LED array chip (or module) by monolithically integrating about 64 to 128 LED elements as light emitting elements having the same operating characteristics. Then, a plurality of the LED array chips are linearly arranged to form a printer head.

The light emitted from the LED element irradiates a photosensitive medium, for example, the surface of a photosensitive drum 19 through a converging rod lens array 16. The photosensitive drum 19 rotates in the direction of the arrow in the figure, is charged by the charger 18, and receives light from the rod lens array 16 to form an electrostatic latent image. The electrostatic latent image is sent to the developing unit 20 by the rotation of the photosensitive drum 19, is developed as a black and white binary image by toner, and is transferred to a predetermined sheet 23 by the transfer unit 22.

The LED array light source unit 14 used here
Actually, the exposure amount of the LED element, that is, the light emission intensity varies from one production lot to another due to differences in various conditions at the time of production. What is particularly important in this electrophotographic printer is the emission intensity of the LED elements of the LED array light source unit 14 that irradiates the photosensitive drum 19 with light. As described above, when the light emission intensity varies, unevenness in density occurs in the binarized printing, thereby deteriorating the printing quality.

FIG. 3 is a diagram showing the relationship between the drive current and the light emission intensity for each LED element. In the figure, the horizontal axis represents the driving current I of the LED element, and the vertical axis represents the light emission intensity P. Each LED
The average value of the light emission intensity _Pn of the device, that is, the average light emission intensity is expressed as P
_{When ave} , the maximum light emission intensity is P _max , and the minimum light emission intensity is P _min , variation of ΔP occurs at the maximum.

As described above, not only does the emission intensity _Pn of each LED element of the LED array light source section 14 (FIG. 2) vary, but also a maximum of ± 20% between each LED array chip arranged in the main scanning direction. A degree of variation had occurred.
Further, recently, an electrophotographic printer having a printing function corresponding to an image image such as photographic data and graphic data or colorization is required. In this case, an LED array head is provided with a gradation reproducing function. A printing method is provided.

Next, an LED array head control circuit used in the electrophotographic printer having the gradation reproducing function will be described. FIG. 4 shows L in a conventional electrophotographic printer.
FIG. 3 is a diagram illustrating an ED array head control circuit. In the figure, a print data output unit 11 includes a scanning type or fixed type image sensor 31 for reading subject information of a subject such as a document as analog density information, and a plurality of pieces of the analog density information for each pixel corresponding to one dot. A / D converter 32 for converting the pixel density data into 6-bit pixel density data, for example, and a pixel density data memory 33 for sequentially storing the pixel density data digitized by the A / D converter 32
It is composed of The pixel density data stored in the pixel density data memory 33 is output to the LED driving IC driver 41 as appropriate.

The LED driver IC driver 41 includes a register section 35 for storing pixel density data corresponding to each pixel in pixel units, and a D / A conversion section 36 for converting the pixel density data of the register section 35 into analog data. , The D / A converter 36
And a driver circuit 38 for supplying a driving current I corresponding to each amplified output to each LED element of the LED array light source section 14 (FIG. 2). It is formed by a resistor array (not shown).

When performing gradation printing with the electrophotographic printer having the above-described configuration, first, subject information of a subject such as a document is read as analog density information by an image sensor 31, and the analog density information is transmitted to an A / D converter 32. Output. The A / D converter 32 converts each pixel corresponding to one dot into pixel density data of a plurality of bits, for example, 6 bits, and sequentially stores them in the pixel density data memory 33.

Next, m consecutive pixel density data equal to the number of LED elements (here, m) provided in each LED array chip 40 are sequentially read out from the pixel density data memory 33 and read out. The data is supplied to the driving IC driver 41, and these are stored in the register section 35 and output simultaneously. The m pieces of pixel density data output simultaneously from the register section 35 are first output to a D / A conversion section 36, and the D / A conversion section 36 outputs analog data having a size corresponding to the density of each pixel. It is converted to a voltage value. Each output of the D / A conversion unit 36 is amplified by an amplifier circuit unit 37, and output to a driver circuit 38 as an output suitable for each LED element. As a result, in each LED element of each LED array chip 40, each output of the amplifier circuit section 37 is applied between the anode and the cathode and driven, and each resistance value of the driver circuit 38 (all the same value)
A drive current I determined by the current flows.

