JPH09311664A - Light emitting element controller using pnpn thyristor structure, controlling method therefor, and storage medium thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To approximately correct the luminance deviation between a plurality of light emitting elements so as to dispense with previous characteristic measurement. SOLUTION: For controlling the light quantity of a light emitting element array using a PNPN thyristor structure, the cathode resistance of a light emitting element is measured during light emission of a light emitting element Sr1, and the cathode resistance measurement result is fed back to a light emission control signal, so that a luminance deviation between respective light emitting elements is corrected approximatively. For example, a voltage V and a current I of the light emitting element are detected, and the voltage V and the current I are passed through a logarithmic conversion unit U3, a differential arithmetic unit U4, and an inverse logarithmic conversion unit U5, and as a result, a cathode resistance R(=V/I) of the light emitting element is obtained. The resistance R is inputted into one side of the comparison unit U6, while to the other terminal, a value C obtained by integrating an inverted pulse of the image data is inputted. When the resistance R corresponds to the value C, an output D of the unit U6 is reversed so as to turn off the light emitting element via an OR gate G1. Therefore, a lighting time is shortened as the resistance R lowered further (that is, as the light emitting luminance is larger).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element control device using a PNPN thyristor structure, a control method therefor, and a storage medium, and a product using the light emitting element, for example, a light emitting element arranged linearly, It is suitable for an electrophotographic image forming apparatus (for example, an LED copying machine or an LED printer) used as an exposure apparatus.

[0002]

2. Description of the Related Art A light emitting device used in an electrophotographic exposure apparatus is, for example, an LED array. Each LED
Each (light emitting diode) has a variation in light emission brightness. In order to correct this variation, conventionally, after measuring the light emission characteristics of each LED in advance, the measurement result is stored in a memory and exposure is performed. At that time, the stored information is read from the memory and the light emission of the LED array is corrected and controlled.

[0003]

However, in the above-mentioned conventional example, since the light emission characteristic of the LED is measured and stored in the memory or the like in advance, the work of performing the measurement and the storage means such as the memory are required. Become.

The present invention has been made in view of the above points, and an object thereof is to approximately correct the luminance variation of each light emitting element in the control of a plurality of light emitting elements without using a storage means. To be able to do it.

Further, a further object of the present invention is to enable the above-mentioned correction control in real time at the same time as the start of lighting, thereby eliminating the need for a measuring operation for measuring and storing each brightness in advance, thereby improving the efficiency of product production. Is to improve.

[0006]

In order to achieve the above object, the present invention utilizes the fact that in a light emitting device array using a PNPN thyristor structure, there is a correlation between the emission brightness and the cathode resistance of the light emitting device, and During the light emission of the element, the cathode resistance of the light emitting element is measured, and the cathode resistance measurement result is fed back to the light emission control signal to control the light emission.

According to the present invention, with the above structure, the variation in brightness of each light emitting element can be approximately corrected, and this correction control can be performed in real time at the same time as the start of lighting.

More specifically, the present invention relates to a control device for a light emitting element using a PNPN thyristor structure, which is a PNP.
A light emitting element using an N thyristor structure, and a signal generating means for outputting a light emission control signal for controlling light emission of the light emitting element,
Measuring means for measuring the cathode resistance of the light emitting element, and measuring the cathode resistance by the measuring means while the light emitting element is emitting light, and feeding back the measurement result to the light emission control signal to cause the light emitting element to emit light. And control means for controlling.

As a preferred form of the present invention, the measuring means includes a voltage detecting means for detecting a cathode voltage of the light emitting element, a current detecting means for detecting a cathode current of the light emitting element, and the voltage detecting means. Logarithmic conversion means for respectively logarithmically converting the output of the means and the output of the current detection means,
The logarithmic conversion means has a difference calculation means for calculating a difference between the outputs and an inverse logarithmic conversion means for performing an inverse logarithmic conversion on the output of the difference calculation means, and the output of the antilogarithmic conversion means corresponds to the measurement result. It can be characterized by: As another form thereof, the measuring means includes a voltage detecting means for detecting a cathode voltage of the light emitting element, a current detecting means for detecting a cathode current of the light emitting element, an output of the voltage detecting means and the current. It is also possible to have a calculating means for calculating the cathode resistance value of the light emitting element from the output of the detecting means.

In a preferred mode of the present invention, the control means includes an integration means for integrating the light emission control signal,
It may be characterized by further comprising: comparing means for comparing the measurement output of the measuring means with the output of the integrating means; and logic means for suppressing the light emission control signal according to the comparison result of the comparing means.

