JP2910103B2 - Image recording method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording method and apparatus for reproducing a halftone image using a laser printer or the like, and more particularly, to a method for performing halftone modulation by performing light quantity modulation of a semiconductor laser. The present invention relates to an image recording method and an apparatus effective for reproducing an image.

[Conventional technology]

Generally, a laser printer reproduces a halftone image using a dither matrix method (a so-called area gradation method) in which one pixel is composed of a plurality of dots, or a laser output modulation method in which a laser output is made variable for each pixel. It has been known.

In the former type, as the number of dots constituting one pixel increases, the gradation can be increased,
Conversely, since the problem of lowering the resolution arises, the latter method is usually adopted when there is a request to increase the resolution.

In this case, as the latter laser output modulation method, a pulse width modulation method for varying the laser lighting time in one pixel is mainly employed, but as another method, a light amount modulation method for modulating the laser light amount is used. A prior art of this type has also been provided. As this type of prior art, for example, an output from a gas laser or the like is fixed, and an acousto-optic modulator (hereinafter referred to as an AO modulator) or an electro-optic modulator ( An EO modulator is known, which modulates the amount of laser light indirectly (see Japanese Patent Application Laid-Open No. 63-273832).

[Problems to be solved by the invention]

By the way, as this kind of light quantity modulation method, there is a technical problem that the gas laser, the AO modulator, and the EO modulator themselves are not only expensive but also because the size of the device is large, it does not meet the demand for miniaturization.

In order to solve this kind of technical problem, attention has been focused on a semiconductor laser which can be easily adopted as a small light source, and there is an increasing demand for directly modulating the light amount of the semiconductor laser itself.

Therefore, focusing on the forward current-light output characteristic, which is considered important in performing light quantity modulation, among the characteristics of the semiconductor laser, as shown in FIG. 42, the forward current I (hereinafter referred to as the drive current I) increases. with in the optical output P begins to increase from a certain threshold current I _th rapidly, continue to increase at a constant rate with respect to increase in the subsequent drive current I. Up to the rated output, this slope η =
dp / dI (differential slope efficiency) is substantially constant.

Therefore, if the drive current I is appropriately modulated in accordance with the density level of the image data within a certain range of the differential slope efficiency η, an optical output corresponding to the density level of the image data can be obtained. is there.

However, the light output of the semiconductor laser easily fluctuates due to a change in the ambient temperature and the heat generated by the semiconductor laser itself.

That is, when the temperature T rises, the threshold current I _th of the semiconductor laser rises exponentially as shown in the following equation (I), so that the optical output of the semiconductor laser becomes the threshold current as shown in FIG. This is because the current I _th easily changes due to a large change depending on the ambient temperature.

I _th = KI _th0 exp (T / T ₀ ) (1) where K is a proportional constant, and I _th0 is a threshold current at the temperature T ₀ .

Therefore, it is extremely difficult for a semiconductor laser to obtain a constant light output according to the density level of image data, and this is an important technical problem in performing light quantity modulation of the semiconductor laser.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described technical problem, and an image recording method capable of modulating a light amount of a semiconductor laser so as to obtain a constant light output according to a density level of image data. Methods and apparatus are provided.

[Means for solving the problem]

That is, the image recording method according to the present invention modulates the light amount from the semiconductor laser 1 according to the density level of the multi-tone image data DT of each pixel, as shown in FIG.
An image recording method for forming a latent image corresponding to each pixel on the photoreceptor 2 and visualizing each latent image with the developing means 3 is assumed. A drive current modulation area determining step (step) of determining a drive current modulation area by correcting a temperature variation of the threshold current I _th of 1
And the multi-gradation image data DT within the determined drive current modulation area.
And a driving current generating step (step) of generating a driving current of the semiconductor laser 1 according to the concentration level of the semiconductor laser 1.

In such a method invention, the drive current modulation area may cover the entire drive current of the semiconductor laser 1, but since there is almost no light output in the area within the threshold current I _th of the semiconductor laser 1, There is almost no light output for the multi-gradation image data DT having a low density gradation number, and the invalid bit is set for the multi-gradation image data having a low density gradation number. Becomes narrower. Therefore, from the viewpoint of reducing the number of invalid bits of the multi-tone image data DT, it is preferable to superimpose an appropriate bias current _IBIAS and use a certain range of the differential slope efficiency η as the drive current modulation area. .

As a setting point of the bias current _IBIAS , from the viewpoint of reliably modulating the drive current in a region where the differential slope efficiency η is constant, the threshold current I _th level or the level immediately before the threshold current I _th level is set. It is preferable to set the bias current I _BIAS ,
In the present method invention sets the bias current I _BIAS immediately before the vicinity level of the threshold current I _th, the bias current I _BIAS
At the set point, the semiconductor laser is kept in a spontaneous emission state without oscillating.

Further, in a first mode (first apparatus invention) of the image recording apparatus according to the present invention, as shown in FIG. 1 (b), a semiconductor device according to the density level of multi-tone image data DT of each pixel. An image recording apparatus that modulates the amount of light from the laser 1 to form a latent image corresponding to each pixel on the photoreceptor 2 and visualizes each latent image by the developing unit 3 is assumed. The full-power driving current value corresponding to the full power is set to the semiconductor laser 1
And power control means (4) for intermittently detected during the non-scanning operation, a fixed bias current source for setting the bias current I _BIAS to the minimum change value level or immediately before the vicinity level of the threshold current I _th of the semiconductor laser 1 is fixedly 5 Between the full power drive current value and the fixed bias current _IBIAS as a drive current modulation area, and a drive current corresponding to the density level of the multi-tone image data DT is determined in the drive current modulation area. And a drive current modulating means 6.

