JPH05177872A - Gradation control method in dot image output device - Google Patents

Abstract

PURPOSE:To obtain a gradation control method ensuring a high-accuracy, fine luminance gradation without complicating a circuit construction while compensating a luminance variation in chip characteristics esp. in a line dot printer, such as an LED printer. CONSTITUTION:A pixel as a component of a dot image is divided into P unit elements in a sub-scanning direction. While a drive current is appropriately selectively supplied to the divided unit elements for substantially insreasing or decreasing the unit elements, the level or supply time of the drive current to be supplied is controlled stepwise. In this manner, a gradation control for pixels is accomplished. In this case, it is preferable for the accomplishment of a smooth gradation control that the control is conducted stepwise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer such as an LED printer which forms a matrix dot image corresponding to image information and a display such as a CRT display which forms a matrix bitmap and other images. The present invention relates to a gradation control method in an output device.

[0002]

2. Description of the Related Art Conventionally, recording is performed on a photosensitive drum or the like that relatively moves in the sub-scanning direction while controlling the lighting of LED arrays arranged in one line in the main scanning direction at the same time for one line or in block units based on video data. LED printers and other dot printers that form a matrix of pixel patterns on a material are known.

Among the printers of this type, the latter time-division driving method, that is, the LED array for one scanning line is divided into a plurality of blocks (m) by n bits, and the divided block units (usually chip units) The configuration of the LED drive circuit in the time-division drive system in which the LED elements are sequentially controlled to be turned on by means of FIG.
In the array, m LED chips 1a ... Incorporating n-bit LED elements are arranged in a row to form an array.

Reference numeral 10 denotes a source driver, which has a shift register 11 and a latch circuit 1 each having a memory capacity corresponding to the number n of LED elements in each block as shown in FIG.
2 and a constant current driver 13, n LEDs
The n-bit serial data controlled in the element chip unit is input to the shift register 11 and read in synchronization with CLK, the data is latched in parallel by the latch signal in the latch circuit 12, and then latched by the constant current driver 13. The lighting of the LED element corresponding to the data is controlled. Reference numeral 14 is a common driver, which is the LED chip 1a.
The connection with ... is switched to the starting, next, and next-to-one chips,
By sequentially controlling the lighting of the corresponding chip by the source driver 10, time-division lighting control is enabled.

In such an LED printer, a method of controlling the gradation of each pixel is proposed in Japanese Patent Laid-Open No. 59-127468. To explain such a configuration based on FIG. 6,
In the conventional device, one LED element 100 is connected to the circuit power source through one current limiting resistor 101 and one switching element 102. However, in this conventional technique, the current limiting resistor 101 and the switching element 102 are used. A plurality (n) of constant current elements 103A and 103B are provided and connected in parallel, and pixel data for controlling lighting of the LED element 100 is supplied to the constant current elements 103A and 10B.
3B corresponding to n-bit multi-valued data, and using each bit of the multi-valued data, the constant current element 1
03A and 103B are configured to be appropriately drive-controlled. Reference numeral 104 is a switch element on the common driver side.

[0006]

In such a prior art, 2 ⁿ luminance gradation control is possible by driving and controlling one pixel (LED element) by a plurality of constant current elements. In order to realize a tonal brightness gradation, eight constant current elements are required and the circuit configuration becomes complicated.
In order to solve such a defect, the constant current circuit is configured by one constant current element, and the binary data is added to the pixel data as in the conventional case without using the n-bit multi-valued data as described above. While using, the pulse width modulation of the binarized data is performed according to the degree of pixel gradation, and the driving time of the LED element is controlled according to the pulse width to perform the brightness gradation control. ..

However, even with such a technique, it is not only difficult to realize a fine luminance gradation of 256 gradations only by controlling the driving time of the pixel (LED element), and especially in the LED chips 1a. Due to the influence of the chip characteristics, variations in luminance occur among the chips, so it is practically almost impossible to perform the tone control of 256 tones while compensating for these variations.

In view of the above-mentioned drawbacks of the prior art, the present invention, particularly in a linear dot printer such as an LED printer, accurately compensates for variations in chip characteristic brightness without complicating the circuit configuration. It is also an object of the present invention to provide a gradation control method capable of performing a fine luminance gradation.