In a preferred embodiment of the present invention, the light emission control signal is an image signal. Further, the light emitting element can be a light emitting element array that constitutes an exposure device of an electrophotographic printer. Further, the light emitting element may be a light emitting element array which constitutes a print exposure apparatus of an electronic device having a built-in electrophotographic printing mechanism. The electronic device incorporating the electrophotographic printing mechanism may be, for example, a facsimile machine.
Further, the light emitting element may be a light emitting element that constitutes a display device.

According to the method of the present invention, in the method of controlling a light emitting device using a PNPN thyristor structure, the fact that there is a correlation between the cathode resistance of the light emitting thyristor and the light emission brightness is utilized, and the light emitting device is emitting light during the light emission. The cathode resistance is measured and the measurement result of the cathode resistance is fed back to the light emission control signal of the light emitting element to approximately correct the luminance variation of each light emitting element. Then, during the light emission of the light emitting element, a measurement step of measuring the cathode resistance of the light emitting element, and a control step of returning the measurement result of the measurement step to the light emission control signal to control the light emission of the light emitting element. And can have.

In a preferred mode of the method of the present invention, the measuring step includes a voltage detecting step of detecting a cathode voltage of the light emitting element, and a current detecting step of detecting a cathode current of the light emitting element, A logarithmic conversion step for logarithmically converting the detection result in the voltage detection step, a difference calculation step for calculating a difference between the logarithmic conversion results in the logarithmic conversion step, and an inverse logarithmic conversion for the calculation result in the difference calculation step. And an inverse logarithmic transformation step. The measuring step includes a voltage detecting step of detecting a cathode voltage of the light emitting element, a current detecting step of detecting a cathode current of the light emitting element, a detection result of the voltage detecting step and a detection of the current detecting step. And a calculation step for calculating the cathode resistance value of the light emitting element from the result.

Further, in the method of the present invention, the control step includes an integration step of integrating the light emission control signal, a comparison step of comparing the measurement result of the measurement step with an integration result of the integration, and the comparison. A lighting control step of suppressing the light emission control signal according to the comparison result of the step can be included.

A storage medium storing the processing procedure of each step of the method of the present invention is included in the present invention.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a circuit configuration of a light emitting element array using the PNPN thyristor structure used in the embodiment of the present invention. The light emitting elements of this light emitting element array are Self-scanning Light Emitting Devices (S:
It is called as LED).

This SLED is disclosed in the literature: JP-A-1-238.
No. 962, No. 2-208067, No. 2-212170, No. 3-20457, No. 3-1994968, No. 4-587.
No. 2, JP-A-4-23367, JP-A-4-2.
96579, JP-A-5-84797, Japan Hardcopy '91 (A-17) "Light Emitting Element Array for Optical Printer Integrated with Driving Circuit", and Proceedings of IEICE Spring Conference ('90. 3.5) "PNPN
Self-scanning light emitting device (SLE) using thyristor structure
D) ”etc.

The structure of this SLED will be described with reference to FIG. As shown in FIG. 1, each of the light emitting thyristors T (1) to T (5) has a PNPN4 layer structure, has two emitter layers on both sides and two base layers in the middle, and the substrate (P type) serves as the anode 1. The cathode electrode 2 is attached to the uppermost layer (N type) which is the emitter layer, and the gate electrode 3 is attached to the P type intermediate layer which is the base layer.

It is known that an S-shaped negative resistance characteristic is formed between the anode and the cathode of the thyristor, and the turn-off voltage V _c-on of the cathode depends _on the gate voltage VG. That is,

[0021]

## EQU1 ## V _c-on = V _G -V _dif (V _dif : diffusion potential) (1) To turn off the thyristor, the cathode voltage can be raised to zero volts. The gate terminal in the ON state is pulled up to the anode potential (zero volt).

T (1) of a light emitting thyristor which is an SLED
Gate terminals 3 from T to T (5) are sequentially connected via a diode D, and a power supply VGA is connected through a load resistance PL.
Connected to.

FIG. 2 shows the pulses applied to the SLED of FIG. Transfer clocks Φ1 and Φ2 are applied to the cathode 2 for the transfer operation. The transfer clock Φ1 is applied to the thyristors of T (1), T (3) and T (5), and the transfer clock Φ2 is applied to the thyristors of T (2) and T (4). . At the start of transfer, a start pulse ΦS is applied to the gate 3.

Now, assuming that the thyristor of T (3) is in the ON state by the low level voltage of the Φ1 clock, the gate potential (zero volt) in the ON state affects the thyristor T (4) on the right side through the diode D. give. Since only the element on the right side is selectively turned off by the low-level voltage of the next Φ2 clock, light emission can be transferred rightward.

FIG. 3 shows the light emitting thyristors Sr1 to Sr5 and the shift thyristor (transfer thyristor) for driving the light emitting thyristors on the same wafer by utilizing the above-described shift register function and light emitting function of the light emitting thyristors. )
The equivalent circuit of SLED for electrophotographic printers which combined Sr1'-Sr5 'is shown. The pulse ΦS shown in FIG.
By applying the pulse ΦD to each signal line according to Φ1, Φ2 and the image data, only the light emitting thyristor corresponding to the image data can be turned on.