Further, as shown in FIG. 1 (c), a second aspect of the image recording apparatus according to the present invention (second apparatus invention) is a semiconductor device according to the density level of the multi-tone image data DT of each pixel. An image recording apparatus that modulates the amount of light from the laser 1 to form a latent image corresponding to each pixel on the photoreceptor 2 and visualizes each latent image by the developing unit 3 is assumed. A power control means for intermittently detecting a drive current value corresponding to a predetermined power during a non-scanning operation of the semiconductor laser; and a power control means for controlling the semiconductor laser based on the predetermined drive current value detected by the power control means. a bias current changing means 8 for changing the bias current I _bIAS is set to the threshold current I _th level or immediately before the vicinity of level, to determine the constant region as a drive current modulation range from the variable bias current I _bIAS, the drive current modulation In the area Drive current modulation means 9 for determining a driving current corresponding to the density level of the gradation image data DT
It is provided with.

Further, a third mode of the image recording apparatus according to the present invention (third apparatus invention) is, as shown in FIG. 1 (d), a semiconductor device according to the density level of the multi-tone image data DT of each pixel. An image recording apparatus that modulates the amount of light from the laser 1 to form a latent image corresponding to each pixel on the photoreceptor 2 and visualizes each latent image by the developing unit 3 is assumed. and laser temperature control means 10 for controlling the temperature to a predetermined temperature, the bias current I _bIAS fixedly to the threshold current I _th level or immediately before the vicinity level of the semiconductor laser 1 at a predetermined temperature that is controlled by the laser temperature control means 10 A fixed bias current source 11 to be set, and a fixed region _{equal to} or higher than the fixed bias current I _BIAS is fixed as a drive current modulation region. Determine the drive current It is obtained by a regulating means 12.

In such a device invention, the power control means 4 of the first device invention detects a full-power drive current value corresponding to the full power of the semiconductor laser 1. Power does not mean the maximum rated light output of the semiconductor laser 1,
The maximum light output used in the target image recording apparatus.

Further, as the power control means 7 and the bias current variable means 8 of the second device invention, the power level of the semiconductor laser 1 required for determining the bias current _IBIAS may be arbitrarily selected. In this case, from the viewpoint of simplification of the device configuration, the drive current corresponding to the full power of the semiconductor laser 1 may be detected, and the bias current _IBIAS may be determined based on the detected drive current. In consideration of the reduction of the time for determining the current _IBIAS and the life of the semiconductor laser 1, it is possible to detect the drive current corresponding to the low power of the semiconductor laser 1 and determine the bias current _IBIAS based on this. preferable.

Further, in each of the device inventions described above, the drive current modulation region
For 6, 9 and 12, the drive current may be determined as it is from the number of gradation bits of the multi-gradation image data DT, or from the viewpoint of simplification of the configuration, the multi-gradation image data DT It is preferable to reduce the number of gradation bits of the DT to at least the number of bits necessary for gradation reproduction, and determine the drive current from the number of bits.

Further, when designing the drive current modulating means 6, 9, 12, if the function means converts the multi-gradation image data DT into a current value of a predetermined level, it can be modulated continuously or stepwise. Although the modulation can be performed or the design can be changed as appropriate, it is not necessary to continuously modulate the driving current in consideration of the image reproduction accuracy. Rather, the driving current is modulated stepwise from the viewpoint of simplifying the device configuration. The system is preferred.

As a specific mode when adopting such a method,
It has a drive current source composed of a plurality of current sources, and the design can be changed as appropriate, such as determining a desired drive current by appropriately combining these current sources.

In this case, each current source of the drive current source may be of the same capacity or may be appropriately weighted, but from the viewpoint that the modulation level of the drive current can be arbitrarily adjusted. In this case, it is preferable to use one appropriately weighted.

Further, in a type using a drive current source composed of appropriately weighted current sources, from the viewpoint of finely adjusting the value of the drive current corresponding to the multi-tone image data DT, the weighting coefficient of each current source is variably set. It is preferable to design it as follows. Furthermore, if the weighting coefficient of each current source is designed to be variably set, the weighting coefficient is appropriately selected and the image reproducibility of the developing means is corrected to a linear one, thereby improving the image reproducibility. It is possible to keep better.

Although the present invention is directed to a device that reproduces a halftone image by modulating the amount of light of the semiconductor laser 1, it is designed to reproduce a halftone image by appropriately combining with pulse width modulation. No problem.

[Action]

In the process invention, as shown in FIG. 1 (a), in step, driving current modulation area in a state where temperature variations in threshold current I _th of the semiconductor laser 1 is corrected is determined, at step, A drive current based on the multi-gradation image data DT is generated within the determined drive current modulation area.

At this time, since the driving current modulation area is set to follow the threshold current I _th position of the semiconductor laser 1, by a drive current based on multi-gradation image data DT so as to modulate appropriately the drive current modulation region For example, the power level of the semiconductor laser 1 by the drive current based on the multi-gradation image data DT is maintained substantially constant.

In addition, in the device invention as shown in FIG. 1B, the power control means 4 detects a full power drive current value corresponding to the full power of the semiconductor laser 1, while the fixed bias current source 5 The fixed bias current _IBIAS is supplied, and the drive current modulation means 6 sets a drive current modulation area between the full power drive current value and the fixed bias current _IBIAS, and performs multiple gradations in this drive current modulation area. The drive current based on the image data DT is determined.

Further, in the device invention as shown in FIG. 1 (c), the power control means 7 detects a drive current value corresponding to a predetermined power of the semiconductor laser 1, and the bias current variable means 8 detects this drive. Bias current I based on current value
_BIAS is determined, and the drive current modulation means 9 sets a fixed area from the determined bias current _IBIAS as a drive current modulation area, and determines a drive current based on the multi-tone image data DT in the drive current modulation area.

Therefore, in the apparatus invention as shown in FIG. 1 (b) (c), as shown in FIG. 2, the threshold current I _th of the semiconductor laser 1 is displaced with temperature fluctuations, a semiconductor laser 1
Is changed as shown by the imaginary line in FIG. 2, the drive current modulation area A is equal to the threshold current of the semiconductor laser.
Since it is set as A ₁ or A ₂ following the variation δ of I _th , the predetermined multi-tone image data DT (k)
The driving current I _k of the would be set increases by [Delta] I _k corresponding to the variation [delta], the power P _k of the semiconductor laser 1 with respect to multi-gradation image data DT (k) is maintained substantially constant .