As described above, by increasing or decreasing the drive current I supplied to each LED element according to each output of the D / A converter 36, it is possible to make the light emission intensity _Pn of the LED element strong or weak. Becomes Therefore, the photosensitive drum 1
The density of pixels on 9 or any other photosensitive medium can be obtained in 64 steps. However, since the light emission intensity _Pn of the LED element with respect to the drive current I supplied to the LED element varies as described above, the drive current I supplied to each LED element is increased or decreased to reduce the light emission intensity _Pn . In the case of performing gradation printing in which the intensity is changed, even when the driving current I having the same value is supplied, the light emission intensity _Pn is different, so that the printing becomes uneven in density and the gradation reproduction is deteriorated.

Therefore, various correction methods for equalizing the exposure amount on the photosensitive drum 19 have been provided. An example will be described below. A light emission time control method for each LED element used as a correction method for equalizing the exposure amount on the photosensitive drum 19 can be expressed by the following equation (1). E = P _n × T (1) In the equation (1), E is the exposure amount to the photosensitive drum 19, P _n is the light emission intensity of the LED element, and T is the LED light emission time set for the LED element. is there. From equation (1), the exposure amount E is determined by the emission intensity _Pn of the LED element and the LED emission time T
Therefore, if the light emission intensity _Pn of the LED element is measured in advance with the exposure amount E being constant,
The LED emission time T can be set for each LED element, and the exposure amount E can be made uniform.

As described above, in order to set the LED emission time T for each LED element and drive the LED elements, an LED array drive circuit with a light emission intensity correction circuit is required. FIG. 5 is a diagram showing another example of an LED array head control circuit in a conventional electrophotographic printer. In the figure, 40 is an LED array chip composed of a plurality of LED array elements, 41 is an LED driver IC driver, and 42 is L
A correction memory for digitally approximating and storing an LED light emission time T for each ED element; 43, correction data; 44, a first clock; 45, a first register;
47 is a first latch signal, 48 is print data, 49 is a second latch signal.
A clock, 50 is a second register, 51 is a second latch signal, 52 is a latch circuit, 53 is a counter, 54 is a comparator circuit, 55 is an AND gate circuit, and 38 is a driver circuit.

Next, the operation of the above-configured LED array head control circuit will be described. First, correction data 43 of the LED emission time T for each LED element is output from the correction memory 42 to the first register 45 of the LED driving IC driver 41 in synchronization with the first clock 44. The first register 45 is a serial input-parallel output shift register which is cascaded, and its output is input to the first register 45 of the adjacent next-stage LED driver IC driver 41.

When the correction data 43 for 11 lines is obtained by the same operation, each LED driving IC driver 41
The output of the first register 45 is stored in the register group 46 of each stage as a correction number 1 (= 1 gradation) per LED element by the first latch signal 47. Hereinafter, the same operation is repeated, and the maximum number of corrections per LED element is 64.
The values up to (= 64 gradations) are stored in the register group 46.

As described above, when the correction data 43, which is the LED emission time T for each LED element, is stored in the register group 46 of the LED driver IC driver 41, the print data 4
8 is input to the second register 50 in synchronization with the second clock 49. The second register 50 is a serial input-parallel output shift register similar to the first register 45, and is cascaded, and its output is the second register of the adjacent next-stage LED driving IC driver 41. 50 is input.

When the print data 48 for one line is prepared by the same operation, the output of the second register 50 is input to the latch circuit 52 by the second latch signal 51. At this time, the counter 53 operates as a hexadecimal counter, and the output of the counter 53 is input to the comparator circuit 54 together with the output of the register group 46. The comparator circuit 54
Is the correction number as the output of the register group 46 and the counter 5
This is a circuit that matches the count value of 3, and outputs the LED emission time T per dot to the AND gate circuit 55, with the correction number other than the correction number being “0”.

On the other hand, the print data 48 of the latch circuit 52 is also input to the AND gate circuit 55. The AND gate circuit 55 includes a latch circuit 52 together with a comparator circuit 54.
An AND gate is formed for each LED element, and an LED emission time T that is valid only while the output of the comparator circuit 54 is digitally “1” is output to the driver circuit 38. The driver circuit 38 includes the AND gate circuit 5
5 only works while the output is digitally "1",
Each LED element of the LED array chip 40 emits light. Therefore, uniform printing can be performed.

