JPH07156444A - Light quantity correction type driving circuit of light emitting device array - Google Patents

Abstract

PURPOSE:To equalize light quantity of each light emitting device in a light emitting device array neither by lowering productivity nor by raising a cost. CONSTITUTION:A printing data output part 21 which outputs analog density information as a density data signal DATA, and a correction memory circuit 34 which stores a correction data corresponding to dispersion in light quantity of each light emission device and converts the density data signal DATA to a density conversion data signal MDATA to be outputted, are provided. A data holding circuit which holds the density conversion data signal MDATA, a means outputting an enabling signal ENABLE, an analog voltage generation circuit 26 which generates analog output voltage VR corresponding to the density conversion data signal MDATA, and a group of current setting circuits CS1-CSn which generate a driving current corresponding to the output voltage VR, and supply it to each light emitting device, are provided. A driving current corresponding to the density conversion data signal MDATA can be supplied to each light emitting device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light amount correction type driving circuit for a light emitting element array used as a light source in an optical printer.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, a laser printer, a light emitting diode (hereinafter referred to as "LED").
Say. ) Optical printers such as printers and liquid crystal printers are known. Among them, the LED printer includes a LED head as a light emitting element array formed by linearly arranging LEDs as a plurality of light emitting elements and a converging rod lens array, and the printer head is compact and simplifies the structure. In addition, the alignment of the optical system is easy (see Japanese Utility Model Laid-Open No. 4-130853).

FIG. 2 is a conceptual diagram of a conventional LED printer. In the figure, the print data output unit 11 scans an image sensor (not shown) to read an image such as a character or a figure on a subject such as a document,
While obtaining the analog density information, the analog density information is converted into serial print data for each pixel (one dot), and the print data is converted into a video signal in the LED driving unit 12
Are sequentially output to. Then, when the LED drive unit 12 performs serial / parallel conversion of the print data and outputs parallel print data to the LED array light source unit 13, the LED array light source unit 13 is not shown in the LE.
D is made to selectively emit and extinguish according to print data.

The LED array light source unit 13 comprises an LED array and a converging rod lens array 14, and the LED array monolithically integrates about 64 to 128 LEDs having the same operation characteristics into one chip (module).
And further formed by arranging a plurality of chips linearly. When each LED is caused to emit light in accordance with print data, each light irradiates the surface of the photoconductor drum 16 through the converging rod lens array 14 to expose the photoconductor drum 16. The photosensitive drum 16 is rotated in the direction of arrow A, and is uniformly and evenly charged by the charger 15. Then, when the light from the LED illuminates the surface of the photoconductor drum 16, an electrostatic latent image corresponding to the print data is formed on the photoconductor drum 16. The electrostatic latent image is sent to the developing device 17 as the photosensitive drum 16 rotates, and is developed by the developing device 17 to become a black and white binary toner image. Then, the toner image is transferred to the photosensitive drum 16
Is transferred to a transfer device 18 and is transferred to a sheet 19 by the transfer device 18.

By the way, when an image such as a character or a figure on a subject such as an original is read and the image is printed in black and white binary, a constant voltage is applied to the LED drive section 12. Then, each LE in a light emitting state
At D, a drive current of the same value corresponding to the constant voltage applied to the LED drive unit 12 flows, and each LED emits the same light emission output.

By the way, recently, an optical printer having a printing function corresponding to image images such as photographic data and graphic data and color images has been provided. in this case,
A printer head having a gradation function is used for printing an image in multi-value. Next, a drive circuit of an LED array using a printer head having a gradation function will be described.

FIG. 3 is a block diagram of a conventional LED array drive circuit. In the figure, the print data output unit 21
Is a scanning type or fixed type image sensor 22 for reading an image such as a character or a figure on a subject such as a document.
An A / D converter 23 for converting the analog density information obtained by the image sensor 22 into a digitized density data signal DATA of a plurality of bits (for example, at least 6 bits) in pixel units, and the A / D conversion Density data signal DAT in pixel units digitized by the device 23
It comprises a pixel density data memory 24 for sequentially writing A. Then, the density data signal DATA stored in the pixel density data memory 24 is appropriately output to the LED driving section 20.

The LED driving section 20 has n equal to the number of LED arrays A1 to An in the LED array light source section 27.
It is composed of individual drive circuits DR1 to DRn. Each of the LED arrays A1 to An is composed of one chip and has m LEDs. The circuit configurations of the drive circuits DR1 to DRn are the same. Then, the n driving circuits DR1 to DR1
The DRn are respectively connected in cascade, and the density data signal DAT output from the pixel density data memory 24 during pixel driving is output.
Dedicated register groups (hereinafter referred to as "register groups") RG1 to RGn for storing A, and the respective register groups RG1 to RGn
The concentration data signal DATA stored in the load signal LO
Dedicated latch circuit groups (hereinafter referred to as "latch circuit groups") LT1 to LTn as data holding circuits that hold in pixel units in synchronization with AD, and the respective latch circuit groups LT1 to LT
density data signal DATA held in n is inputted, the concentration data signal corresponding driving current current setting circuits CS1~CSn supplied to the LED to DATA, and the analog voltage V _R on the current setting circuit group CS1~CSn , And has an analog voltage generating circuit 26 for applying a voltage, and is monolithically integrated.