Further, in the device invention as shown in FIG. 1 (d), the laser temperature control means 10 controls the temperature of the semiconductor laser 1 to a predetermined level, while the fixed bias current source
_{Reference numeral} 11 sets a fixed bias current _IBIAS , and the drive current modulation means 12 determines a drive current based on the multi-gradation image data DT in the drive current modulation area A in a fixed area from the fixed bias current _IBIAS .

At this time, as shown in FIG.
The temperature T for kept substantially constant, is kept to the threshold current I _th fluctuation width δ is very small, the characteristics of the semiconductor laser 1 is determined substantially uniquely. Therefore, the driving current modulation zone A becomes to be fixed to a certain area, amount that the drive current I _k for the multi-tone image data DT (k) is substantially constant, the power P _k of the semiconductor laser 1 is substantially constant Is kept.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

◎ Example 1 Table of contents I. Overall configuration of image output unit II. Basic configuration of semiconductor laser III. Laser drive circuit (1) Basic configuration (2) APC circuit (3) Modulation circuit IV. Device operation (1) APC operation Process (2) Image formation process I. Overall configuration of image output unit In this embodiment, 256 density gradations (including zero density level)
The present invention is applied to a laser printer that reproduces the input image data as a recorded image.

FIG. 4 shows a laser scanning unit (hereinafter referred to as ROS [Raster Output Scanner]) used in this embodiment.
Is shown.

In the figure, reference numeral 20 denotes a semiconductor laser, 21 denotes a polygon mirror that guides the beam Bm over a predetermined scanning range 1 by reflecting a beam Bm from the semiconductor laser 20 on a reflecting surface 21a that is rotating, and 22 denotes a polygon mirror. A polygon motor for rotating and driving the pogon mirror 21; 23, an fθ lens for correcting the beam Bm from the polygon mirror 21 so as to guide the beam Bm onto the drum-shaped photoconductor 24 at uniform pixel intervals; 25, incidence on the photoconductor 24 Position detection sensor (hereinafter referred to as SOS sensor [Start Of Scan Sensor]) for detecting the scanning start point of beam Bm, 26
Is a mirror interposed in the beam path corresponding to the scanning start point of the photoconductor 24 and guiding the beam Bm to the SOS sensor 25.

Around the photoreceptor 24, a charger 27 for pre-charging the photoreceptor 24, a developing unit 28 for visualizing a latent image on the photoreceptor 24 with toner, and a toner on the photoreceptor 24 Various components of an electrophotographic process, such as a transfer unit 29, on which an image is transferred to a recording sheet (not shown), are provided.In this embodiment, the developing unit 28 uses an exposed portion on the photoconductor 24 as an image portion. Reverse development is performed.

II. Basic Configuration of Semiconductor Laser FIG. 5 shows details of the semiconductor laser 20 used in this embodiment.

In the figure, a semiconductor laser 20 has a stem 31 to which a heat sink 32 is attached. A laser diode chip (hereinafter, referred to as a laser chip) LD is provided on a part of the heat sink 32, and the stem 31 has a laser. A monitor diode chip (hereinafter referred to as a monitor chip) MD for receiving a beam from the chip LD is provided.
The top 31 is covered with a cap 33 having a through-hole 34 for beam irradiation on the top, and the through-hole 34 is closed with a transparent glass 35.

In FIG. 5, reference numerals 36 and 37 denote anode terminals of the laser chip LD and the monitor chip MD, and reference numeral 38 denotes a cathode common terminal of both.

III. Laser Drive Circuit (1) Basic Configuration FIG. 6 is a block diagram showing a laser drive circuit for modulating the light quantity of the semiconductor laser 20.

In the figure, reference numeral 40 denotes an 8-bit image data DT transferred from an image processing unit (not shown).
Latch circuit that takes in in synchronization with VCK, 41 is a latch circuit 40
A gate circuit that passes and blocks image data DT from
The SOS drive signal SOSLDON is used as an opening / closing timing signal of the gate circuit 41. This SOS drive signal SOSLDON
Is the laser chip L when the scanning start point is detected by the SOS sensor 25.
The SOS drive signal SOSLDON is input to the gate circuit 41 when the SOS drive signal SOSLDON is at a low level, in other words, at a timing other than when the scanning start point is detected. When the KATE circuit 41 passes the image data DT and the SOS drive signal SOSLDON is at a high level, the image data DT is unconditionally set to a high level to turn on the laser chip LD at full power. Reference numeral 43 denotes a DA converter for converting the image data DT from the gate circuit 41 into analog data, and reference numeral 45 denotes an amplifier for adjusting the gain of the image data from the DA converter 43.

Reference numeral 50 denotes a bias current I of the laser chip LD.
A bias current source for fixedly setting _BIAS , a modulation circuit 60 for changing the modulation current I _MOD of the laser chip LD according to the gradation level of the image data DT, and a drive current I Is I = I _BIAS + I _MOD .

Further, reference numeral 70 denotes an auto power control circuit (hereinafter referred to as APC) for adjusting the modulation current I _MOD so as to obtain a full power drive current value when the semiconductor laser 20 is at full power (when the laser chip LD emits light at full power). Circuit).

(2) APC circuit The APC circuit 70 is a monitor chip MD of the semiconductor laser 20.
The circuit is closed for a certain period of time when the SOS drive signal SOSLDON is at a high level, and the circuit is opened except during the APC operation. A track and hold circuit 72 for holding the immediately preceding input data value, an amplifier 73 for adjusting the gain of the output from the IV converter 71, and a modulation current _IMOD based on the output from the amplifier 73, A voltage control current source 74 that adjusts the current so that the modulation current level when the laser chip LD emits light at full power.