[0020]

However, in the above-described conventional optical writing apparatus for an electrophotographic printer, it is necessary to incorporate a complicated circuit into the LED driver IC driver 41, and a general-purpose IC is required. The area of the IC driver chip becomes larger than that of the driver chip. Further, the manufacturing process of the LED driving IC driver 41 becomes complicated, so that the cost increases.

The present invention solves the above-mentioned problems of the conventional optical writing apparatus for an electrophotographic printer, and prevents unevenness in light and shade and deterioration in gradation reproduction due to variations in the emission intensity of LED elements, and reduces the variations. It is an object of the present invention to provide a low-cost optical writing apparatus for an electrophotographic printer which does not require a correction circuit for performing the operation.

[0022]

For this purpose, in an optical writing apparatus for an electrophotographic printer according to the present invention, a light emitting element formed by linearly arranging a plurality of light emitting elements which emit light corresponding to print data. An array, a photosensitive drum arranged opposite to the light emitting element array, and a plurality of liquid crystals arranged between the light emitting element array and the photosensitive drum and formed in an array corresponding to each light emitting element. A liquid crystal microlens array that includes a microlens and receives and focuses light emitted by the light emitting element, and irradiates the focused light to the photoconductor drum.

Further, a correction memory for storing correction data for correcting a variation in light emission intensity of each light emitting element is provided, and a liquid crystal microlens driving section generates a voltage corresponding to the correction data, and Is applied. The liquid crystal microlens changes the distribution of the refractive index according to the applied voltage. Further, a print data output unit for outputting pixel density data for each pixel may be provided, and a voltage corresponding to the pixel density data may be generated in the liquid crystal microlens driving unit and applied to the liquid crystal microlens.

[0024]

According to the present invention, a light emitting element array formed by linearly arranging a plurality of light emitting elements corresponding to print data as described above, and a light emitting element array disposed opposite to the light emitting element array are provided. And a plurality of liquid crystal microlenses arranged between the light emitting element array and the photosensitive drum and formed in an array corresponding to each light emitting element. When the light emitting element emits light corresponding to the print data, the light emitted by the light emitting element is focused by the liquid crystal microlens,
An image is formed on the photosensitive drum.

Further, a correction memory for storing correction data for correcting the variation of the light emission intensity of each light emitting element is provided, and the liquid crystal microlens driving section generates a voltage corresponding to the correction data for each light emitting element. Then, the voltage is applied to the liquid crystal microlens. The liquid crystal microlens changes the refractive index distribution according to the applied voltage, and changes the focal length.

Accordingly, since the intensity of the light image on the photosensitive drum changes as the focal length changes, it is possible to correct the variation in the light emission intensity of the light emitting elements. Also,
When gradation printing is performed by providing a print data output unit that outputs pixel density data for each pixel, a voltage corresponding to the pixel density data is generated in a liquid crystal microlens driving unit and applied to the liquid crystal microlens. Then, dots of different sizes are formed as electrostatic latent images on the photosensitive drum, and gradation can be expressed by the size of the print dots.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic view of an optical writing device of an electrophotographic printer according to a first embodiment of the present invention. In the figure, light L due to light emission of the LED array chip 40 is shown.
Is converted into linearly polarized light by the polarizer 61, then forms an image on the photosensitive drum 19 through the liquid crystal microlens array 62 to form an electrostatic latent image. The liquid crystal microlens array 62 is formed by forming the same number of liquid crystal microlenses 64 as the LED elements 63 of the LED array chip 40 in an array.
And are disposed so as to correspond to each other.

The print data output section 11 has a so-called scanning type or fixed type image sensor 31 (see FIG. 4) for reading subject information of a subject such as a document. The subject information of the subject is converted into serial print data 48 for each pixel, and is output to the LED drive circuit 12 in the form of a video signal in time sequence. The LED drive circuit 12 controls the light emission of each LED element 63 by performing serial-parallel conversion of the print data 48 and sending the print data 48 to the LED array light source unit 14.