Next, the LED arrays A1 to An having the above structure
The operation of the drive circuits DR1 to DRn will be described. First, in the print data output unit 21, the image sensor 22 reads an image such as a character or a figure on a subject such as a document and outputs analog density information to the A / D converter 23. The A / D converter 23 converts the analog density information into a plurality of bits of digitized density data signal DATA (pixel data D _{0 to} D _{5 in} this case).
To form 64 gray levels. ) And writes the density data signal DATA in the pixel density data memory 24.

Subsequently, the CPU (not shown) reads out the density data signal DATA of the first line in the main scanning direction from the pixel density data memory 24 and synchronizes with the clock CLK to register the registers R0 to R0 of the register groups RG1 to RGn.
Write to R5 in parallel. The register groups RG1 to R
Gn is configured based on the number of LEDs of the LED arrays A1 to An and the number of conversions of the density data signal DATA. In this case, the number of LEDs of each LED array A1 to An is m, and the density data signal DATA is 6 bit data D.
Since each of the register groups RG1 to RGn has _{0 to} D ₅ , each of the register groups RG1 to RGn has an m × 6 matrix configuration.

Since the register groups RG1 to RGn are cascade-connected, the density data signal DATA is sequentially shifted to the register groups RG1 to RGn of the next stage.
When the density data signal DATA of the first line is written in all the register groups RG1 to RGn, the C
A load signal LOAD is output from PU, and the density data signal DATA is held in each latch circuit group LT1 to LTn.

The latch circuit groups LT1 to LTn have a matrix structure of m × 6 like the register groups RG1 to RGn, and each register R0 of the register groups RG1 to RGn.
To R5 and each latch circuit L of the latch circuit groups LT1 to LTn
0 to L5 are associated with each other. Therefore, for example, the output of the register R0 is input only to the latch circuit L0.

By the way, the output of the latch circuit L0~L5 latch circuit group LT1~LTn, for example, the enable signal ENABLE (consisting of bits data E ₀ ~E _5.)
Wired or. Therefore, the outputs of the latch circuit groups LT1 to LTn are unified by the enable signal ENABLE selectively and sequentially input to the respective latch circuits L0 to L5, and the LED current output units described later in the current setting circuit groups CS1 to CSn are integrated. Entered in. In addition, Syn
c is a synchronizing signal.

Next, the current setting circuit groups CS1 to CSn
Will be described. The current setting circuit groups CS1 to C
Sn has m current setting circuits corresponding to the LEDs of the LED arrays A1 to An. FIG. 4 is a diagram showing a conventional current setting circuit. In the figure, the analog voltage generating circuit 26 is connected to the non-inverting input terminal (+) of the operational amplifier OP, and the output voltage V _R of the analog voltage generating circuit 26 is input to the non-inverting input terminal (+). The output terminal of the operational amplifier OP is connected to the source of an N-channel MOS transistor (hereinafter referred to as “NMOS transistor”) Q1, the gate of the NMOS transistor Q1 is used as a power supply _VDD , and the drain is a P-channel MOS transistor. (Hereinafter referred to as "PMOS transistor".) Q
2 gates respectively connected. The source of the PMOS transistor Q2 is connected to the power supply V _DD , the drain is connected to the inverting input terminal (−) of the operational amplifier OP, and is connected to the ground via the resistor R.

In this way, the NMOS transistor Q1,
The PMOS transistor Q2 and the resistor R form a feedback circuit 28 for feeding back the output voltage V _O of the operational amplifier OP to the inverting input terminal (−). Further, between the output terminal of the operational amplifier OP and the power supply V _DD, an inverter Q3 composed of a complementary connected PMOS transistor Q3a and NMOS transistor Q3b is connected. In the inverter Q3, a gate common connection point which is its input terminal is connected to the latch circuits L0 to L5, a drain common connection point which is an output terminal is connected to the gate of the PMOS transistor Q4, and the latch circuits L0 to L are connected.
P based on the density data signal DATA as the output of 5
The MOS transistor Q4 is turned on / off. The source of the PMOS transistor Q4 is the power source V
_The drain is connected to _DD and the output terminal OUT is connected.

As described above, the inverter Q3 and the PMOS
The current output unit 29 is composed of the transistor Q4.
It The output terminal OUT is the anode of the LED.
The cathode of the LED is connected to ground. Before
In the current setting circuit with the above configuration, an analog voltage generation circuit
Output voltage V from 26_RIs the non-inverting input of the operational amplifier OP
The output voltage V of the operational amplifier OP is connected to the terminal (+). _OIs an increase in calculation
Input to the inverting input terminal (-) of the width device OP
The non-inverting input terminal (+) and the inverting input terminal.
Output voltage V so that each voltage of (-) becomes equal_OIs controlled
To be done. By this operation, the resistance R of the feedback circuit 28 is
Current I flowing through_RBecomes as shown in the following equation (1).

