JPS63319167A - Method and apparatus for driving light emitting element array - Google Patents

Abstract

PURPOSE:To obtain excellent gradation printing without decreasing resolution by converting the density value of an object to be printed of each pixel into that of displaying a plurality of bits, converting them into current values corresponding to the number of the pixels, and driving light emitting elements corresponding to the pixels by light emitting powers corresponding to the current values. CONSTITUTION:Density values of m pieces of continuous pixels corresponding to the predetermined number of LED elements provided on one chip are sequentially read out, supplied to a density gradation circuit 58, stored in a register 62, and simultaneously output in parallel. The output density values of the m pieces of the pixels are simultaneously supplied to a current converter 64, supplied to a D/A converter 66, and converted to analog voltage values. The outputs of the converter 66 are amplified through an amplifier 66a, and supplied as voltage values adapted for the LEDs to a resistor array 68. Thus, the currents to the LEDs are increased or decreased in response to the output voltage values of the converter 66. As a result, the light emitting powers of the LEDs can be weakened and strengthened, thereby obtaining the densities of printing pixels to a recording medium with at least 65 gradations.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for driving a light emitting element array suitable for use as a light source of an optical printer or other image recording apparatus.

(Conventional technology) Conventionally, laser printers, light emitting diode printers,
The development and commercialization of electrophotographic printers such as liquid crystal printers are progressing (for example, Japanese Patent Application Laid-Open No. 60-24106
No. 8, [Nikkei Electronics 41985 No. 4-8 (
No. 366) pp. 135-157). Among these, light-emitting diode printers have a small and simple structure consisting of a printer head, an LED array chip in which a large number of light-emitting diodes (hereinafter referred to as LEDs) are arranged in a straight line, and a focusing aperture and a lens array. and, moreover,
It is attracting attention because the alignment of the optical system is easy.

FIG. 4 is a diagram schematically showing the configuration of the main parts of a conventionally proposed optical printer using an LED array in an optical head. In this configuration, numeral 10 denotes a print data reading section which reads object information by scanning a suitable object, such as a document, using any suitable reading means (e.g., an image sensor). The signal is then supplied to the LED driver 12, where it undergoes serial-to-lateral conversion and is converted into an ED array light source 14.
to cause each LED to emit or extinguish %. In addition, LE
The D-array light source section 14 is usually formed by integrating approximately 64 to 128 LEDs with the same operating characteristics as light emitting elements into one chip (or module), and arranging the required number of chips in a straight line. It is composed of The emitted light of the LED is focused on the focusing rod lens array 1.
After step 6, the recording medium, for example, is rotated in the direction of the arrow in the figure, and the surface of the photosensitive drum charged by the charger 20 is irradiated to form an electrostatic latent image. The electrostatic latent image is sent to a developing device 22 by one rotation of the photosensitive drum, where it is developed as a black and white binary image using toner, and transferred onto a desired paper 26 by a transfer device 24.

In this way, for example, print data such as characters and figures can be converted into black and white.
When printing only values, an LED driving section 12 as shown in FIG. 5 is used. In the same figure, 30a to 3
0n is a serial-parallel (S/P) conversion shift register, 32a to 32n are gate circuits, 34a to 34n are driver circuits, and 36a to 36n are LED array chips. The video image signals for each pixel are transferred to shift registers 30a to 30n.
Each LE of each LED array 36a to 36n
The pixel data corresponds to D. This pixel data is supplied from the input terminal 40, and is input to the gate circuits 32a to 32n together with a strobe signal that controls the light emission time of the LED, from which it is output for a certain period of time as the light emission or extinction state of the LED.

This output is the driver circuit 34a to 34 corresponding to the LED.
n. Conventionally, a constant voltage Voo is applied to the driver circuits 34a to 34n from the voltage terminal 42, so that each ED in the light emitting state receives the constant voltage VoD.
A current of the same value is supplied by all of them, and the luminance of light emission is also the same.

(Problem to be Solved by the Invention) Recently, however, printers have been developed for practical use that have a printing function that can handle images such as photographic data and graphic data, as well as color printing. In that case, instead of the above-mentioned binary printing method,
It is desired that the light emitting section of an optical head has a gradation function. As a method for this, a printing method has conventionally been proposed in which a pixel signal having a multi-value function is added to the video image signal to provide gradation. This gradation method includes a dither method and an area gradation method, and when printing using LED,
The former method lowers the resolution per pixel, and the latter method requires an ultra-high density LED array, making it difficult to put it into practical use from a technical standpoint.

The first object of the invention of this application is to provide a method for driving a light emitting element array that is excellent in gradation printing without reducing the resolution or increasing the density of the LED array. There is a particular thing.

A second object of the invention of this application is to provide an apparatus for implementing the above-described method for driving a light emitting element array.

(Means for Solving the Problems) In order to achieve the object of the first invention, according to the method for driving a light emitting element array of the present invention, each light emitting element of the light emitting element array is driven based on subject information for each pixel. In order to emit light and record a subject image on a recording medium, the density value of the subject for each pixel is converted into a multi-bit density value, and the density value of each pixel is converted all at once or in a size corresponding to the required number of pixels. The current value is converted into a current value, and the light emitting element corresponding to each pixel is driven with the light emitting power corresponding to the respective current value.

In order to achieve the object of the second invention, according to the present invention, there is provided a light emitting element array for recording a subject image on a recording medium by causing each light emitting element of the light emitting element array to emit light based on subject information for each pixel. The driving device includes: a pixel density data memory that converts the density value of a subject for each pixel into a multi-bit density value and stores it; a register that reads density values of a plurality of pixels from the memory and stores them; The multiple concentration values accumulated in the
The present invention is characterized in that it includes a density gradation circuit provided with a current conversion unit that converts the current and outputs the converted current to a light emitting element corresponding to each pixel.

(Function) As described above, according to the method and device for driving a light emitting element array of the present invention, in order to control the light emitting power of the light emitting elements,
A configuration in which the object density is converted into density value information in a multi-bit display, for example, at least 6 bits, for each pixel, and these density values are converted into current values of corresponding magnitudes, and the current values are driven to flow through the corresponding light emitting elements. Therefore,
It is possible to record a subject image with at least 64 gradations per pixel, so even if the conventional dot density is maintained, the resolution per pixel is not reduced in terms of the gradation of print density.

Further, since the device of the present invention has a simple configuration including a pixel density data memory and a density gradation circuit provided with a register and a current converter, the manufacturing cost is low.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram for explaining an embodiment of a method and apparatus for driving a light emitting element array according to the present invention. In this example, the light emitting element is a light emitting diode (LED) of 1.2, .
--1m, and m of these LEDs make one chip (
One chip constitutes m dots), and multiple chips 60a
, 60b, . . . , 60n are arranged in a linear manner and driven in a time-division manner.

In the figure, 50 is a print data reading section, 52 is a normal scanning type or fixed image sensor (its configuration does not matter) for reading image information of an object such as a document, and 54 is an image sensor, for example. Reference numeral 52 is an A/D converter for converting the read analog density information of the object into a digitally displayed density value of a plurality of bits, for example, at least 6 bits or more, for each pixel corresponding to 1 dot=y.

For convenience of explanation, an example of 6-bit conversion will be described below. In this embodiment, the digitally displayed density values of each pixel converted in this way are sequentially stored in the pixel density data memory 56. In this case, the density values of all pixels may be stored once and then read out from this memory, or the density values of each of the required number of pixels may be stored and read out according to the design. Go one after another,
Alternatively, it may be configured to perform storage and reading in parallel, and which form is used is simply a matter of design.

Next, in this embodiment, the LEDs provided in one channel
The density values of m consecutive pixels corresponding to the required number of elements are sequentially read out and supplied to the density gradation circuit 58, stored in the register 62, and output in parallel simultaneously. Preferably, this reading is performed simultaneously for each chip. In this case, in order to output density value data with at least 6 bits (i.e. 64 gradations) per pixel, that is, LED (dot), in the case of m dots, 6
×m dots are output.

The density values for each of the m pixels simultaneously output from the register 62 are supplied to the current converter 64 at the same time. In this embodiment, the current converter 64 preferably includes a D/A converter 66 and a resistor array 68. The above-mentioned simultaneously inputted m density values are first supplied to the D/A converter 66, where they are converted into analog voltage values having relative magnitudes corresponding to the respective density values.

FIG. 2 is an explanatory diagram of an example of the linear conversion characteristics of this A/D converter 66, in which the horizontal axis plots the number of print density data corresponding to the digital density value expressed in 6 bits, and the vertical axis shows the number of print density data corresponding to the digital density value expressed in 6 bits. The output voltage (V) of the D/A converter is plotted and shown. This conversion characteristic is the least significant bit (LSB
) from the number of print density data “O” corresponding to the most significant bit (MSB) to the number of print density data “64” corresponding to the most significant bit (MSB), the change width is changed at equal intervals in 64 steps,
Therefore, the density value of the object corresponding to each pixel (dot) is linearly converted into a relative voltage value in one of 64 levels.

The output of this D/A converter 66 is supplied to a built-in amplifier circuit 66a, which is provided as required. The voltage is then amplified through the LED and supplied to the resistor array 68 to a voltage value suitable for each LED, that is, each dot.

In this embodiment, each chip 6 constituting the light emitting element array
Each LEDI~m forming m dots of 0a~60n
The anode side of each is connected to the corresponding output side of the D/A converter 66 via the individual resistors constituting the resistor array 68. The resistance values of these resistors are all set to the same value. on the other hand,
The cathode side of each LED is grounded through a common switching element for each chip. By configuring in this way, each switching element 70a, 70b, ---1? When ON is sequentially switched in a fixed time unit to make it conductive, the switching element that has become conductive, for example, the chip 6 connected to 70a.
A corresponding voltage from the D/A converter 66 described above is applied between the anode and cathode of each of the LEDs 0a to 0a to drive the LED, and a current of a magnitude determined by each resistor of the resistor array 68 is applied to each LED. flows.

