JPS63312173A - Controller for light quantity of light emitting diode array - Google Patents

Abstract

PURPOSE:To correct a light quantity with a simple and low-cost construction, by a method wherein printing information which has been changed in a multistep according to correction data from a light quantity correction data circuit is read into a driver with an enable signal divided into two or more pulses in a 1-line scanning time. CONSTITUTION:In the case of light quantity correction data for one dot is corresponding to two bits and a clock frequency is increased by four times, data for printing information is changed in pulse width according to an output value 0-3 from a light quantity correction data circuit 6A before being transferred to a shift register 1. Additionally, a latch pulse SL and an enable signal SI, which conventionally have been set to have one pulse each in a one-line scanning time, are divided into 4 pulses. The frequency of a clock pulse SC is also preset to be four times larger. In this manner, a light-emitting time of an LED element 4a can be changed in 4 steps, and the dispersion of light quantities of the respective LED elements 4a can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light amount control device for a light emitting diode array head used, for example, in an optical printer using an electrophotographic method.

[Conventional technology]

FIG. 3 is a block connection diagram showing a light amount control device for a conventional light emitting diode (hereinafter referred to as LED) array head disclosed in, for example, Japanese Unexamined Patent Publication No. 58-78476. Shift register that stores data by moving it digit by digit, 2 a latch that stores the parallel data of shift register 1 all at once, 3 a driver, 4 an LED array chip driven by this driver 3, 5 a line that takes in print data pit buffer, 6
is a light amount correction data circuit. Among these, shift register 1. Latch 21 driver 3 is one driver tC
Built into the chip.

Next, the operation will be explained. An optical printer using an electrophotographic method has one LED element 4a and one resistor 4b corresponding to one pixel dot, arranges them in a row, and controls blinking of each LED element 4a.
An electrostatic latent image is formed on a pre-charged optical semiconductor,
This is visualized through development, transferred onto recording paper, and printed.

In this optical printer, one LED element 4a is used.
Since more than 1,000 LED elements are arranged in a row, it is necessary to correct variations in the amount of light emitted from the individual LED elements 4a in order to obtain uniform print density. For this reason, the driver IC chip that drives the LED element 4a is provided with this function.

That is, the print data of each pixel dot is sent from the line pit buffer 5 to the shift register 1, and the clock S
When the transfer of 1247 minutes of print data is completed according to the input timing of c, the data in shift register 1 is stored in latch 2 at once by latch pulse SLK.

Next, based on this stored data, driver 3
Each LED element 4a of the D array chip 4 is driven. At this time, the driver 3 that drives each LED element 4a is
Since each dot is composed of four 3-state devices 3b, it is possible to select the light emission time in 16 stages based on the 4-bit light intensity correction data of the light intensity correction data circuit. Therefore, the light intensity of each LED element 4a is measured in advance, the light emission time of the LED element 4a is determined so that the light intensity is constant, and the data is input into the light intensity correction data circuit 6. Thereby, it is possible to correct the above-mentioned variations in the amount of light emitted, and it is possible to obtain good printing quality without unevenness.

[Problem that the invention seeks to solve]

Since the conventional light amount control device for the LED array head is configured as described above, it is necessary to develop a special driver IC chip that can be applied to the light amount correction data circuit 6. There were problems such as the need to change the printer interface, which inevitably increased costs.

This invention was made to solve the above-mentioned problems, and provides a light amount control device for an LED array head that can perform light amount correction with a simple and low-cost configuration while using the conventional LED array head as is. The purpose is to obtain.

[Means for solving problems]

The light amount control device for a light emitting diode playback device according to the present invention multiplies the pulse width of the print information of each pixel dot obtained from the line pit buffer in the data pulse width conversion circuit based on the correction data from the light amount correction data circuit. This converted print information is read into a driver by an enable signal that is divided into a plurality of parts within the scanning time of one line.