I _R = V _R / R (1) At this time, the gate of the NMOS transistor Q1 has a power source V
It is on because it is connected to _DD . Therefore,
The gate voltage V _G of the PMOS transistor Q2 becomes equal to the output voltage V _O, and the gate-source voltage V _GS of the PMOS transistor Q2 becomes V _GS = V _DD −V _O. Here, the current flowing through the PMOS transistor Q2 is equal to the current I _R flowing through the resistor R, and has a relationship that it increases as the gate-source voltage V _GS increases, so that the gate voltage V _G (= V
_O ) to change the gate of the PMOS transistor Q2
The source-to-source voltage V _GS can be controlled.

The output voltage V _O of the operational amplifier OP is
It also serves as a control voltage for operating the current output unit 29. That is, when the inverter Q3 is turned on by the density data signal DATA of the latch circuits L0 to L5 which is the control signal of each LED, the LED drive current I _OUT flows through the PMOS transistor Q4. in this case,
The drive current I _{OUT of} each LED is the PMOS transistor Q2.
So that it is an integer multiple of the current (= I _R ) flowing in the
The channel width of the transistors Q2 and Q4 is set.

FIG. 5 shows the output voltage of the analog voltage generating circuit.
It is a relationship diagram of a drive current. The horizontal axis of the figure indicates the output voltage V
_RIs the drive current I on the vertical axis_OUTIs taken. As shown in the figure
Output voltage V of the analog voltage generation circuit 26 (FIG. 3)
_RAnd LED drive current I_OUTIs a linear relationship. Well
Further, the density data held in the latch circuits L0 to L5
Bit data D of signal DATA₀~ D_FiveNumber of (this place
In the case of 6), the output voltage V_RAnd divide it evenly
The obtained value V_R1, V_R2,,, V _R6(However, V_R1<
V_R6) Drive current I corresponding to_OUTIs supplied to each LED
I am trying.

When the enable signal ENABLE is generated for each of the latch circuits L0 to L5 and the enable signal ENABLE is input to the latch circuits L0 to L5, the density data signal DATA held in the latch circuits L0 to L5. Are sequentially output from the upper bit data D ₅ . In this case, the CPU causes the enable signal ENABL
A synchronization signal Sync is generated in synchronization with E and output to the analog voltage generation circuit 26. The analog voltage generation circuit 26 sequentially outputs an analog output voltage V _R corresponding to the density data signal DATA from the value V _R6 to the value V _R1 in synchronization with the synchronization signal Sync.

As described above, the latch circuit groups LT1 to LT
By a series of operations by the Tn and analog voltage generation circuit 26, the drive current I _OUT supplied to each LED can be made different for each pixel. Therefore, when the LEDs are driven all at once, the light emission output can be made different for each LED. As a result, the photosensitive drum 16 (FIG. 2)
Or 6 on any recording medium by the drive circuits DR1 to DRn
An electrostatic latent image having a pixel density of four gradation levels can be formed.

[0022]

However, in the above-mentioned conventional LED array driving circuit, the LE circuit is difficult to manufacture.
The operating characteristics of the LEDs of the D arrays A1 to An are different, and normally, in each of the LED arrays A1 to An of one chip, each LE is
Since there is a variation of ± 15 to 20 [%] in the light amount of D, the print density at each gradation level also varies, and the image quality deteriorates.

In particular, as the number of gradations increases, the print density at the same gradation level tends to vary,
Image quality deteriorates. Therefore, although LED manufacturing techniques are improved or LEDs having the same operating characteristics are selected, the yield is deteriorated by that amount, the productivity is reduced, and the cost is increased.

The present invention solves the problems of the conventional drive circuit for the LED array, and reduces the light amount of each light emitting element in the light emitting element array without lowering the productivity or increasing the cost. It is an object of the present invention to provide a light amount correction type drive circuit for a light emitting element array that can be equalized.

[0025]

Therefore, in the light amount correction type driving circuit of the light emitting element array of the present invention, the analog density information obtained by reading the image of the subject is digitized pixel by pixel to obtain a density data signal. A print data output unit for sequentially outputting the density data signal, correction data corresponding to the variation in the light amount of each light emitting element, and a correction for converting the density data signal into a density conversion data signal for output. And a memory circuit.

A data holding circuit for holding the density conversion data signal in units of pixels, a means for outputting an enable signal, and density conversion data held in the data holding circuit in synchronization with the output timing of the enable signal. An analog voltage generating circuit for generating an analog output voltage corresponding to the signal, and a drive current corresponding to the output voltage generated by the analog voltage generating circuit,
And a current setting circuit group for supplying the drive current to each light emitting element.

In the light amount correction type drive circuit for another light emitting element array of the present invention, analog density information obtained by reading an image of a subject is digitized pixel by pixel to obtain a density data signal, and the density data signal is obtained. A print data output unit for sequentially outputting and a correction memory circuit for storing the correction data corresponding to the variation of the light amount for each light emitting element and for converting the density data signal into a density conversion data signal and outputting the converted density data signal.

Then, a data holding circuit for holding the density converted data signal in pixel units, means for outputting an enable signal corresponding to the density converted data signal held in the data holding circuit, and output of the enable signal. A current setting circuit group that generates a drive current for a light emission time corresponding to the enable time in synchronization with the timing and supplies the drive current to each light emitting element.

[0029]

According to the present invention, as described above, in the light amount correction type driving circuit of the light emitting element array, the analog density information obtained by reading the image of the object is digitized pixel by pixel to form a density data signal, A print data output unit that sequentially outputs the density data signal, and a correction memory circuit that stores the correction data corresponding to the variation in the light amount of each light emitting element and that converts the density data signal into a density conversion data signal and outputs the density conversion data signal. Have and.

Therefore, the density data signal output from the print data output unit is corrected in accordance with the variation in the light amount of each light emitting element, and converted into the density conversion data signal in the correction memory circuit. A data holding circuit that holds the density converted data signal in units of pixels, a unit that outputs an enable signal, and a density converted data signal that is held in the data holding circuit are synchronized with the output timing of the enable signal. An analog voltage generating circuit for generating an analog output voltage, and a current setting circuit group for generating a drive current corresponding to the output voltage generated by the analog voltage generating circuit and supplying the drive current to each light emitting element. Have.

Therefore, the drive current corresponding to the density converted data signal can be supplied to each light emitting element.
In a light amount correction type driving circuit for another light emitting element array of the present invention, analog density information obtained by reading an image of a subject is digitized pixel by pixel to generate a density data signal, and the density data signal is sequentially output. A print data output unit and a correction memory circuit that stores correction data corresponding to variations in the light amount of each light emitting element and that converts the density data signal into a density conversion data signal and outputs the density conversion data signal.

Therefore, the density data signal output from the print data output unit is corrected in accordance with the variation in the light amount of each light emitting element, and converted into the density conversion data signal in the correction memory circuit. A data holding circuit that holds the density converted data signal in units of pixels, a unit that outputs an enable signal corresponding to the density converted data signal held in the data holding circuit, and a synchronization with the output timing of the enable signal And a drive current is generated for a light emission time corresponding to the enable time, and the drive current is supplied to each light emitting element.

Therefore, the drive current can be supplied to each light emitting element for the light emission time corresponding to the density conversion data signal.

[0034]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of a light amount correction type driving circuit for a light emitting element array according to a first embodiment of the present invention. In the figure, a print data output unit 21 displays a scanning or fixed image sensor 22 for reading an image of a character, a figure, or the like on a subject such as a document, and analog density information obtained by the image sensor 22 in pixel units. A to convert into a plurality of bits (for example, at least 6 bits) of digitized density data signal DATA
The D / D converter 23 and the pixel density data memory 24 for sequentially writing the pixel-based density data signal DATA digitized by the A / D converter 23. Then, the density data signal DATA stored in the pixel density data memory 24 is appropriately output to the LED driving section 20.

The LED drive section 20 includes an LED array A as a light emitting element array in the LED array light source section 27.
The number of drive circuits DR1 to DRn is equal to the number of drive circuits 1 to An. Each of the LED arrays A1 to An is composed of one chip, and each has m LEDs as light emitting elements. The circuit configurations of the drive circuits DR1 to DRn are the same.

The n driving circuits DR1 to DRn are respectively connected in cascade, and register groups RG1 to RGn for storing the density data signal DATA output from the pixel density data memory 24 in pixel units, and the respective register groups RG1.
To latching circuit groups LT1 to LTn as a data holding circuit that holds the density data signal DATA stored in RGn in synchronization with the load signal LOAD in pixel units, and the density data signals held in the respective latch circuit groups LT1 to LTn D
The current setting circuit group CS1 to which ATA is input and which supplies the drive current corresponding to the density data signal DATA to the LED
The analog voltage generating circuit 26 for applying the output voltage V _R to CSn and the current setting circuit groups CS1 to CSn is included and monolithically integrated.

Next, the LED arrays A1 to An having the above-mentioned structure.
The operation of the drive circuits DR1 to DRn will be described. First, in the print data output unit 21, the image sensor 22 reads an image such as a character or a figure on a subject such as a document and outputs analog density information to the A / D converter 23. The A / D converter 23 converts the analog density information into a plurality of bits of digitized density data signal DATA (pixel data D _{0 to} D _{5 in} this case).
To form 64 gray levels. ) And writes the density data signal DATA in the pixel density data memory 24.