In this way, it is possible to increase or decrease the current to each LED in accordance with the output voltage value of the D/A converter 66, and as a result, it is possible to vary the intensity of the light emitting power of the LEDs, and it is possible to increase or decrease the light emitting power of the LEDs. The print pixel density on the recording medium is at least 64
It can be obtained in stages of gradation.

In the embodiment described above, the switching elements 70a to 70n
Since the chips 60a to 60n are driven in a time-divided manner using ji#, manufacturing costs can be reduced and the light source section can be simplified.

FIG. 3 is a block diagram for explaining another embodiment of the method and drawing according to the present invention. In the figure, the same components as those shown in FIG. 1 are designated by the same reference numerals.

In this embodiment, density gradation circuits 58a to 58n are provided in parallel for each chip 60a to 60n, and these density gradation circuits 58a to 58n are driven all at once, so that all of the chips 60a to 60n are The LEDs I to m are driven to emit light at the same time. Therefore, unlike the embodiments described above, there is no need to provide a switching element for switching each chip. Note that these density gradation circuits 58
Since a to 58n have the same circuit configuration as the density gradation circuit 58 described above, a detailed explanation thereof will be omitted.
The digital density values for the LEDs 0a to 60n are sequentially read out, and the digital density values of each pixel corresponding to each chip 60n to 60a are stored in the respective registers 62n to 62n.
62a, and all registers 62a~
When the density data is taken into chip 62n, these density gradation circuits 58a to 58n are driven all at once, thereby driving each LED of all chips 60a to 60n to emit light. With such a simultaneous driving method, high speed and low power consumption can be expected. In addition, 64a-6
4n is a current converter, 66a to 66n are D/A converters including amplifier circuits, and 68a to 68n are resistor arrays.

It is clear that the invention is not limited to the embodiments described above. For example, in the embodiment described above, the density value of each pixel from the subject is converted into a digital density value of 6 bits in binary number, or the density value is converted using bits larger than 6 bits and a corresponding density gradation circuit is used. By doing this, it is possible to display a printed image with a greater number of gradation densities than 64 gradations. Further, depending on the case, conversion of 6 bits or less may be possible.

Furthermore, in the above-described embodiment, the density gradation circuit is configured with a register, a D/A converter, and a resistor array, but other structures may be used as long as they can convert each pixel into a current value corresponding to the subject density. It may be configured as follows.

(Effects of the Invention) As is clear from the above description, according to the light emitting element array driving method and device of the present invention, in any case, the object density can be set to at least 6 bits per pixel or more, that is, 64 or more bits per pixel. Digital conversion into gradation density information of Since the density has at least 64 gradations, the dot density that has been established in the past, for example, 240 to 600 DP
Even when the light emitting element array of I is used, there is no fear that the resolution will be reduced in terms of the gradation of print density per pixel.

Furthermore, since the device of the present invention has a simple configuration including a pixel density data memory, a register, and a density gradation circuit provided with a current converter, the manufacturing cost is low.

Since the present invention has the above-mentioned advantages, it is particularly suitable for application as a light source for an optical printer using a photoreceptor drum.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining an embodiment of a driving method and apparatus for a light emitting element array of the present invention, and FIG. 2 is an explanatory diagram of an example of linear conversion characteristics of an A/D converter used in the present invention. , FIG. 3 is a block diagram for explaining another embodiment of the method and apparatus of the present invention, and FIG. 4 schematically shows the configuration of the main parts of a conventionally proposed optical printer using an LED array in an optical head. Fig. 5 is a block diagram of an LED driving section used in a conventional optical printer. 50...Print data reading section, 52...Image sensor 54...A/D converter 56...Pixel density data memory 58.58a-58n...Density gradation circuit 60a-60
n... (light emitting element) chips 62.62a to 62n.
...Register 64...Current converter 66.66a - 66n -D/A converter 66a...
Amplifier circuits 68.68a to 68n...resistance array. 70a to 70n... switching elements.

Claims (2)

[Claims] (1) In a method of driving a light emitting element array for recording a subject image on a recording medium by causing each light emitting element of the light emitting element array to emit light based on subject information for each pixel, a plurality of density values of the subject for each pixel are set. Converts the density value of each pixel to a density value in bit display, converts the density value of each pixel to a current value of the corresponding size all at once or for the required number of pixels, and causes the light emitting element corresponding to each pixel to emit light corresponding to each current value. A method for driving a light emitting element array, characterized in that it is driven by power. (2) In a light-emitting element array driving device for recording a subject image on a recording medium by causing each light-emitting element of the light-emitting element array to emit light based on subject information for each pixel, a plurality of density values of the subject for each pixel are set. A pixel density data memory that converts the density values into bit-represented density values and stores them; a register that reads the density values of a plurality of pixels from the memory and stores them; and a register that stores the plurality of accumulated density values in a size corresponding to these density values. 1. A driving device for a light emitting element array, comprising: a density gradation circuit provided with a current conversion unit that simultaneously converts the current values into current values and outputs the current values to the light emitting elements corresponding to each pixel.