On the other hand, the correction memory 42 includes the LED element 6
The correction data 43 of the variation of the light emission intensity _Pn of No. 3 is stored in advance in a digital amount, and the correction data 43 is supplied to the liquid crystal microlens driving unit 68. The liquid crystal microlens driving section 68 performs D / A conversion of the correction data 43 by the D / A conversion section 71 and amplifies the output to an output suitable for driving the liquid crystal microlens 64 by the amplifier circuit section 72. In order to prevent the deterioration of the
To convert to AC voltage.

FIG. 6 is an explanatory diagram of a liquid crystal microlens array according to the first embodiment of the present invention. (A) of the figure is 1
Sectional view of the liquid crystal microlens array 62 for pixels,
(B) is a plan view of the liquid crystal microlens array 62 for one pixel. In the figure, 61 is a polarizer, 62, 6
2 _n , 62 _{n + 1} and 62 _n-1 are liquid crystal microlenses.
The upper glass substrate 75 and the lower glass substrate 76 are formed with electrodes 77 and 78 (the material is preferably a material having a light blocking property such as chromium, for example), and circular holes 79 and 80 are formed vertically. It is formed concentrically by a technique such as photolithographic etching.

The electrodes 77 are connected to the liquid crystal microlens driving section 68 (FIG. 1), and each LED element 63
, A potential corresponding to the correction data 43 for correcting the variation of the light emission intensity _Pn is formed, while the electrode 78 has a common potential for all the pixels. The upper and lower glass substrates 75 and 76 are coated with an alignment material (not shown) such as polyimide on the surfaces of the electrodes 77 and 78, and subjected to an appropriate parallel alignment process such as rubbing, and then are appropriately formed using a spacer or the like (not shown). They are opposed and supported at an appropriate interval, for example, 50 [μm] (hereinafter referred to as “cell thickness”). A p-type nematic liquid crystal 82 is sealed between the upper and lower glass substrates 75 and 76, and the periphery is sealed with a sealing material (not shown). The transmission axis of the polarizer 61 is set to be the same as the direction of the rubbing process.

FIG. 7 is a view showing the orientation direction of liquid crystal molecules in the first embodiment of the present invention. In the figure, 75 is an upper glass substrate, 76 is a lower glass substrate, 77 and 78 are electrodes, 79 and 80 are circular holes, 82 is a p-type nematic liquid crystal, and 83 is an electrode 77 of the upper and lower glass substrates 75 and 76. , 78, an AC power supply for forming an AC electric field
Reference numeral 4 denotes liquid crystal molecules of the p-type nematic liquid crystal 82.

As shown in the figure, when an appropriate AC electric field is formed between the electrodes 77 and 78, the orientation of the liquid crystal molecules 84 changes. The refractive index of the light L (FIG. 1) is
It increases continuously toward the central axis of 9,80. FIG.
FIG. 3 is a refractive index distribution characteristic diagram of the liquid crystal microlens according to the first embodiment of the present invention.

In this case, electrodes 77 and 78 having circular holes 79 and 80 (FIG. 7) having a diameter of 0.7 [mm] are used, and holes 79 and 80 when the cell thickness is 50 [μm]. 3 shows the distribution of the refractive index n in the radial direction. When the voltage applied between the electrodes 77 and 78 is sufficiently small,
Since the orientation direction of the liquid crystal molecules 84 does not change, the distribution of the refractive index n is uniform.
Changes the orientation direction. Accordingly, the refractive index n is obtained continuously changing distribution in the radial direction, the distribution of the refractive index n is _{n = n 0 (1-A} · r 2/2) ... (2) n: refractive index n _0: Refractive index at center A: Refractive index distribution constant r: Distance from center Approximately, and has optical characteristics equivalent to a rod lens or a convex lens. Further, the focal length f can be represented by f = {A ^1/2 · n ₀ · sin (A ^1/2 · d)} ⁻¹ (3) d: cell thickness The minimum value of the focal length f is f = 2d / πn ₀ (4), and is obtained when A = π ² / 4d ² (5).

From FIG. 8, increasing the voltage v _f to be applied becomes small refractive index n ₀ of the center, the refractive index distribution constant A is decreased, the change in the refractive index n is found to be moderate. Further, when the focal length f is set to the conditions of equation (5) so as to minimize the refractive index with an increase of the voltage v _f n
_{Both 0} and the refractive index distribution constant A decrease, and from equation (3), the focal length f increases.