The amount of light emitted from the light emitting thyristor can be controlled by controlling the cathode current or controlling the light emitting time. Usually, since the light emitting thyristors have different light emitting efficiencies, when used in an electrophotographic printer or the like, it is necessary to make a correction to make the light amounts of the respective light emitting thyristors uniform.

In the present invention, the correlation for the cathode resistance of the light-emitting thyristor and the light-emission brightness is utilized to make an approximate correction for the light amount. It is already known that the cathode resistance and the brightness have a gentle inverse proportional relationship.

FIG. 4 shows the configuration of a light emission control circuit according to an embodiment of the present invention. ΦD of image data pulse is OR gate G
1 is applied to one terminal of the PNP transistor T
r1 is turned on, and the light emitting thyristor Sr1 is turned on.
The voltage and current of the light emitting thyristor Sr1 are detected by the voltage detection unit U1 and the current detection unit U2, and the respective detection values V and I are converted into LogV and LogI values through the respective logarithmic (Log) conversion units U3. To be done.

These LogV and LogI are further calculated to Log (V / I) in the difference calculation unit U4, and then V / V is calculated by the inverse logarithm (Log-1) conversion unit U5.
I, that is, the resistance value R is converted. The resistance value R corresponds to the measured value of the cathode resistance of the light emitting thyristor Sr1.

The value of R is input to the minus side of the comparison unit U6. On the other hand, the image data pulse ΦD is also input to the integration unit U7 through the pair of inversion gates G2. Therefore, the output of the integration unit U7 increases with time at the same time when the light emitting thyristor Sr1 is turned on. The output of the integrating unit U7 is input to the plus side of the comparing unit U6, and when the input value exceeds the value of R, the output of the comparing unit U6 is inverted. This comparison unit U
The output of 6 is input to the other terminal of the OR gate G1, and when the output is inverted, it operates to turn off the light emitting thyristor Sr1.

FIG. 5 shows the image data pulse ΦD and the above-mentioned OR.
Waveform of the output point A of the gate G1, the above comparison unit U6
Waveforms of a negative input point B, a positive input point C, and an output point D are shown respectively.

With the configuration described above, the light emitting thyristor having a smaller resistance value, that is, the light emitting thyristor having a higher light emission luminance, has a shorter lighting time, and the light quantity of the light emitting thyristor can be approximately uniformly corrected. Further, in the SLED, since the light emitting thyristors are continuously connected, the circuit of FIG. 4 is required to be one circuit for one SLED chip.

(Other Embodiments) The control device of the present invention is shown in FIG.
It is not limited to the configuration of the embodiment. For example, the outputs of the voltage detection unit U1 and the current detection unit U2 are
The digital signal is converted by the D converter, the inverted signal of the digital signal and the image data is input to the one-chip CPU, the cathode resistance R of the light-emitting element is calculated in the CPU, the inversion signal is integrated, and the integrated value and R It is also possible to generate a control signal for extinguishing, which is output to the OR gate G1 by making a comparison with the value of.

Further, although the embodiment of FIG. 4 is composed of a plurality of units, it is also possible to integrate the entire control circuit of FIG. 4 into a single chip to form one unit.

Further, in the above-described embodiment of the present invention, the light emission time is controlled as the control for correcting the variation in the light emission luminance of the light emitting element, but the cathode current of the light emitting element may be controlled.

The present invention is suitable for a device using a plurality of light emitting elements. Therefore, it is suitable not only for the LED (light emitting diode) printer exemplified in the above embodiment but also for display of a matrix type LED display and the like. Further, the present invention can be applied not only to a printer but also to various devices such as a copying machine, a facsimile machine, a ticket issuing machine, etc., which incorporates a printing mechanism. The present invention may be applied to a system including a plurality of devices or an apparatus including one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus. In this case, by reading a storage medium storing a program represented by software for achieving the present invention into the system or the apparatus, the system or the apparatus can enjoy the effects of the present invention. Becomes

[0037]

As described above, according to the present invention,
In controlling the light quantity of the light emitting element array using the PNPN thyristor structure, the cathode resistance of the light emitting element is measured during the light emission of the light emitting element, and the cathode resistance measurement result is fed back to the light emission control signal, thereby each light emitting element. It is possible to approximately correct the brightness variation.

Further, according to the present invention, since the correction control can be performed in real time at the same time as the start of lighting, the work of previously measuring and storing each luminance is unnecessary, and the efficiency of product production is improved. You can

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing a configuration of an SLED used in an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a waveform of a pulse applied to the SLED used in the embodiment of the present invention.