(3) Basic principle of the modulation circuit the modulation circuit 60, for example as shown in FIG. 7, a differential current switch consisting of the emitter common two transistor Q _A Q _B, the emitter of the transistors Q _A Q _B This is connected to the voltage control current source 74 with a modulation current adjustment resistor R _A R _B interposed therebetween. By raising and lowering the reference voltage V ₀ (corresponding to the gray scale level of the image data DT) base voltage V ₀ + Vi of the transistor Q _A,
The modulation current I _MOD is modulated.

More specifically, for the sake of simplicity, the characteristics of the transistors Q _A Q _B are exactly the same, and the resistance R _A = R
Suppose _B = R, when determining the relationship between the displacement voltage V _i from the reference voltage V ₀ which base voltage of the Q _A and the modulation current I _MOD, as follows in equation (2).

I _MOD = (a / 2R) V _i + (a / 2) I _c − (a / 2R) h · 1n ｛(aI _c -I _MOD )
/ I _MOD ｝ (2) where a: Q _A Q _B grounded base current amplification factor a ≒ 1 h = kT / qk: Boltzmann constant 1.38 × 10 ^-23 [J / K] T: Absolute temperature q: Electron 1.60 × 10 ^-19 [C] h ≒ 26 [mV] at room temperature I _c : current value of voltage-controlled current source In the above equation (2), the third term on the right side, ｛(aI _c -I _MOD ) / I _MOD} is the ratio of the collector current of the transistor Q _a Q _B, Vi in a sufficiently small region (S region in Fig. 8) the value to become close to 1, the above third term can be ignored .

Therefore, in this region, I _MOD = (a / 2R) V _i + (a / 2) I _c (2 ′), and the modulation current I _MOD is calculated using V _i as a parameter, as shown in FIG. It is modulated linearly.

IV. Operation of Apparatus (1) APC Operation Process When detecting the scanning start point by the SOS sensor 25, as shown in FIG. 11, the laser chip LD of the semiconductor laser 20 is determined by the SOS drive signal SOSLDON. The light is turned on only for the time t _APC , and during this time, the APC circuit 70 _operates to adjust the value of the maximum value I _MMAX of the modulation current I _MOD .

At this time, the temperature of the semiconductor laser 20 is assumed to be T _1, the characteristics of the semiconductor laser 20 is as shown in FIG. 9 in T _1, the APC circuit 70, the full power of the laser chip LD P controlling the current value I _c of the voltage controlled current source 74 so that the maximum modulation current I _MMAX (1) is generated that corresponds to the _MAX.
Assuming that the temperature of the semiconductor laser 20 has reached T ₂ , the characteristics of the semiconductor laser 20 are as shown in FIG. 9 T ₂ , but the APC circuit 70 has the full power P _{MAX of the} laser chip LD. maximum modulation current I _MMAX corresponding (2) controlling the current value I _c of the voltage controlled current source 74 to be generated.

Therefore, a semiconductor when the temperature of the laser 20 is T _1, the drive current modulation region of the semiconductor laser 20 is I _BIAS ~I _BIAS + I _MMAX
(1), and also when the temperature of the semiconductor laser 20 is T ₂ are, drive current modulation region of the semiconductor laser 20 is I _BIAS ~I
_BIAS + _IMMAS (2)

(2) Image Forming Process During the APC operation, when the laser chip LD is turned on, the beam Bm from the semiconductor laser 20 emits the SOS sensor 25.
Is incident on. Then, as shown in FIG.
At the stage where the scanning start signal SOS from the sensor 25 is generated and the counter (not shown) has counted the video cook VCK by the predetermined number of pulses _Xn from the rise of the scanning start signal SOS, the laser drive circuit performs the writing operation of the semiconductor laser 20. To start. In the APC operation process at this time, as shown in FIG. 10, it is assumed that the temperature of the semiconductor laser 20 is T, and the maximum modulation current is set to I _MMAX in the APC operation.

At this time, the image data DT (j) having a predetermined number of gradations is
When fed to the modulator circuit 60 via 45, as shown in FIG. 10, the base voltage V ₀ + V _i of the transistor Q _A of the differential current switch of the modulation circuit 60 of the image data DT The modulation current I _MOD (j) is determined based on the above-described equation (2 ′). For this reason, the laser chip LD has I _BIAS + I _MOD
The drive current I (j) of (j) is supplied.

More specifically, as shown in FIG. 4, it is assumed that the semiconductor laser 20 starts an image writing operation after the surface potential of the photoconductor 24 is previously charged by the charger 27.

Now, the driving current I of each pixel PX _i , PX _{i + 1} , PX _{i + 2} , PX _{i + 3} is I
_BIAS , I _BIAS + I _MOD (j1), I _BIAS + I _MOD (j2), I _BIAS + I _MOD (j
3) [However, if I _MOD (j1) <I _MOD (j2) <I _MOD (j3) = I _MMAX ], the optical output P of each semiconductor laser becomes
P _i , P _{i + 1} , P _{i + 2} , P _{i + 3} where P _i = 0 <P _{i + 1} <P _{i + 2} <P _{i + 3} =
P _MAX ], and on the photoreceptor 24 corresponding to each pixel PX _i , PX _{i + 1} , PX _{i + 2} , PX _{i + 3} , a background latent image H having a potential distribution as shown in FIG. And the image portion latent image Z (specifically, Z _{i + 1} , Z _{i + 2} ,
Z _{i + 3} ) are formed.

Thereafter, the developing unit 28 is set to a predetermined developing bias V _B
When operated (reversal development) under the applied condition, the development bias
Development based on the potential difference ΔV (specifically, ΔV _{i + 1} , ΔV _{i + 2} , ΔV _{i + 3} ) between V _B and each image portion latent image Z _{i + 1} , Z _{i + 2} , Z _{i + 3} The degree changes stepwise, and an amount of toner corresponding to each potential difference ΔV is transferred to the photoconductor 24 side. Then, a toner image TZ (specifically, TZ _{i + 1} , TZ _{i + 2} , TZ _{i + 3} ) having a density corresponding to the potential difference ΔV is formed in an area corresponding to each pixel of the photoconductor 24. You.