FIG. 9 shows the relationship between the voltage applied to the liquid crystal microlens.
FIG. 4 is a diagram illustrating a relationship between applied voltage and optical parameters. Figure smell
And the refractive index n at the center when the voltage is increased₀,refraction
Rate dispersion constant A ^1/2Liquid crystal microlenses 64 due to changes in
The change of the optical parameter in FIG. 1 is shown in the direction of the arrow.
However, here, the liquid crystal microlenses 64 are generally
Lens performance equivalent to rod lenses for electrophotographic printers
The change of the optical parameter when having the is shown.

FIG. 10 is an explanatory diagram of the correction of the light emission intensity in the first embodiment of the present invention. In the figure, 12 is LE
D drive circuit, 19 is a photosensitive drum, 40 is an LED array chip, 61 is a polarizer, 62 is a liquid crystal microlens array, and 63 is an LED element. When the liquid crystal microlens 64 (FIG. 1) is used in place of the rod lens, the intensity E (x) of the light image becomes spheroidal, where x is the distance from the center O formed on the photosensitive drum 19. It can be represented by a body. Here, in the case of the LED printer, since line scanning is performed, it can be considered as an intensity distribution on a plane passing through the center O on the photosensitive drum 19. _{Therefore, E (x) = E 0} · {1- (x / x 0) 2} 1/2 E 0: intensity of the light image of the center x _0: expressed in field radius. Therefore, the intensity E (x) of the light image on the photosensitive drum 19 is proportional to the intensity E ₀ of the light image at the center O. Further, since the intensity E ₀ of the light image at the center O is proportional to the light emission intensity P _n of the LED element 63 as the light source and is proportional to (n ₀ · A ^1/2 ) ² , the condition of the equation (4) is satisfied. As the voltage is increased from the minimum voltage v _min to be satisfied, the intensity E ₀ of the optical image at the center O decreases. Here, _assuming that the light emission intensity _Pn of the LED element 63 varies ± 20% from the average light emission intensity P _ave , P _min = 0.8 P _ave P _max = 1.2 P _ave .

Therefore, the liquid crystal microlens 64 corresponding to the LED element 63 having the minimum light emission intensity _Pmin is set to the minimum voltage v.
Drive with _min . At this time, the lens constant K = (n ₀ · A
^1/2 ) ² is the maximum value _Kmax . Also, the maximum emission intensity P
_max (in this case, the emission intensity P _n is the strongest) liquid crystal microlenses 64 corresponding to the drives at the minimum voltage v _min higher _{voltage, K min = K max · P} min / P max = (2/3) · The maximum voltage _vmax is set so as to be _Kmax . Then, the lens constants K _n of the liquid crystal microlens 64 in accordance with the emission intensity P _n of the respective LED elements 63, by applying a voltage v _n such that the _{K n = K max · P min} / P n photosensitive The intensity E (x) of the light image on the body drum 19 is made uniform.

As described above, the liquid crystal microlenses 64
Refractive index n due to electro-optic effect of liquid crystal ₀Convex by the distribution of
It shows the lens effect and the applied voltage v_fLarge
Refractive index n by small₀Change the focal length f
Which lens constant K_nCan be changed. Accordingly
And the applied voltage v_fDrum 1 depending on the size of
9 and the intensity E of the light image at the center O₀Change
Can be

The liquid crystal microlenses 64 corresponding to the strongly emitting LED elements 63 increase the focal length f,
The intensity E ₀ of the optical image at the center O on the photosensitive drum 19 can be reduced. In addition, the LED element 63 that emits light weakly
The liquid crystal micro lens 64 corresponding to the photosensitive drum 1
By forming an image on the photosensitive drum 9, dots can be reduced, and the intensity E ₀ of the optical image at the center O of the photosensitive drum 19 can be increased.

Correction data 43 for variations in light emission intensity _Pn
FIG. 1 shows that a voltage v _n for driving each liquid crystal microlens 64 is _converted into an appropriate plurality of bits, for example, 6-bit data by A.
The result of the / D conversion is stored in the correction memory 42. When operating as an electrophotographic printer,
The 6-bit correction data 43 stored in the correction memory 42 is supplied to the D / A converter 71, and is converted into an analog voltage value corresponding to each correction data 43. Each output of the D / A conversion section 71 is amplified by the amplifier circuit section 72, and the liquid crystal microlens 64 corresponding to the LED element 63 that emits the strongest light corresponds to the LED element 63 that emits the weakest light at the maximum voltage _vmax. If the liquid crystal microlens 64 is set to be driven at the minimum voltage _vmin , the intensity E (x) of the light image on the photosensitive drum 19 can be made uniform.

In the above embodiment, the holes 79 and 80 of the liquid crystal microlens 64 are for generating a non-uniform alternating electric field to change the distribution of the refractive index n to obtain the convex lens effect. Therefore, the shape and size can be changed as long as each LED element 63 has a one-to-one correspondence. Further, the cell thickness d of the liquid crystal microlens 64 is appropriately determined by the shape and size of the holes 79 and 80 and the material properties of the liquid crystal material, and is not limited.

Further, the print data is set to two gradations of black and white,
While controlling the light emission intensity P _n of the LED elements 63, typically because the emission intensity P _n of the LED element 63 as shown in FIG. 3 has a linearity, at the same time increases or decreases the driving current I of all the LED elements 63 Even when the density of the pixel is changed by, for example, changing the light emission intensity _Pn of each LED element 63, the variation is constant without being affected by the drive current I. Therefore, there is no need to change the correction data 43. Therefore,
The print data 48 is not limited to two gradations, and may be a gradation print by controlling the drive current I (in this case, the print data 4
The present invention can be applied also to the case where 8 is a plurality of bits.

FIG. 11 is a schematic view of an optical writing device of an electrophotographic printer according to a second embodiment of the present invention, and FIG. 12 is a detailed view of a main part of FIG. In the figure, the LED array chip 4
The light L by the light emission of 0 is converted into linearly polarized light by the polarizer 61 and then imaged on the photosensitive drum 19 by the liquid crystal microlens array 62 to form an electrostatic latent image. The liquid crystal microlens array 62 is provided with the L of the LED array chip 40.
The same number of liquid crystal microlenses 64 as the ED elements 63 are formed in an array.
Are arranged so as to face the LED elements 63 in a one-to-one correspondence.

The print data output unit 11 includes a scanning or fixed image sensor 31 for reading subject information of a subject such as a document, and converts the subject information read by the image sensor 31, that is, analog density information into one dot. A / D converter 32 for converting pixel density data of a plurality of bits, for example, 6 bits, for each corresponding pixel, and pixel density data memory 33 for sequentially storing pixel density data
It is composed of The pixel density data stored in the pixel density data memory 33 is appropriately supplied to the liquid crystal microlens driving unit 68 and the OR circuit unit 86.

The liquid crystal microlens driving section 68 includes a register section 35 for storing each pixel density data in pixel units.
And a D / A conversion unit 36 for converting the pixel density data of the register unit 35 into an analog signal, and an amplification circuit unit 37 for amplifying the output of the D / A conversion unit 36. The OR circuit section 8
Numeral 6 is a 6-bit OR circuit for pixel density data of a plurality of bits, for example, 6 bits, performs an OR operation between each bit, and converts the pixel density data into only binary values of "0" or "1". .

That is, the output of the OR circuit unit 86 becomes “0” when white (pixel density data = 000000), and becomes “1” otherwise, and is output to the LED drive circuit 12. . The LED drive circuit 12 is connected to the OR
The output of the circuit unit 86 is converted from serial to parallel and output to the LED array chip 40 to control the light emission of each LED element 63. Here, when the output of the OR circuit unit 86 is “0”, the LED element 63 is extinguished, and when the output of the OR circuit unit 86 is “1”, the L1D element 63 emits light.

The liquid crystal microlens array 62 is
The voltage v applied as in the first embodiment. _nThe LED element 63
And the intensity E (x) of the light image on the photosensitive drum 19
Can be changed to perform gradation printing. FIG. 13 shows the present invention.
FIG. 9 is an explanatory diagram of gradation printing in the second embodiment. In the figure
Here, 12 is an LED drive circuit, 19 is a photosensitive drum,
40 is an LED array chip, 61 is a polarizer, 63 is LE
D element. The amount of light L from the LED element 63 is constant
Value P₀And the dot area on the photosensitive drum 19 is
If S, the light intensity W per unit area is W = P₀/ S. However, the liquid crystal micro lens 64
Light loss, such as in FIG.
There is no such thing.