[0009]

According to the present invention, one pixel forming a dot image is divided into P unit elements in the sub-scanning direction, and a drive current is appropriately and selectively supplied to the divided unit elements. The gradation control of the pixel is achieved by stepwise controlling the supply current level or supply time of the pixel while substantially increasing or decreasing the unit element. In this case, the control is preferably stepwise control in order to smoothly achieve gradation control.

[0010]

According to such a technical means, for example, one pixel is divided into four unit elements, and a drive current is appropriately and selectively supplied to the unit elements to substantially increase or decrease the unit element while supplying the unit element. As a result, 256 gradations of (2 ⁴ : unit element) * (2 ⁴ : driving current) are achieved by controlling the driving current to be controlled in four steps. That is, as shown in FIG. 1A, each unit element 5A ...
By increasing or decreasing the number of pixels, the size of the pixel dot can be apparently controlled in gradation while the position is shifted, and as shown in FIG. 1B, the drive current supplied to each unit element 5A ... Is controlled in four steps. As a result, the size of the unit element 5A ... Can be controlled, and 256 gradations can be smoothly achieved by the combination of both.

In the present invention, although the stepwise control of 2 ⁸ is carried out, the number of constant current element means necessary for controlling the drive current is not four but four, which simplifies the circuit structure. .. Further, according to the present invention, the driving current is not controlled in steps of 256 gradations but is controlled in four steps of, for example, 25%. Therefore, the brightness variation of the LED elements in each chip is 5
Even if it is about%, stepwise control is possible while substantially compensating for the error. Of course, in this case, it is possible to control the gradation by taking the above error into consideration. In addition, the present invention, in particular, in order to compensate for the variations between the chips, the LE of the time-division drive system is used.
By controlling the drive time on the common driver side in the D printer and controlling the drive current of each unit element 5A ...
It is possible to perform gradation control while compensating for variations between chips.

In this case, since the signal applied to the common driver side has a time width (pulse width) n times that of the signal applied to each LED element, the pulse width modulation does not speed up the clock. Fine and accurate pulse width modulation is easy, and high-quality pixel dots can be formed.

As a technique similar to the present invention, one pixel forming a dot image has P unit elements 5A ...
An image output method in which a pixel pattern is output in units of n bits in which one scanning line or one scanning line is divided into m while repeatedly applying the same drive current to each of the divided unit elements 5A ... 266
No. 26 and Japanese Patent Application Laid-Open No. 60-134660, all of them are intended for pixel division for the purpose of improving the quality, and the unit elements 5A ... There is no idea of controlling the drive current of 5A.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below as an example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Not too much. Figure 2
4 is a configuration diagram of a main part of an LED drive circuit according to an embodiment of the present invention, and an internal configuration diagram of a source driver shown in FIG. 4, showing only a drive power source portion for driving each LED element for simplifying the description. ..

Decoder 3 decodes 4-bit unit density gradation multi-valued data corresponding to the number of constant current elements to generate four kinds of binary serial data corresponding to each constant current source element. Reference numeral 10 denotes a source driver, which includes four shift registers 11A for serially fetching the serial data at the same timing in synchronization with the clock, and four latch circuits 12A for latching the n-bit serial data in parallel each time the serial data is fetched. , A 4 × n constant current element 13 driven and controlled by a latch signal from the latch circuit 12A.
It is composed of An ...

The constant current elements 13An ...
The first constant current element 13A1 has an output of 1 mA, the second constant current element 13A2 has an output of 2 mA, and the third constant current element 13A3 has an output of 4 mA. The output of the fourth constant current element 13A is 8 mA.
, And the outputs of the four constant current elements can be selectively driven and controlled by the four latch circuits 12A.

To briefly explain the operation of the driving circuit, first, the first LED chip 1a is based on the clock.
While converting the density gradation data corresponding to the unit pixel 5A group for driving ... into four binarized data serially by the decoder 3, the data is serially transferred to the corresponding shift register 11A at the same timing. After the data is stored in a complicated manner, the data is latched in parallel by the respective latch circuits 12A ... In response to a latch signal from a control circuit (not shown), and the corresponding constant current elements are driven based on the latch data. .. As a result, the four constant current elements are drive-controlled by the data D1, D2, D3, and D4 corresponding to the respective LED elements, which are input to the four shift registers 11A ... And the total amount of the current becomes the LED drive current. Therefore, the LED drive current is the constant current element 13An.
By appropriately selecting ..., gradation control in 16 steps from 0 to 15 mA in units of 1 mA becomes possible.

After the data is transferred to the latch circuits 12A ... To the shift registers 11A ... The binarized data for driving the next LED chips 1A ... Is serially sent to each shift register 11A. After the data is stored, the data is latched by the respective latch circuits 12A ... Side based on the latch signal after the data is stored, and the chip selection signal is transmitted from the control circuit to the common driver 14 to connect the source driver 10 to the next position. The LED chip 1B is switched to the LED chip 1B, the next LED chip 1B is driven and controlled in the same manner as described above, and the same operation is continuously performed m times. To do. The chip selection signal is transmitted to the switch element 104 in the common driver 14 in the pulse width modulation circuit 5, and the data pulse width modulated according to the luminance characteristics of each chip.

The LED chips 1a ... 1A are then processed in the same manner.
By performing the drive control of 1N m times (N × m times) × 4 times, the pixel data of one scanning line as the unit element 5A group divided into four as shown in FIG. 1 is developed. At this time, the density gradation data for driving the first unit element 5A group and the density gradation data for driving the second unit element 5B group are naturally different, and even the so-called black data is as described above. Selectively select each unit element 5A ...
Are driven / non-driven to substantially increase / decrease the driving unit elements 5A.

In the above embodiment, one source driver 10 is used.
Four shift registers 11A ... And a latch circuit 12
.. and 4n constant current elements 13An are built in to form a new driver, but one shift register 11 and a latch circuit 12, as shown in FIG. In addition, the existing source driver 10 (FIG. 5) that has n constant current elements 13n corresponding to the number of LED elements
It is possible to construct an apparatus capable of achieving the operation of the present invention by using a plurality of the above (see). That is, the first source driver 10A
The output of the constant current element built in is 1 mA, and the output of the constant current element built in the second source driver 10B is 2 m.
A, the output of the constant current element built in the third source driver 10C is set to 4 mA.
If the outputs of the LED devices 0A ... Are connected in parallel and one LED is driven by the selected one or more source drivers A ... .

[0021]

As described above, according to the present invention, particularly the LED
In a line dot printer such as a printer,
It is possible to perform accurate and precise luminance gradation while compensating for variations in luminance of chip characteristics without complicating the circuit configuration. And so on.

[Brief description of drawings]

FIGS. 1A and 1B show gradation-controlled pixel data formed by the present invention.

FIG. 2 is a block diagram showing an internal configuration of a source driver of the LED drive circuit according to the embodiment of the present invention.

FIG. 3 is a block diagram of a main part of an LED drive circuit according to an embodiment of the present invention.

FIG. 4 shows a block diagram of an LED drive circuit in the prior art.

5 is an internal configuration diagram of the source driver of FIG.

FIG. 6 is a circuit diagram of a main part of an LED driving circuit in the related art in which gradation control is performed.

[Explanation of symbols]

 1a LED element chip 100 LED element 5 Pulse width modulation circuit 11A Shift register 12A Latch circuit 5A-5B Unit element

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 25, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Figure 3]

[Figure 6]

[Fig. 2]

[Figure 4]

[Figure 5]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B41J 2/52 H04N 1/40 B 9068-5C

Claims (2)

[Claims] 1. A pixel forming a dot image is divided into a plurality of unit elements in the sub-scanning direction, and a drive current is appropriately and selectively supplied to the divided unit elements to substantially increase or decrease the unit element. A gradation control method in a dot image output device, characterized in that the drive current level or current supply time to be supplied is controlled stepwise 2. The LED array for one scanning line is divided into one or a plurality of chip units, and the L is divided into chip units according to a chip selection signal supplied to a common driver.
The dot image output apparatus according to claim 1, wherein the ED element is driven in a time-division manner, wherein the gradation control is performed while the brightness is corrected by the selection signal whose pulse width is modulated corresponding to the variation in the corresponding chip brightness. Characteristic gradation control method