[For production]

The data pulse width conversion circuit in this invention converts the print information into a pulse width based on the correction data of the light amount correction data circuit before inputting the print information to the shift register,
This pulse-width-converted printing information is divided into multiple pieces within one line scanning period. According to the enable signal, each LED element of the LED array chip is driven by a driver, and the light emission time of each is individually changed. It works to correct variations in the light intensity of the elements, allowing general-purpose drivers and LED array chips to be used as is.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a shift register, 2 is a latch, 3 is a driver having a plurality of AND gates 3a that are turned on and off by an enable signal, and 4A is each AND gate 3.
An LED array chip with an LED element 4a connected to the output of a, 5 a line pit buffer containing printing information, 6A
Reference numeral 7 denotes a light amount correction data circuit that stores light amount correction data, and 7 a data pulse width conversion circuit that changes the pulse width of print information data based on the data in the line pit buffer 5 and the data in the light amount correction data circuit 6A. Note that shift register 1. Latch 2. The driver 3A is housed within one driver IC chip. In this embodiment, one driver IC chip can drive 32 dots of LED elements 4a, and one LED array chip 4A has 128 dots of LED elements 4A integrated therein.

In other words, one LED with four driver IC chips
It drives the array chip 4A.

Next, the operation will be explained. First, one line of print information input from the line pit buffer 5 via the data pulse width conversion circuit 7 is transferred to the shift register 1. When all the data of one line is transferred to this shift register 1, the data of this 1 line is stored in latch 2 at once by a latch pulse. Next, based on this stored data, the driver 3A supplies a constant current to each LED element 4a of the LED array chip 4A in accordance with an enable signal input from the outside to turn each LED element 4a on or off. do. Now, the data and latch pulse SL are obtained when each dot has 2 bits of light intensity correction data and the clock frequency is quadrupled.

Enable signal S! A timing chart of this is shown in FIG. According to this, the pulse width of the print information data changes depending on which value from O to 3 the output of the light amount correction data circuit 6A becomes. Furthermore, the latch pulse SL and enable signal 81, which conventionally had only one pulse each within one line scanning time, are divided into four pulses. Although not shown, the clock pulse Sc is also set to four times the frequency. With these, the light emission time of the LED elements 4a can be changed in four stages, and it becomes possible to correct variations in the amount of light of each LED element 4a.

In the above embodiment, each dot of light intensity correction data has 2 bits, but the number of bits may be further increased to achieve the same effect as in the above embodiment. Furthermore, in the above embodiment, the latch signal SL and the enable signal S
Although the case where both I and K have the same pulse width is shown, by changing these pulse widths, the number of correction steps can be further increased, and density unevenness can be adjusted with higher precision.

Furthermore, in the above embodiment, a unique read-only memory for storing light amount correction data was used as the light amount correction data circuit 6A, but instead of this, a random access memory is used, and density information is stored in parallel with print information. It is also possible to transfer and use it as a brightness modulation device.

〔Effect of the invention〕

As described above, according to the present invention, the pulse width of the print information of each pixel dot obtained from the line pit buffer is converted in multiple stages based on the correction data from the light amount correction data circuit in the data pulse width conversion circuit. However, this converted print information is read into the driver using an enable signal that divides it into multiple parts within one line scanning time, so before inputting the above print information to the shift register, the print density can be adjusted by the above pulse width adjustment. Therefore, even in a printer using a general-purpose driver or LED array chip, there is an effect that good printing quality without unevenness can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block connection diagram showing a light amount control device for a light emitting diode array according to an embodiment of the present invention, and FIG.
FIG. 3 is a timing chart of signals of various parts of the circuit shown in the figure, and FIG. 3 is a block connection diagram showing a conventional light amount control device for a light emitting diode array. 1 is a shift register, 2 is a latch, 3A is a driver,
4A is an LED array chip, 6A is a light amount correction data circuit, and 7 is a data pulse width conversion circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant Mitsubishi Electric Co., Ltd. Agent Patent attorney 1) Hiroshi Sawa (2 others) Figure 1 Figure 2 (Sl)

Claims (1)

[Claims] After storing the printing information of each pixel dot from the line pit buffer in the shift register one line at a time, this is stored all at once in the latch, and based on this stored data, the driver drives each light emitting diode in the light emitting diode array. , in a light intensity control device for a light emitting diode array that corrects variations in the light intensity of each light emitting diode using a light intensity correction data circuit, the pulse width of the print information from the line pit buffer is multi-staged based on the correction data of the light intensity correction data circuit. A data pulse width conversion circuit is provided, and the print information whose pulse width has been converted by the data pulse width conversion circuit is read into the driver by an enable signal that is divided into a plurality of parts within the scanning time of one line. A light amount control device for a light emitting diode array, characterized in that: