JP2919085B2 - Light intensity correction method for luminous body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-division driving light amount correcting method for a light-emitting element, and more particularly to a method in which a large number of light-emitting elements arranged in a line like an LED head array are divided into blocks. The present invention relates to a light amount correction method for a light emitter that performs light amount correction in units.

[0002]

2. Description of the Related Art Heretofore, printers using an exposure system for writing a latent image while controlling the lighting of an LED head having a large number of LED elements arranged in a row along the main scanning direction in accordance with image information have been known. Various types of image forming apparatuses are known. This type of LED head includes a one-line type head that simultaneously controls lighting of an LED element group for one scanning line according to image information, and an LED element for the one scanning line. There is a time division type LED head in which a group is divided into a plurality of blocks (m) by n bits and the LEDs are sequentially controlled to be turned on in units of the divided blocks. miniaturized further has been adopted a number one when division of the latter in order to achieve stabilization of the light quantity.

Such a time-division type LED head is generally formed into an LED chip for each of the blocks, and each of the chips is based on a shift register for inputting n-bit data serially, a latch circuit, and parallel data from the shift register. The LED chip is configured by connecting a driving IC incorporating a driving driver for controlling the light emitting elements in the chip. It has variations in luminance (light output) characteristics. Therefore, in order to obtain a stable light output between chips, various methods have been proposed for correcting the energization time or the drive voltage (current) for each chip in accordance with the luminance characteristics. (Actual fairness 1-2180
5, JP-A-1-297271, JP-A-59-13227
6 others)

[0004]

However, all of the above-mentioned prior arts are correction means taking into account the luminance characteristics of only the LED chip, and are not light amount correction means for the LED head as a whole incorporating the driving IC. That is, the LED
The chip is connected to a drive driver for controlling the driving of each light emitting element, a common driver for setting the current supply time while sequentially switching the LED chips, and the like.
Since the rise or fall characteristics of these drivers are different for each chip, and the characteristics of the drivers fluctuate due to deterioration over time, the actual light emission time of each chip is Due to variations in characteristics, the correction considering the luminance characteristics of only the LED chip makes it difficult not only to accurately correct the light amount of the entire head, but also, in particular, the falling characteristic of the driver. Is reduced, for example, an overlap may occur between the power supply end time of the current chip and the power supply start time of the next chip, and the image may be disturbed.

In order to solve such a drawback, in the prior art, the overlap is considered in advance and the power supply time of the chip is shortened accordingly. it was addressed in that a lot of that amount driving current in order to obtain a light output, as the downsizing of recent years the LED head as the, or to increase the density of the dot density of the chip As the number of time divisions is increased, the increase in the drive current is limited, and a predetermined optical output may not be obtained.

According to the present invention, it is possible to accurately obtain a uniform light output in the column direction by taking into account the variation in characteristics or deterioration over time of not only the LED chip but also a driving driver and a common driver connected to the chip. It is an object of the present invention to provide a method for correcting a light amount of an LED array or other light emitter.

Another object of the present invention is to allow the width of the energizing pulse for each chip to be as large as possible without substantially causing the above-mentioned drawbacks caused by the overlap, thereby preventing the drive current from being unnecessarily increased. Another object of the present invention is to provide a light-emitting element light amount correction method which can easily increase the number of chip time divisions and can thereby achieve a reduction in head size and a high dot density.

[0008]

SUMMARY OF THE INVENTION The present invention provides a linear arrangement
A large number of light emitting elements are divided into m units in blocks, and
Drive the light emitting element while sequentially switching the
In the method for correcting the light amount of a light emitter for controlling, the light emitting element
Preparing the light emission characteristic data of the child in advance and adjusting the voltage applying means
To set the light emitting element drive current.
Current correction means and a voltage corresponding to the light emitting element drive current
Is output when the voltage is equal to or higher than a predetermined voltage of the voltage applying means.
At the time of overlap due to the overlap detection pulse
Measuring means for measuring the interval (Pb), which is set in advance
To the block switching signal generated sequentially by the pulse width
Time-division driving while sequentially switching each block based on
The overlap between adjacent blocks.
When the block time is switched by the measuring means (Pb)
Measured on the basis of the variation time of the resulting drive current to the onset
From the main scanning time of the optical element, the m of the light emitting element divided into m
Calculate the effective light emission pulse width (Po) of the lock
Between the effective emission pulse width and the overlap time.
The difference (Po-Pb) is taken, and the difference (Po-Pb) is
The adjustment setting value of the voltage adding means is obtained from the optical characteristic data.
Te, JP that corrects the drive current of the light emitting element blocks
Sign.

[0009] In this case, the correction without be completed in only one detection scan, the second feeds back the hear dynamic current before obtained by the one detection scan, a third detection scanning and confirm its By doing so, more accurate light quantity correction becomes possible.

Incidentally, the measurement of the overlap time is generally performed based on the fluctuation time of the drive current generated at the time of the block switching. However, when such a measuring means is employed, each chip is normally operated. It is premised that no abnormal current such as driving and simultaneous lighting of a plurality of chips is generated. Therefore, in such a case, it is necessary to measure the overlap time after detecting that the drive current of each corresponding block is within a predetermined reference level. This is specified by the second aspect of the present invention.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just.

FIG. 1 shows a control circuit for an LED array according to an embodiment of the present invention.
Is LE through the overlap detection circuit 3 which is also used for abnormality detection.
An LED anode source power supply that supplies an output voltage to the D head 5, and is configured to be capable of emergency shutdown based on an abnormality detection signal from the overlap detection circuit 3.

The LED head 5 has, for example, 128 LEs.
An LED array 5e in which 20 LED chips 5eA... Incorporating D elements 5e1A... Are arranged in a line, and a source shift register 5a having a memory capacity corresponding to the number of LED elements for each of the chips 5eA. , Latch circuit 5
b, the number of source drivers 5c and the number of constant current circuits 5d corresponding to the number of LED elements (128) are respectively provided.

Reference numeral 6 denotes a switching control circuit, which controls each LED chip 5e.
A. 20 common drivers 6b connected to the cathode side of A. and corresponding LEDs via the common drivers 6b
It comprises a block shift register 6a for selectively switching the connection with the chips 5eA... Sequentially.

FIG. 2 is a diagram showing the internal configuration of the overlap detecting circuit 3. The detecting resistor 31 converts the driving current to the LED array 5e into a voltage, and the input / output terminals 2a of the detecting resistor 31 are connected.
A differential amplifier 32 that amplifies the detection voltage Vc of 1 / 2a2,
A reference voltage circuit 33 for generating a reference voltage Vs corresponding to a reference current Cs or a chip reference average current Cx for each of the chips 5eA..., A comparator 34 for comparing the two voltages,
An AND gate 35 for ANDing a comparison output from the comparator 34 with a detection pulse signal for overlap described later, and a detection voltage Vc corresponding to the chip drive current as shown in FIG.
Is higher than the reference voltage Vs, a comparator 34 outputs a comparison output to an AND gate 35. The comparison output and an overlapped detection pulse signal are ANDed to obtain the AND gate 3.
Overlap time control unit of the drive current between the respective chips 5EA ... adjacent on the basis of the detection output PD to 5 is the output
It is measured on one side.

On the other hand, while the control unit 1 is outputting an abnormality detection pulse, the reference voltage circuit 33 is connected to the chip / chip to make the detection circuit 3 function as an abnormality detection circuit.
A reference voltage corresponding to the withstand current strength of the driver is generated,
The voltage corresponding to the driving current of each corresponding chip 5eA is compared with the reference voltage by the comparator 34 , and when the detected voltage becomes equal to or higher than the reference voltage, the comparator 34 outputs a comparison output.
The output is output to an AND gate 35 , the comparison output and the abnormality detection pulse are ANDed, and the LED anode source power supply 2 is urgently shut down based on an error detection signal output from the AND gate 35 . . 7 is a current correction means.
The A / A converter serves as a reference power supply for operating the constant current circuit 5d, and a desired constant current can be set by changing the reference voltage from the control unit 1 side.

Next, the control operation of this embodiment will be described focusing on the light amount correction means. A) Pre-setup step First, each chip 5eA arranged in the LED array 5e
The light emission characteristics of each of the measured values are actually measured in terms of current value (C), the measured data is multiplied by a reference pulse (P) to calculate a reference pulse width current product (CP), and the current product is stored as an initial value. deep.

B) Actual Machine Setup Step Next, after dividing the main scanning time T by the number of chips m to calculate an effective light emission (maximum) pulse width (Po: T / m), the initial value is calculated using the pulse width Po. By dividing CP (CP / Po), a reference current (Cs: CP / P) for each chip 5eA.
o) and the average value of all the reference currents (Cx: ΣCs / m) is calculated.

C) Actual Machine Correction Step First, the first scan line (detection scan line) is time-division driven based on the block switching signal based on the predetermined pulse width Po, and the reference current is supplied to each chip 5eA. Cs or uniformly output the reference average current Cx to control the energization, grasp the overlap state, and detect a detection output PD corresponding to the overlap state.
Get. During the detection scanning, it is preferable to input detection data 1c for each chip 5eA... All LED elements to emit light to the source shift register 5a in order to improve accuracy, not actual image data.

More specifically, after the output enable 1a is output from the control unit 1, the detection data 1c is serially input to the source shift register 5a based on the source shift clock 1d, and n bits of the detected data are input. After the data 1c is stored in the register 5a, the block switching signal 1e is output to the block shift register 6a and the latch signal 1b is output to the latch circuit 5b at the same time. The current of the circuit 5d is set to the reference average current Cx, and the corresponding chip 5eA by the n-bit data latched by the latch circuit 5b. All the LED elements generate the next block switching signal 1e based on the reference average current Cx. It is energized (emitted) for a time (pulse width Po) until output.

On the other hand, an abnormality detection pulse 1h is output from the control unit 1 within the energization pulse time, and the reference voltage of the reference voltage circuit 33 is switched to a reference voltage corresponding to the withstand current strength. .. Are detected by the overlap detection circuit 3, and when no error detection signal is output from the detection circuit 3, an overlap detection pulse 1i is output. Note that the overlap detection pulse 1i rises before the next switching signal is output, and the time width of the overlap detection pulse 1i is set to O while the actual overlap occurs.
The pulse time width is set so as to be N.

Next, when the overlap detection pulse 1i is output, the reference voltage of the reference voltage circuit 33 is switched to the reference voltage Vs corresponding to the chip reference average current Cx. Perform overlap detection operation. The abnormal detection pulse 1h and the overlap detection pulse 1i are alternately output, and the abnormality detection operation and the overlap operation are performed for each chip 5eA... Based on the block switching signal, and the adjacent chips 5eA.
The measurement of the overlap time Pb for each interval is performed until one scan line is completed.

After the end of the one scanning line, the overlap detection time Pb is subtracted from the effective light emission pulse width Po, and the primary detection pulse width (PW ': Po- Pb ) and the initial value CP are calculated using the primary detection pulse width PW'. The control unit 1 calculates the primary detection reference current (CW ′: CP / PW) thus divided.
Then, the detection operation is performed again based on the calculated primary detection pulse width PW ′ and primary detection reference current CW ′ to obtain a secondary detection pulse width PW and a secondary detection reference current CW.

Thereafter, in order to further improve the accuracy, a tertiary and quaternary detecting operation or a confirming operation are performed as necessary. Then, the chip switching is performed based on the block switching signal generated by the detecting pulse width PW and the reference current PW. By performing actual time-division driving of the array 5e, accurate light amount correction can be performed. It is also possible to add a one-step pulse of a minute clock to the detection pulse width PW so that the drive current slightly overlaps so as not to substantially affect an image. Can be reduced.

[0025]

As described above, according to the present invention, not only the LED chip but also a driver and a common driver connected to the chip for correcting the amount of light of a light-emitting body such as an LED head employing a time-division driving method. It is possible to accurately obtain a uniform light output in the column direction by taking into account variations in the characteristics of the driver or deterioration over time. Further, according to the present invention, it is possible to take as much as possible the energizing pulse width of each chip without substantially causing image distortion or the like due to overlap,
This makes it possible to easily increase the number of chip time divisions without unnecessarily increasing the drive current, thereby achieving a smaller head and a higher dot density.

[Brief description of the drawings]

FIG. 1 is a control circuit of an LED array according to an embodiment of the present invention.

FIG. 2 is an internal configuration diagram of an overlap circuit.

FIG. 3 is a time chart showing the control operation of FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Control part 2 Source power supply 3 Overlap circuit 5 LED head 6 Switching control circuit

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/44 B41J 2/45 B41J 2/455

Claims (2)

(57) [Claims] 1. A large number of light emitting elements arranged in a line are
Lock unitmDivide and cut the block in time division
Light amount of the luminous body for controlling the driving of the luminous element while changing
In the correction method,Prepare light emission characteristic data of the light emitting element in advance, The driving current of the light emitting element is adjusted by adjusting the voltage applying means.
Current correction means capable of adjusting and setting The voltage corresponding to the light emitting element driving current is equal to the voltage applied.
Output when the voltage is higher than the predetermined voltage of the
The overlap time (Pb) is measured by the detection pulse
Measurement means  With a preset pulse widthSequentiallyGenerated bro
Do not sequentially switch each of the blocks based on the block switching signal.
While performing time division driving,
The overlap time (Pb) is measured by the measuring means.
Based on the drive current fluctuation time that occurs during lock switching
Measure, The light emitting element divided into m from the main scanning time of the light emitting element
When calculating the effective light emission pulse width (Po) of the child block,
In both cases, the effective emission pulse width and the overlap time
And the difference (Po-Pb) from the difference (Po-Pb)
From the light emission characteristic data, the adjustment set value of the voltage applying means
Get,  The light emitting element blockDriveThe feature is that the dynamic current is corrected.
Light amount correction method of the illuminant to be performed. 2. The light amount correction method according to claim 1, wherein the measurement of the overlap time is performed based on a fluctuation time of a drive current generated at the time of the block switching. A light amount correction method which is performed after detecting that a current is within a predetermined reference level.