Subsequently, the CPU (not shown) reads the density data signal DATA of the first line in the main scanning direction from the pixel density data memory 24 and synchronizes with the clock CLK to register each of the registers R0 to Rn of the register groups RG1 to RGn.
Write to R5 in parallel. The register groups RG1 to R
Gn is configured based on the number of LEDs of the LED arrays A1 to An and the number of conversions of the density data signal DATA. In the present embodiment, the LEDs of each LED array A1 to An
Is m and the density data signal DATA is composed of 6 bit data D _{0 to} D ₅ , each register group RG1
˜RGn has an m × 6 matrix configuration.

In this case, the register groups RG1 to RGn
Are connected in cascade, the density data signal DATA is sequentially shifted to the register groups RG1 to RGn in the next stage. Then, all the register groups RG1 to RGn
When the density data signal DATA of the first line is written in, the load signal LOAD is output from the CPU, and the density data signal DATA is supplied to each of the latch circuit groups LT1 to LT.
It is held at Tn.

The latch circuit groups LT1 to LTn have a matrix structure of m × 6 like the register groups RG1 to RGn, and each register R0 of the register groups RG1 to RGn.
To R5 and each latch circuit L of the latch circuit groups LT1 to LTn
0 to L5 are associated with each other. Therefore, for example, the output of the register R0 is input only to the latch circuit L0.

By the way, the latch circuit groups LT1 to LTn
The outputs of the latch circuits L0 to L5 are, for example, output timings.
Enable signal ENABLE (bit data
E ₀~ E_FiveConsists of. ) Is wired or
It Therefore, the outputs of the latch circuit groups LT1 to LTn
Are selectively sequentially input to the latch circuits L0 to L5.
Current is unified by enable signal ENABLE
LED current output unit 29 in the setting circuit groups CS1 to CSn
(See FIG. 4).

When the enable signal ENABLE is generated for each of the latch circuits L0 to L5 and the enable signal ENABLE is input to the latch circuits L0 to L5, the density data signal DATA held in the latch circuits L0 to L5. Are sequentially output from the upper bit data D ₅ . In this case, the CPU causes the enable signal ENABL
A synchronization signal Sync is generated in synchronization with E and output to the analog voltage generation circuit 26. The analog voltage generating circuit 26 sequentially outputs an analog output voltage V _R corresponding to the concentration data signal DATA from the value V _R6 (see FIG. 5) to the value V _R1 in synchronization with the synchronization signal Sync.

Thus, the latch circuit groups LT1 to LT
By a series of operations by the Tn and analog voltage generation circuit 26, the drive current I _OUT supplied to each LED can be made different for each pixel. Therefore, when the LEDs are driven all at once, the light emission output can be made different for each LED. As a result, the drive circuits DR1 to DRn can form an electrostatic latent image having a pixel density of 64 gradation levels on the photosensitive drum 16 (see FIG. 2) or an arbitrary recording medium.

By the way, there is a variation in the light quantity of each LED of the LED arrays A1 to An. That is, when the drive current I _OUT generated based on the density data signal DATA is supplied to the LEDs as they are, the light emission output of each LED is different at the same gradation level. Therefore, the print density varies at the same gradation level, and the image quality deteriorates.

Therefore, a correction memory circuit 34 is connected to the pixel density data memory 24 and the LED driving section 20, and based on the density data signal DATA read from the pixel density data memory 24, from the bit data P _{ix0 to} P _ix5. The density conversion data signal MDATA is generated and the density conversion data signal MDATA is output to the LED drive unit 20.

DTP is a synchronization signal (DATA TOP PULSE) for output timing, and BUSY is a busy signal. Here, the relationship between the light emission output of each LED in the LED arrays A1 to An and the exposure energy in the photoconductor drum 16 will be described. FIG. 6 is a relationship diagram between the light emission output of the LED and the exposure energy of the photosensitive drum in the first embodiment of the present invention. The horizontal axis of the figure shows the LED
Drive current I _OUT supplied to the photosensitive drum 1 on the vertical axis.
The exposure energy E at 6 (see FIG. 2) is taken.

As shown in the figure, the drive current I _OUT and the exposure energy E are in a proportional relationship. For example, when the light emission output P is P _typ when the drive current I _OUT is set to the reference value I _typ , the exposure energy E is set. The reference value of is E _typ . By the way, in the one-chip LED arrays A1 to An (FIG. 1), there is a variation in the light amount of each LED, and the variation in each light amount is due to the variation in the light emission output P.