FIG. 3 is a circuit diagram showing an equivalent circuit of an SLED for an electrophotographic printer used in an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a light emission control circuit according to an embodiment of the present invention.

5 is a waveform diagram showing an output waveform of the light emission control circuit of FIG.

[Explanation of symbols]

 G1 OR gate G2 Inversion gate Tr1 Transistor Sr1 Light emitting thyristor U1 Voltage detection unit U2 Current detection unit U3 Logarithmic conversion unit U4 Difference calculation unit U5 Inverse logarithmic conversion unit U6 Comparison unit U7 Integration unit

Claims (15)

[Claims] 1. A light emitting element control device using a PNPN thyristor structure, a light emitting element using the PNPN thyristor structure, a signal generating means for outputting a light emission control signal for controlling light emission of the light emitting element, and the light emitting element. Measuring means for measuring the cathode resistance of the light emitting element, the cathode resistance is measured by the measuring means during light emission of the light emitting element, and the measurement result is fed back to the light emission control signal to control the light emission of the light emitting element. A control device for a light emitting element, comprising: a control means. 2. The measuring means according to claim 1, wherein the measuring means includes a voltage detecting means for detecting a cathode voltage of the light emitting element, a current detecting means for detecting a cathode current of the light emitting element, and a voltage detecting means of the voltage detecting means. Logarithmic conversion means for logarithmically converting the output and the output of the current detection means, difference calculation means for calculating the difference between the outputs of the logarithmic conversion means, and antilogarithmic conversion means for inverse logarithmic conversion of the output of the difference calculation means. And the output of the antilogarithmic conversion means corresponds to the measurement result. 3. The measuring means according to claim 1, wherein the measuring means includes a voltage detecting means for detecting a cathode voltage of the light emitting element, a current detecting means for detecting a cathode current of the light emitting element, and a voltage detecting means of the voltage detecting means. A control device for a light emitting element, comprising: an output and an arithmetic means for calculating a cathode resistance value of the light emitting element from an output of the current detecting means. 4. The control unit according to claim 1, wherein the control unit integrates the light emission control signal, and a comparison unit compares the measurement output of the measurement unit and the output of the integration unit. And a logic unit that suppresses the light emission control signal according to the comparison result of the comparison unit. 5. The control device for a light emitting element according to claim 1, wherein the light emission control signal is an image signal. 6. The light emitting element control device according to claim 1, wherein the light emitting element is a light emitting element array that constitutes an exposure device of an electrophotographic printer. 7. The light-emitting element according to claim 1, wherein the light-emitting element is a light-emitting element array that constitutes a print exposure apparatus of an electronic device having a built-in electrophotographic printing mechanism. Device control device. 8. The control device for a light-emitting element according to claim 7, wherein the electronic device incorporating the electrophotographic printing mechanism is a facsimile device. 9. The light emitting element control device according to claim 1, wherein the light emitting element is a light emitting element array constituting a display device. 10. A method of controlling a light emitting device using a PNPN thyristor structure, wherein the cathode resistance of the light emitting device is controlled during the light emission of the light emitting device by utilizing the fact that the cathode resistance of the light emitting thyristor and the emission brightness are correlated. A method of controlling a light emitting element, comprising: measuring and measuring the cathode resistance and feeding back the result of the measurement to a light emission control signal of the light emitting element to approximately correct the luminance variation of each light emitting element. 11. The measurement step of measuring the cathode resistance of the light emitting element during the light emission of the light emitting element, the measurement result of the measurement step being fed back to the light emission control signal according to claim 10. And a control step of controlling light emission of the light emitting element. 12. The measuring step according to claim 11, wherein the measuring step includes a voltage detecting step of detecting a cathode voltage of the light emitting element, a current detecting step of detecting a cathode current of the light emitting element, and the voltage detecting step. A logarithmic conversion step for performing logarithmic conversion of each detection result, a difference operation step for performing a difference operation for each logarithmic conversion result in the logarithmic conversion step, and an inverse logarithmic conversion step for performing an inverse logarithmic conversion on the operation result in the difference operation step A method for controlling a light-emitting element, comprising: 13. The measuring method according to claim 11, wherein the measuring step includes a voltage detecting step of detecting a cathode voltage of the light emitting element, a current detecting step of detecting a cathode current of the light emitting element, and the voltage detecting step. And a calculation step of calculating a cathode resistance value of the light emitting element from the detection result of the current detection step and the detection result of the current detection step. 14. The control step according to claim 11, wherein the control step compares an integration step of integrating the light emission control signal with a measurement result of the measurement step and an integration result of the integration. A method of controlling a light emitting element, comprising: a comparison step; and a lighting control step of suppressing the light emission control signal based on a comparison result of the comparison step. 15. A storage medium storing the processing procedure of each step according to any one of claims 11 to 14.