Thereafter, the toner image TZ on the photoreceptor 24 is transferred to a recording sheet (not shown) by the transfer unit 29, and is fixed to the recording sheet by a fixing unit (not shown).

Embodiment 2 In this embodiment, as in Embodiment 1, the present invention is applied to a laser printer that reproduces input image data of 256 density gradations (including a zero density level) as a recorded image. Although the configuration and the configuration of the semiconductor laser 20 are the same as those of the first embodiment, the configuration of the laser drive circuit is different from that of the first embodiment.

Hereinafter, details of the apparatus will be described focusing on the laser drive circuit according to the table of contents.

Table of contents I. Overall configuration of laser drive circuit II. APC circuit (1) Basic configuration (2) Initial adjustment III. Modulation circuit (1) Switch circuit (2) Drive current source (3) Current synthesis circuit IV. 1) APC operation process (2) Image formation process V. Light intensity modulation experiment example (1) Experimental device (2) Experimental result I. Overall configuration of laser drive circuit FIG. 13 shows a laser drive circuit according to this embodiment.

In the figure, reference numerals 81 and 82 denote gain adjustment variable resistors and an amplifier for adjusting the gain of the output from the monitor chip MD of the semiconductor laser 20, and 90 denotes a mode control signal (Mode Cont.) And an offset on / off signal (Offset) described later.
APC that operates based on ON / OFF) and variably sets the bias current _IBIAS based on the output from the monitor chip MD.
A circuit 100 is a drive current modulation circuit that modulates a drive current according to the density level of the image data DT, and includes a switch circuit.
And a drive current source 130, and determines a modulation current I _MOD according to the density level of the image data DT.
0, the modulation current I _MOD from the modulation current generation circuit 110 and
A current combining circuit 140 for combining the bias current _IBIAS from the APC circuit 90.

In this embodiment, the switch circuit 120 has three switch 121 (to specifically not 121 _a 121 _c),
Depending on the density gradation number of the image data DT is obtained so as to properly off the switch 121 _a to 121 _c.
In this embodiment, in consideration of the fact that the number of reproduced density gradations of a recorded image is generally about 8 density gradations (including a zero density level) as a characteristic of a laser printer, After the DT is converted into 3-bit data by the decoder 111, it is input to the switch circuit 120. On the other hand, the switch circuit 120 turns on all the switches 121 in the SOS lighting period (when the SOS drive signal SOSLDON is at a high level).

Further, the drive current source 130, the plurality of current source 131 (specifically, which is connected in series with the switches 121 _a to 121 _c of the switch circuit 120 and a 131 _a to 131 _c. The embodiment In the above, each of the current sources 131 has a number of unit current sources whose unit reference current I ₀ is adjusted by a power adjustment resistor (Power Adj.) 132, and an arbitrary number of these unit current sources are connected in parallel. and performs weighting by connecting. in this embodiment, to the current source 131 _a no 13
1 _c is adapted to generate a respective _{I 0, 2I 0, 4I 0} .

II. APC Circuit (1) Basic Configuration FIG. 14 is a block diagram showing a basic configuration of the APC circuit 90.

In the figure, reference numeral 91 is a comparator which outputs the results by comparing the magnitude of the output voltage with the comparison reference voltage V _c from the amplifier 82, in this embodiment, when the laser chip LD is full power, amplifier 82 output is adjusted volume of the variable resistor 81 so that the V _c of. A counter 92 operates in response to a mode control signal (Mode Cont.) For selecting a count mode indicating that an APC operation is being performed and a hold mode indicating that a non-APC operation is being performed. In this case, the clock from the oscillator 93 is counted up or down according to the comparison result. Further, reference numeral 94
Is a DA converter that converts the count value from the counter 92 into analog data, and 95 is a current source that generates a bias current _IBIAS based on the output from the DA converter 94. Furthermore, reference numerals 96 to 98 constitute an offset current supply stop system used at the time of initial adjustment described later, 96 is an offset current source, 97 is a resistor for determining an offset current value, and 98 is an offset current value. This is a switch for stopping current supply.

(2) Initial adjustment In order to use the above-described APC circuit 90 as a variable bias current source, the following initial adjustment is required (the fifteenth adjustment).
See figure).

First, the modulation current I _{MOD is set} to zero, and the APC circuit 9
The volume of the variable resistor 81 for gain adjustment is adjusted so that the light output becomes, for example, 1 mW (measured by an optical power meter) by operating only 0. At this time, the gain of the amplifier 82 is set to 10 so that the volume of the variable resistor 81 for gain adjustment does not need to be largely moved at the time of full power emission (the target value of the full power in this embodiment: 10 mW). Double it. Also, a predetermined offset current _IOS (the value is determined by the laser used) is added.

Next, when the output current of the APC circuit 90 is fixed (hold mode) and the added offset current I _OS (about 7 mA in this case) is cut off, the laser chip LD of the semiconductor laser 20 is turned off. At this stage, will be slightly smaller bias current I _BIAS than the threshold current I _th is obtained.

In this case, the reason why the method of directly calculating the threshold current I _th was not adopted was that it was difficult to determine how much light output reached the threshold current I _th, and the high-precision light detection capability Is required.

Then, with the bias current I _BIAS fixed, the maximum current I _MMAX is applied this time (all switches 121 are turned on), and the drive current source is set so that the optical output becomes 10 mW (the target value of full power). Adjust the volume of 131 power adjustment resistors.

Finally, the APC circuit 90 is _operated again with the maximum modulation current _IMMAX applied, and the volume of the gain adjustment resistor 81 is adjusted so that the optical output becomes 10 mW.

As described above, the threshold current I _th of the bias current 20, the bias current _{IBIAS corresponding} to the differential slope efficiency η, and the maximum modulation current I _MMAX can be set.

The above two volume adjustments may be performed only once at the first time as long as the same semiconductor laser 20 is used.

III. Modulation Circuit (1) Switch Circuit (1-A) Basic Principle In this embodiment, the basic principle of each switch 121 of the switch circuit 120 is, for example, as shown in FIG. a differential current switch consisting of _a Q _B, is obtained by connecting the emitter terminals of the transistors Q _a Q _B to the corresponding current source 131 of the driving current source 130. Then, by raising or lowering the base voltage V ₀ + V _i of the transistor Q _A than the reference voltage V _0, it is adapted to turn on and off the switch 121.

More specifically, for simplicity, the transistor
Assuming that the characteristics of Q _A Q _B are exactly the same,
Relationship between the base voltage V _i and the switching current I _s of Q _A is represented by the following equation (3).

_{I s = [(a / {} 1 + exp (-V i / h)}] I D ... (3) where, a: Q _A Q _B grounded base current amplification factor h = kT / qk: Boltzmann constant T: absolute temperature q: Electron charge I _D : Current value of the corresponding current source of the driving current source.

FIG. 17 is a graph showing the relationship between the base voltage V _i of Q _A satisfying the above expression (3) and the modulation current I _s.

Thus, by swinging slightly above or below the base of the transistor Q _A to the reference voltage V _0, it become possible to perform the switching operation.

Note that in this embodiment, a situation that are doing the side driving of the transistor Q _A, when the base drive at each opposite phase of the two transistors Q _A Q _B, the switching current is disturbed occurs a skew This is to avoid.

(1-B) Basic Configuration FIG. 18 is a circuit diagram showing a basic configuration of the switch 121 connected to a predetermined current source 131 of the drive current source 130 in the switch circuit 120.

In the figure, Q _A Q _B serves transistors constituting the differential current switch, resistor for R _A R _B is to adjust the base voltage level to the transistor Q _A, Q _C is a so-called emitter follower, transistor Q _B transistor functioning as a voltage source for the base voltage applied to, R _C is the transistor Q resistor for passing an emitter current of _C, D _a through D _F multistage diode for generating a reference voltage, R _D is the diode
D _A through resistor for supplying a current to D _F, C _A transistor
Capacitor to reduce fluctuation of Q _C base voltage,
Q _D transistors of the current combining circuit acting as a load of the transistor Q _A (described later), R _E is the load resistance of the transistor Q _B.

(1-C) Improved Configuration FIG. 19 shows a further improved configuration of the switch 121 so as to prevent switching distortion and fluctuation of the reference voltage. Note that components similar to those in FIG. 18 are denoted by the same reference numerals as in FIG. 18, and detailed description thereof will be omitted.

 The main improvements in the figure are as follows.

Transistor Q _E, additional this resistor R _H, and substantially equal to the impedance seen from the base of the transistor Q _A Q _B, the rise of the transistor Q _A Q _B, aligning the characteristics of falling, reduced switching distortion Things.

Transistor Q _F of the additional transistor Q _A Q _B load conditions the same west aligns rise, the characteristics of falling, is intended to reduce the switching distortion.

Without base potential to zero when the additional transistor Q _A transistor Q _G diode D _G is turned off, thereby improving the switching speed.

Amount of additional capacitor C _B of the capacitor C _B is intended to be determined experimentally so that the driving waveforms of the transistor Q _A is clean square wave so as to reduce the switching distortion.

It is intended to stabilize the emitter potential of the additional transistor Q _C of the capacitor C _C C _D.

Reference numeral R _F R _G is the resistance for adjusting the base voltage level to the transistor Q _E, R ₁ is the resistance for the flow of the emitter current of the transistor Q _G, C _E will stabilize the emitter potential of the transistor Q _G This is a capacitor for realizing.

(2) Drive Current Source (2-A) Basic Configuration FIG. 20 is a circuit diagram showing a basic configuration of the drive current source 130, which employs a so-called current mirror system.

In the figure, Q _A and R _P are transistors and variable resistors (working as the above-described power adjustment resistors) for determining the current I ₁ , and Q _B is the base of transistors Q _C , Q _D , Q _E , Q _F. transistor for supplying a _{current, R EC, R ED, R} EE, R EF ... is the transistor _{Q C, Q D, Q E} , in order to reduce errors due to variations of Q _F ... base-emitter voltage V _bE of Resistance.

In this embodiment, each of the transistors
_{Q C, Q D, Q E} , ( in this example I ₀₎ Q _F ... collector voltage I _{1 of, I 2, I 3, I} 4 ... are all the same is, to no power 131 _a in FIG. 14
131 _c is, one each unit current source of the current I _0, 2 pieces, has become that by weighting with the four and parallel.

(2-B) Improved Configuration FIG. 21 shows that the switching circuit 120 eliminates adverse effects on the driving current source 130 and reduces switching distortion.
The drive current source 120 is further improved.

 The main improvements in the figure are as follows.

Additional resistor R _A This shed sufficient emitter current in the transistor Q _B, it is intended to reduce the transistor _{Q A, Q C, Q D} , the stabilization of Q _E ... base potential of.

Addition of capacitors C _A , C _B , C _C ... This also stabilizes the base potential of transistors Q _A , Q _C , Q _D , Q _E.

(3) Current Synthesizing Circuit (3-A) Basic Configuration FIG. 22 shows a current synthesizing circuit for synthesizing the modulation current I _MOD and the bias current _IBIAS .

This current synthesizing circuit 140 includes a transistor Q having a common base.
_A be one that combines the modulation current I _MOD and the bias current I _BIAS in (Figure 18, corresponds to Q _D of Fig. 19), lowering the impedance of the line to the switching current is received by the base ground merges Thereby, the mutual interference between the switching transistors of the switch circuit 120 is reduced, and the current distortion of the semiconductor laser 20 is suppressed. still,
Reference sign _VA is a power supply for base voltage.

(3-B) Improved Configuration FIG. 23 shows a further improvement of the current combining circuit of FIG.

 The main improvements in the figure are as follows.

Power up of the transistor Q _A This is an enhancement of the driving capability is obtained by so as to reduce distortion due to the inductance component of the load.

Changing the method of synthesizing the bias current I _BIAS, additional coils L _A which, AC component of the driving current of the laser chip LD (I _MOD)
By separating the DC component (I _BIAS ) from the switching circuit 120, mutual interference between the switch circuit 120 and the APC circuit 90 is suppressed, and switching distortion is reduced.

Additional transistor Q _B This as power supply current I _P is always substantially constant, is obtained so as to reduce the switching distortion.
Incidentally, R _A is the load resistance of the transistor Q _B.

The transistor Q _B is equivalent to a Q _F of Figure 19, and contributes to an improvement of the circuit in both of the switch circuit 120 and a current combining circuit 140.

IV. Device operation (1) APC operation process First, in the SOS lighting section, when the laser chip LD of the semiconductor laser 20 is turned on at full power, the APC circuit 90 finely adjusts the bias current _IBIAS, and in the modulation section, Fix the finely adjusted bias current I _BIAS .

Now, as shown in FIG. 24, when the characteristics of the semiconductor laser 20 is T _a is the bias current is the threshold current I _th
It is variably set to slightly smaller I _BIAS (a), and
Temperature rises, if the characteristics of the semiconductor laser 20 is T _b is the bias current is slightly smaller than the threshold current I _th I
_BIAS (b) is variably set.

At this time, among the respective characteristics, the threshold current I _th
And the bias current I _BIAS is kept constant, and
The maximum modulation currents I _MMAX corresponding to the full power P _MAX of the semiconductor laser 20 are all set to the same magnitude.

(2) Image forming process Now, image data DT (i) having a predetermined number of gradations generates a modulation current.
When input to the switch circuit 120 of 110, the corresponding switch 121 is selectively turned on, and the modulation current generation circuit 110 generates a predetermined modulation current _IMOD .

At this time, as shown in FIG.
If the characteristics of a T _a is the modulation current is I _MOD (a), also, although in the case the characteristics of the semiconductor laser 20 is T _b is the modulation current is I _MOD (b) , Each modulation current I
_MOD (a) and I _MOD (b) have the same size,
As a result, even if the characteristics of the semiconductor laser 20 fluctuate due to the temperature, the bias current _IBIAS fluctuates following the characteristic fluctuation, so that the image data DT (i)
Will also relatively move following the characteristic fluctuation of the semiconductor laser 20. Therefore, it is the power P _i of the semiconductor laser 20 corresponding to the image data DT (i) is kept constant.

Next, the power level of the semiconductor laser 20 according to this embodiment will be described with reference to FIG.

In the figure, DT (1) to DT (7) are 3-bit image data [001] [010] [011] [100] [101] [11]
0] [111]. Each of the image data DT (1) to DT (7) divides the modulation area (I _{BIAS to IBIAS} + I _MMAX ) set in the APC operation process into seven equal parts, thereby respectively corresponding modulation current I _MOD (1) to modulation current I _MOD (7). For this reason, the driving current I corresponding to each of the image data DT (1) to DT (7) includes the bias current I _MOD (1) to the modulation current I _MOD (1) to I _MOD (7).
_BIAS is added.

In this case, the power P ₁ to P ₇ of the semiconductor laser 20 corresponding to the drive current I is set to that the full power output of the semiconductor laser 20 nearly 7 equal parts.

Note that the modulation current I _MOD of the image data [000] is zero, the drive current I at this time is set to _IBIAS, and the power of the semiconductor laser 20 at that time is almost zero.

Thus, the light amount of the semiconductor laser 20 is
When modulated according to the number of gradations of DT, similar to the first embodiment,
A latent image having a potential distribution corresponding to the density of each image data DT is formed on the photoconductor 24, and each latent image is visualized by a developing device 28, and a toner image on the photoconductor 24 is shown. The halftone image is transferred to an external recording sheet and recorded and reproduced.

In particular, in the recording operation process described above, the tone reproducibility of the image is better maintained than in the first embodiment.

That is, in the recording operation process of the type of the first embodiment, the magnitude of the maximum modulation current I _MMAX changes with the temperature fluctuation of the semiconductor laser 20, so that the size of the drive current modulation area itself changes. . At this time, the division of the drive current modulation area into 255 steps remains unchanged. Therefore, if the temperature of the semiconductor laser 20 fluctuates, not only does the amount of current (light amount) per bit differ, but also invalid bits (light Naturally, the number of portions where no output is output is also different, and the light amount modulation accuracy may be slightly roughened accordingly.

However, according to this embodiment, the relative position function of the drive current modulation region with respect to the characteristics of the semiconductor laser 20 can be always kept constant, and the size of the drive current modulation region can be kept constant. The amount of current per bit can be kept constant, and the number of invalid bits can be kept constant. Therefore, the light quantity modulation accuracy can be improved as compared with the first embodiment.

V. Light intensity modulation experiment example (1) Experimental device FIG. 26 shows a light intensity measurement device for measuring the light intensity modulation state of the device according to the above embodiment.

In the figure, reference numeral 150 denotes a light receiving element composed of a high-speed pin photodiode for simply observing an optical output waveform, V _m
Is the voltage applied to the light receiving element 150 (+15 in this embodiment)
(V)), R _m is a resistance (1 KΩ in this embodiment) for applying a reverse bias voltage to the light receiving element 150, and C _m and C _n are light receiving elements
A capacitor for stabilizing the reverse bias voltage of 150, _RL is a resistor (560 Ω in this embodiment) for converting the light output current of the light receiving element 150 into a voltage and extracting it, and 151 is a digitizing oscilloscope [Digitizing Osilloscope]
(In this example, HP1653 manufactured by Hewlett-Packard Company was used.
0A) and 152 are probes for taking the optical output into the digitizing oscilloscope 151.

In this measurement device, the resistance _RL and the probe input capacitance
A pole is formed by C _IN and the waveform becomes dull. Therefore,
When importance is placed on the transient characteristics, it is necessary to set _RL small, and when importance is placed on the S / N ratio of the measurement, it is necessary to set _RL large.