In the figure, _Ra represents an applied voltage v _a, and LE
This shows the image forming state of the photosensitive drum 19 when the light L from the D element 63 is most focused, and the dot is the smallest (the dot area on the photosensitive drum 19 is _Sa ) in one pixel. At this time, the light intensity W _a per unit area
Is _{W a = P 0 / S a} , the maximum value.

As the applied voltage increases, the focal length f increases, and the dot area S formed on the photosensitive drum 19 increases. R _b represents the applied voltage as v _b (>
v _a) and to the dot area on the maximum dots (photosensitive drum 19 in the ,, one pixel shows the imaging state of the photoreceptor drum 19 if is S _b). Light intensity W _b per unit area at this time is _{W b = P 0 / S b} , the minimum value.

FIG. 14 is a light sensitivity characteristic diagram of the photosensitive drum according to the second embodiment of the present invention. The figure shows the photosensitive drum 1
9 shows the relationship between the light intensity W per unit area and the light sensitivity k of the photosensitive drum 19 in FIG. 9 (FIG. 11). Therefore, by setting the light intensity W _a in the saturation region of the optical sensitivity k of the photosensitive drum 19 shown in FIG., The light intensity W _a, photosensitivity k of the photosensitive drum 19 with respect to W _b are equal.

Accordingly, the photosensitive drum 19 is
The potential of the electrostatic latent image is_a, R_bIs equal to
The print density of the dots is equal. Therefore, per pixel
It is possible to reproduce the shading of printing only with the dot area S
Become. That is, the imaging state R _aIn the case of, the dot area S is
Since it is minimum, the print density per pixel is the lowest.
Also, state R_bIn the case of, since the dot area S becomes the maximum,
The print density per pixel is the highest.

Here, the subject information of the subject such as a document is converted into a plurality of bits, for example, 6 bits, of digitally displayed pixel density data for each pixel corresponding to one dot in the print data output section 11 and the liquid crystal microlens is obtained. It is output to the drive unit 68. In the liquid crystal microlens driving section 68, the pixel density data is stored in the register section 35.
The signal is input to the D / A converter 36 via FIG. 12 and is converted into an analog voltage value corresponding to the pixel density data. The output of the D / A converter 36 is amplified by an amplifier circuit 37,
The voltage v _a to print the lightest pixel, by setting the voltage v _b to the darkest printing, the photosensitive drum 1
In step 9, 64 levels of pixel density can be obtained.

Further, even when the light emission intensity _Pn of the LED element 63 varies, as is apparent from FIG.
If the light intensity W per unit area is changed within the saturation region of the photosensitivity k of the photosensitive drum 19, the potential of the electrostatic latent image is not affected, and the density of the dot pixels does not change. Therefore, even if the emission intensity _Pn of the LED element 63 varies, the characteristics of gradation printing do not deteriorate. In the above-described embodiment, 6-bit pixel density data is used, but data of a plurality of other bits may be used.

It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0056]

As described above in detail, according to the present invention, a light emitting element array formed by linearly arranging a plurality of light emitting elements emitting light corresponding to print data, and the light emitting element array And a plurality of liquid crystal microlenses disposed between the light emitting element array and the photosensitive drum and arranged in an array corresponding to each light emitting element.

There is provided a correction memory for storing correction data for correcting a variation in light emission intensity of each light emitting element.
The liquid crystal microlens driving unit generates a voltage corresponding to the correction data for each light emitting element and applies the voltage to the liquid crystal microlens. The liquid crystal microlens changes the distribution of the refractive index according to the applied voltage, and changes the focal length.

Since the intensity of the light image on the photosensitive drum changes as the focal length changes, it is possible to correct the variation in the light emission intensity of the light emitting element. Therefore, it is not necessary to select the light emitting elements when manufacturing the light emitting element array, and the cost can be reduced. Further, since there is no need to incorporate a complicated circuit for correction into the light emitting element driving IC driver chip, the light emitting element driving IC
Not only can the manufacturing process of the driver chip be simplified, but also the cost can be reduced.

In the case where a print data output section for outputting pixel density data for each pixel is provided to perform gradation printing, a voltage corresponding to the pixel density data is generated in a liquid crystal microlens driving section, and the liquid crystal microlens is generated. Is applied. In this case, gradation printing is performed by changing the size of the light image on the photosensitive drum and changing the print dot area per pixel, so that even if the light emission intensity of the light emitting element varies, the pixel density Gradation printing can be performed without affecting the print quality, and the print quality can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical writing device of an electrophotographic printer according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a main part of an electrophotographic printer including an LED array head.

FIG. 3 is a diagram illustrating a relationship between a drive current and an emission intensity for each LED element.

FIG. 4 is a diagram showing an LED array head control circuit in a conventional electrophotographic printer.

FIG. 5 is a diagram showing another example of an LED array head control circuit in a conventional electrophotographic printer.

FIG. 6 is an explanatory diagram of a liquid crystal microlens array according to the first embodiment of the present invention.

FIG. 7 is a diagram showing an alignment direction of liquid crystal molecules in the first embodiment of the present invention.

FIG. 8 is a refractive index distribution characteristic diagram of the liquid crystal microlens in the first embodiment of the present invention.

FIG. 9 is a diagram illustrating a relationship between a voltage applied to a liquid crystal microlens and an optical parameter.

FIG. 10 is an explanatory diagram of correction of light emission intensity in the first embodiment of the present invention.

FIG. 11 is a schematic diagram of an optical writing device of an electrophotographic printer according to a second embodiment of the present invention.

FIG. 12 is a detailed view of a main part of FIG. 11;

FIG. 13 is an explanatory diagram of gradation printing in a second embodiment of the present invention.

FIG. 14 is a light sensitivity characteristic diagram of the photosensitive drum according to the second embodiment of the present invention.

[Explanation of symbols]

 11 Print Data Output Unit 19 Photoconductor Drum 40 LED Array Chip 43 Correction Data 42 Correction Memory 48 Print Data 62 Liquid Crystal Micro Lens Array 63 LED Element 64 Liquid Crystal Micro Lens 68 Liquid Crystal Micro Lens Drive L Light n Refractive Index

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 1/036 (72) Inventor Kazuo Tokura 1-7-12 Toranomon, Minato-ku, Tokyo Inside Oki Electric Industry Co., Ltd. (72) Inventor Yukio Nakamura 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP-A-2-96782 (JP, A) JP-A-4-201270 (JP, A) JP-A-2-238425 (JP, A) JP-A-4-196869 (JP, A) JP-A-5-80271 (JP, A) JP-A-5-2318 (JP, A) (58) Fields investigated ( Int.Cl. ⁶ , DB name) B41J 2/44 B41J 2/445 B41J 2/45 B41J 2/455 H04N 1/036

Claims (2)

(57) [Claims] 1. A light emitting element array formed by arranging a plurality of light emitting elements that emit light corresponding to print data on a straight line, and (b) a light emitting element array disposed opposite to the light emitting element array. A photosensitive drum; and (c) a plurality of liquid crystal microlenses disposed between the light emitting element array and the photosensitive drum and formed in an array corresponding to each light emitting element. Receiving and converging, a liquid crystal microlens array for irradiating the condensed light to the photosensitive drum,
(D) a correction memory storing correction data for correcting the variation of the light emission intensity of each light emitting element; and (e) a liquid crystal microlens drive for generating a voltage corresponding to the correction data and applying the voltage to the liquid crystal microlens. (F)
An optical writing device for an electrophotographic printer, characterized in that the liquid crystal microlens has means for changing a distribution of a refractive index in accordance with an applied voltage. 2. A light-emitting element array formed by arranging a plurality of light-emitting elements that emit light in accordance with print data on a straight line, and (b) a light-emitting element arranged to face the light-emitting element array. A photosensitive drum; and (c) a plurality of liquid crystal microlenses disposed between the light emitting element array and the photosensitive drum and formed in an array corresponding to each light emitting element. Receiving and converging, a liquid crystal microlens array for irradiating the condensed light to the photosensitive drum,
(D) a print data output unit that outputs pixel density data for each pixel, and (e) a liquid crystal microlens drive unit that generates a voltage corresponding to the pixel density data and applies the voltage to the liquid crystal microlens, f) The optical writing device for an electrophotographic printer, wherein the liquid crystal microlens has means for changing a distribution of a refractive index in accordance with an applied voltage.