Therefore, each LED in one chip
Each P _max the maximum value and the minimum value of the emission output P of, P
_{If the} value is _min , the drive current I _OUT of the reference value I _typ is set to the LED
The exposure energy E when it is supplied to each LED is different for each LED, and the maximum and minimum values of the exposure energy E are respectively E
It becomes _max and E _min . Therefore, when printing is performed at least at the same gradation level, the spread of the maximum value P _max and the minimum value P _min of the light emission output P is reduced, and the drive current I as shown by arrows A ₁ and A _{2 in the} figure is reduced. By changing _OUT , the exposure energy E can be set to the reference value E _typ . That is, for example, the light emission output P is the maximum value P _max.
When the minimum value I _min of the drive current I _OUT is supplied to the LED and the maximum value I _max of the drive current I _OUT is supplied to the LED whose emission output P is the minimum value P _min , the exposure energy E is obtained.
Can be set to the reference value E _typ .

In the present embodiment, the density data signal DATA is generated in correspondence with the light emission output P of each LED, and the drive current I _OUT is changed to change the LED.
The amount of light is corrected. It is generally known that the spread of the maximum value E _max and the minimum value E _min of the exposure energy E may be set to ± 5% or less in order to make the variation of the print density inconspicuous. Therefore, the correction range of the density data signal DATA can be set wider by this amount.

Next, the correction memory circuit 34 will be described. FIG. 7 is a block diagram of a correction memory circuit according to the first embodiment of the present invention. As shown in the figure, the correction memory circuit 34 is an EPROM (hereinafter referred to as “memory”) 3.
5, an address counter 36 and a latch unit 37.
Then, the memory 35 stores a correction conversion table (not shown) for correcting the light amount of each LED (not shown) to eliminate variations. The correction conversion table is composed of density conversion data values as correction data, and the density conversion data values are stored in advance at the L level at each gradation level.
It is set corresponding to the variation in the light amount for each ED.

The address counter 36 outputs an address to the memory 35 to select the density conversion data value. Then, the selected density conversion data value is passed through the latch unit 37 to the LED drive unit 2 as a density conversion data signal MDATA composed of bit data P _{ix0 to} P _ix5.
0 (FIG. 1) is output. Note that DTP is a synchronization signal of output timing, and BUSY is a busy signal. DATA (D _{0 to} D ₅ ) is a density data signal, I / O
Input and output _{ports, A 6 ~A k, A 0} ~A 5 is the bit data of the address.

Next, the operation of the correction memory circuit 34 having the above configuration will be described with reference to FIG. FIG. 8 is a diagram showing a memory data map of the light amount correction type drive circuit for the light emitting element array according to the first embodiment of the present invention. First, the print data output unit 21 (FIG. 1) outputs the density data signal DATA to the correction memory circuit 34, and the synchronization signal DTP and the busy signal BUSY are output to the correction memory circuit 3.
4 is output.

The synchronizing signal DTP is the density data signal D.
Only one pulse is output immediately before ATA is output, and the output values A _{6 to} A _k (k: any integer) of the address counter 36 are initialized. Further, the busy signal BUSY is output at the same time as the density data signal DATA, and the address counter 36 starts counting. The address counter 3
A clock CLK (not shown) for determining the operation speed of the correction memory circuit 34 is input to the latch circuit 6 and the latch unit 37.

By the way, the density data signal DATA is
6-bit bit data D₀~ D_FiveConsists of, parallel
Is input to the correction memory circuit 34 and is directly stored in the memory 35.
Will be the address of. Therefore, the address of the memory 35
6-bit data A ₀~ A_FiveConsists of. There
Then, as shown in the figure, the bits of the density data signal DATA
Data D₀~ D_Five0 to 63 gradation level represented by
Bell and the address values 0 to 63 (HEX change) of the memory 35.
Substitution value: 0h to 3Fh) correspond one-to-one, and one of them
When the address value of is selected, the light intensity of the LED (not shown)
Density conversion data value for correction (bit data b₀~
b_Five) Is obtained, and the density conversion data value is the density conversion data
Is output from the correction memory circuit 34 as a signal MDATA.
It

The address value selected in the initial state of the correction memory circuit 34 corresponds to the LED of the first dot. And the address value of the LED after the second dot is
The output values A _{6 to} A _k of the address counter 36 are sequentially selected. That is, when the address value is selected by the density data signal DATA, the density conversion data value stored at the address of the address value is read. In this case, the LED area in the memory 35 is determined by the count value of the address counter 36.

In this way, the density conversion data signal MDATA output from the correction memory circuit 34 is transferred to the drive circuit D.
By inputting into R1 to DRn, the drive current I _OUT (see FIG. 4) corresponding to the variation in the light amount of each LED can be supplied to each LED, and the exposure energy E can be set to the reference value E _typ. . Therefore, variations in print density at the same gradation level do not occur, and image quality can be improved.

Further, since it is not necessary to improve the LED manufacturing technique or to select the LEDs having the same operating characteristics, the yield can be improved accordingly, the productivity can be improved, and the cost can be reduced. You can Further, since the correction memory circuit 34 can be monolithically integrated, a printer head (not shown) can be downsized.

Next, a second embodiment of the present invention will be described. FIG. 9 is a block diagram of a light amount correction type driving circuit for a light emitting element array according to the second embodiment of the present invention, and FIG. 10 is a relation between the light emission output of the LED and the exposure energy of the photosensitive drum in the second embodiment of the present invention. FIG. 11 and FIG. 11 are time charts of the enable signal in the second embodiment of the present invention. The horizontal axis of FIG. 10 represents the light emission time T of the LED, and the vertical axis represents the exposure energy E of the photosensitive drum 16 (see FIG. 2). Further, the same parts as those in FIG.

In this embodiment, the print data output unit 2
Density data signal DAT sequentially output from 1 in pixel units
A is input to the correction memory circuit 38 and converted into the density conversion data signal MDATA in the correction memory circuit 38. The correction of the light amount of the LED in this embodiment is performed based on the following equation (2). That is, when the light emission output of the LED is P and the light emission time is T, the exposure energy E is represented by the following equation (2).

E = P · T (2) That is, as shown in FIG. 10, the light emission time T and the exposure energy E are in a proportional relationship. For example, light emission when the light emission time T is set to a reference value T _typ When the output P is P _typ , the reference value of the exposure energy E is E _typ . By the way, LED
In each of the arrays A1 to An, there is a variation in the light amount of each LED within one chip, and the variation in each light amount causes a variation in the light emission output P.

Therefore, each LED in one chip
Each P _max the maximum value and the minimum value of the emission output P of, P
_If it is set to _min , the exposure energy E when the LED emits light for the reference value T _typ of the light emission time T is different for each LED, and the maximum value and the minimum value of the exposure energy E are respectively E.
It becomes _max and E _min . Therefore, when printing is performed at least at the same gradation level, the spread of the maximum value P _max and the minimum value P _min of the light emission output P is reduced, and the light emission time T is as shown by arrows B ₁ and B _{2 in the} figure. The exposure energy E can be set to the reference value E _typ by changing. That is, for example, emission output P is caused to emit light by the minimum value T _min of the LED light emission time T is the maximum value P _max, the LED light emission output P is the minimum value P _min by the maximum value T _max of the light emission time T emission Then, the exposure energy E can be set to the reference value E _typ .

In this embodiment, the density data signal DATA is generated corresponding to the light emission output P of each LED, and the light emission time T is changed to correct the light amount of the LED. It is generally known that the spread of the maximum value E _max and the minimum value E _min of the exposure energy E may be set to ± 5% or less in order to make the variation of the print density inconspicuous. Therefore, the correction range of the density data signal DATA can be set wider by this amount.

The correction memory circuit 38 includes the memory 35 (FIG. 7), the address counter 36 and the latch section 3.
It consists of 7. The memory 35 stores a correction conversion table (not shown) for correcting the light amount of each LED to eliminate the variation. The correction conversion table is composed of density conversion data values as correction data composed of bit data P _{ix0 to} P _ix5, and the density conversion data values are set in advance so as to correspond to variations in the light amount of each LED at each gradation level. It

In this case, in order to output the density conversion data signal MDATA held in the latch circuit groups LT1 to LTn to the current setting circuit groups CS1 to CSn, a CPU (not shown) synchronizes with the load signal LOAD to generate 6 bits. Enable signal ENA consisting of the bit data E _{0 to} E _{5 of}
BLE (ENABLE0 to ENABLE5) is output to the latch circuit groups LT1 to LTn.

The enable signal ENABLE corresponds to the output of the density conversion data signal MDATA, as shown in FIG.
Different enable times t1 to t6
Only the pulse can be generated. For example, the enable time t1 is set for each of the bit data P _{ix0 to} P _ix5.
~ T6 is associated. In this way, the enable signal ENABLE for generating pulses of different enable times t1 to t6 is output, and in synchronization with the output timing of the enable signal ENABLE,
The density conversion data signal MDATA is the current setting circuit group CS1.
To CSn are sequentially output. On the other hand, each LED of the LED array Al-An, the driving current I _OUT of the constant current at a constant voltage (the output voltage V _R) is supplied by a constant voltage generating circuit 39.

Therefore, each LED can be made to emit light for the light emission time T corresponding to the density conversion data signal MDATA, and printing can be performed at 64 gradation levels. Incidentally, in the first and second embodiments,
Although the analog density information is converted into the 6-bit density data signal DATA on a pixel-by-pixel basis, it may be converted into the density data signal DATA having a bit number other than 6 bits.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0068]

As described in detail above, according to the present invention, in the light amount correction type driving circuit of the light emitting element array, the analog density information obtained by reading the image of the object is digitized in pixel units. As a density data signal, a print data output section for sequentially outputting the density data signal, and correction data corresponding to variations in the light amount of each light emitting element are stored, and the density data signal is converted into a density conversion data signal. And a correction memory circuit for outputting.

Then, a data holding circuit for holding the density converted data signal in pixel units, a means for outputting an enable signal, and the density converted data held in the data holding circuit in synchronization with the output timing of the enable signal. An analog voltage generating circuit for generating an analog output voltage corresponding to the signal, and a drive current corresponding to the output voltage generated by the analog voltage generating circuit,
And a current setting circuit group for supplying the drive current to each light emitting element.

Therefore, the drive current corresponding to the density converted data signal can be supplied to each light emitting element.
As a result, even if the operating characteristics of the respective light emitting elements are different, there is no variation in the print density at each gradation level, and the image quality can be improved.

Further, by improving the manufacturing technique of the light emitting device,
Since it is not necessary to select light emitting elements having the same operating characteristics, the yield can be improved accordingly, the productivity can be improved, and the cost can be reduced. Further, since the correction memory circuit can be monolithically integrated, the printer head can be downsized.
In a light amount correction type driving circuit for another light emitting element array of the present invention, analog density information obtained by reading an image of a subject is digitized pixel by pixel to generate a density data signal, and the density data signal is sequentially output. A print data output unit and a correction memory circuit that stores correction data corresponding to variations in the light amount of each light emitting element and that converts the density data signal into a density conversion data signal and outputs the density conversion data signal.

Then, a data holding circuit for holding the density converted data signal in pixel units, a means for outputting an enable signal corresponding to the density converted data signal held in the data holding circuit, and an output of the enable signal. A current setting circuit group that generates a drive current for a light emission time corresponding to the enable time in synchronization with the timing and supplies the drive current to each light emitting element.

Therefore, the drive current can be supplied to each light emitting element for the light emission time corresponding to the density conversion data signal. As a result, even if the operating characteristics of the respective light emitting elements are different, there is no variation in the print density at each gradation level, and the image quality can be improved.

Further, by improving the manufacturing technique of the light emitting device,
Since it is not necessary to select light emitting elements having the same operating characteristics, the yield can be improved accordingly, the productivity can be improved, and the cost can be reduced. Further, since the correction memory circuit can be monolithically integrated, the printer head can be downsized.

[Brief description of drawings]

FIG. 1 is a block diagram of a light amount correction type drive circuit for a light emitting element array according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram of a conventional LED printer.

FIG. 3 is a block diagram of a conventional LED array drive circuit.

FIG. 4 is a diagram showing a conventional current setting circuit.

FIG. 5 is a relationship diagram between an output voltage and a drive current of an analog voltage generation circuit.

FIG. 6 is a relationship diagram between the light emission output of the LED and the exposure energy of the photosensitive drum in the first embodiment of the present invention.

FIG. 7 is a block diagram of a correction memory circuit according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a memory data map of a light amount correction type drive circuit for the light emitting element array in the first embodiment of the present invention.

FIG. 9 is a block diagram of a light amount correction type drive circuit for a light emitting element array according to a second embodiment of the present invention.

FIG. 10 is a relationship diagram between the light emission output of the LED and the exposure energy of the photosensitive drum in the second embodiment of the present invention.

FIG. 11 is a time chart of an enable signal in the second embodiment of the present invention.

[Explanation of symbols]

21 print data output section 26 analog voltage generation circuit 34, 38 correction memory circuit A1 to An LED array LT1 to LTn latch circuit group CS1 to CSn current setting circuit group RG1 to RGn register group DATA density data signal MDATA density conversion data signal ENABLE enable signal t1~t6 enable time V _R output voltage I _OUT drive current

Front Page Continuation (72) Inventor Mitsuhiko Ogihara 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (2)

[Claims] 1. A print data output section for digitizing analog density information obtained by reading an image of a subject in pixel units to form a density data signal, and sequentially outputting the density data signal, and (b). In addition to storing the correction data corresponding to the variation in the light amount of each light emitting element,
A correction memory circuit for converting the density data signal into a density conversion data signal and outputting the same; (c) a data holding circuit for holding the density conversion data signal in pixel units; and (d) means for outputting an enable signal, (E) an analog voltage generating circuit that generates an analog output voltage corresponding to the density conversion data signal held in the data holding circuit in synchronization with the output timing of the enable signal; and (f) by the analog voltage generating circuit. A light amount correction type drive circuit for a light emitting element array, comprising: a current setting circuit group for generating a drive current corresponding to the generated output voltage and supplying the drive current to each light emitting element. 2. (a) A print data output section which digitizes analog density information obtained by reading an image of a subject in pixel units to form a density data signal, and sequentially outputs the density data signal, and (b). In addition to storing the correction data corresponding to the variation in the light amount of each light emitting element,
A correction memory circuit for converting the density data signal into a density conversion data signal and outputting the same, (c) a data holding circuit for holding the density conversion data signal in pixel units, and (d) a data holding circuit. A means for outputting an enable signal corresponding to the density conversion data signal; and (e) synchronizing with the output timing of the enable signal, a drive current is generated for a light emission time corresponding to the enable time, and the drive current is emitted for each light emission. A light amount correction type drive circuit for a light emitting element array, comprising: a current setting circuit group supplied to the element.