In this measuring device, the reason why R _L = 560Ω is that the S / N ratio is emphasized, and it is considered that the actual light output rises and the falling edge becomes sharper than the observed waveform.

It is preferable to use an optical oscilloscope or the like for accurate measurement of the optical waveform.

(2) Experimental result An experiment of light quantity modulation performed using the above-described light quantity measuring device,
APC (10μ)
s) → light off (50μs) → modulation (100μs) → light off (50μs)
s) was repeated. Also, the modulation part is, for example, (000) → (001) → (010) → (011) →
Modulation was performed by repeating eight data such as (100) → (101) → (110) → (111) as one set.

The length of one piece of data is 50 ns. The left side of the 3-bit input data is the upper bit (MSB) and the right side is the lower bit (LSB).

FIGS. 27 (a) and 27 (b) show current waveforms when a resistive load is connected instead of a laser. Figure 27 (a) shows that the input data is (000) → (001) → (010) → (011) → (100) →
When (101) → (110) → (111), FIG. 27 (b) shows (0
10) → (011) → (100) → (101) → (110) → (101)
→ (100) → (011) respectively. 27 (a) and 27 (b) indicate one data area, and the numbers in parentheses in the figure indicate the input data, respectively (the same applies to the subsequent figures in FIG. 27). ).

Now, the optical output waveform when the current waveform is as shown in FIG.
27 (c) to (f).

FIG. 27 (c) shows the beginning of the modulation section, and FIG. 27 (d) shows the end of the modulation section. According to the figure, it is understood that there is almost no change in the waveform, and there is almost no influence of the temperature change during this period. FIGS. 27 (e) and 27 (f) show the same parts as those in FIGS. 27 (c) and 27 (d) in the accumulation rate mode of the digitizing oscilloscope 151. . Even in this mode, it is understood that the light output changes stepwise according to the input data, and it is understood that the light quantity is modulated with 3-bit accuracy.

27 (g) and (h) show optical output waveforms when the current waveform is as shown in FIG. 27 (b).

FIG. 27 (g) shows the beginning of the modulation section, and FIG. 27 (h) shows the end of the modulation section. According to the figure, although a slight hysteresis phenomenon (a phenomenon in which the current value for the same data differs when the current increases and decreases) is seen,
It is understood that the light output changes stepwise according to the input data, and it is understood that the light amount is modulated with 3-bit accuracy.

In addition, FIGS. 27 (i) and (j) show the light output waveforms in the case of repeating all light emission and extinguishing for each dot.

FIG. 27 (i) shows the beginning of the modulation section, and FIG. 27 (j) shows the end of the modulation section. According to the figure, it is understood that ON / OFF for each dot is surely performed, and no change in the waveform is observed between the beginning and the end of the modulation section. It is to be noted that the gradual fall in the figure seems to be a problem of the measuring device as described above.

27 (k) and (l) show the light output waveforms when the light is continuously lit in all the light emission during the modulation period.

FIG. 27 (K) shows the beginning of the modulation section, and FIG. 27 (l) shows the end of the modulation section. According to the figure, it is understood that there is almost no change in the optical output between the beginning and the end of the modulation section, and droop during this period does not matter.

In this embodiment, heat radiation of the semiconductor laser is not particularly considered.

◎ Third Embodiment Table of Contents I. Overall Configuration of Image Output Unit II. Laser Drive Circuit (1) Basic Configuration (2) Weight Setting of Drive Current Source III. Operation of Device I. Overall Configuration of Image Output Unit The present invention is applied to a so-called one-pass two-color (for example, red and black) laser printer.

In FIG. 28, reference numeral 200 denotes, for example, a positively charged photoreceptor, 201 denotes a charger for pre-charging the photoreceptor 200, 202 denotes a ROS used in this embodiment, and 203 denotes a bias using, for example, a positive red toner. A first developing device of a system, 204 is a second developing device of a bias system using, for example, a black toner of a negative polarity, 205 is a pre-transfer processing charger for aligning the polarity of a toner image on the photoconductor 200, and 206 is a recording sheet 207. A transfer device for transferring the toner image on the photoconductor 200 to the photoconductor 200; a static eliminator 208 for removing the recording sheet 207 electrostatically attached to the photoconductor 200; a cleaner 209 for removing residual toner on the photoconductor 200; Reference numeral 210 denotes an eraser lamp for removing the residual charges on the photoconductor 200, and reference numeral 211 denotes a fixing unit that fixes a toner image on the recording sheet 207 after the transfer process. In this embodiment, the first developing device
It reproduced image characteristics showing the relationship between the 203 and the input image density and recorded image density of the second developing unit 204, FIG. 30 Y _R (first developing device characteristics), as Y _B (second developing device characteristics) , Each one is different.

Details of the ROS 202 used in this embodiment are shown in FIG.

In the figure, 221 is a semiconductor laser for image formation of the first color, 222 semiconductor lasers for image formation of second color, a polygon mirror for reflecting by the beam B _m different angles from the laser 221, 222 of both 223, 224 the polygon motor 225 fθ lens, a mirror 226 is guided to the first exposure section E ₁ to the position of the beam B _m from the laser 221 of the first color before the first developing unit 203 of the photoreceptor 200, 227 two mirror for guiding the beam B _m from the laser 222 of the color in the second exposure section E ₂ is positioned in front of the second developing unit 204 of the photoreceptor 200, 228 and 229 scan start position of the laser beam of the first color and the second color Are SOS sensors that respectively detect.

The drive control system of the ROS 202 is configured as follows.

The In Figure 28, reference numeral 230 is an image processing unit for outputting after converting first color (red) and multi-gradation image data DT _R 256 gradations of the secondary color (black), the DT _B to 3-bit data by the decoder , 231 from the image data DT so-called FIFO, 232 is the image data DT _B the first exposure portion E ₁ from the image processing unit 230 is a memory first in, first out _{scheme R} temporarily storing output from the image processing unit 230 output for gap memory after storing only the scanning time corresponding to the gap GP between the second exposure section E _2, 233 is the amount of light modulation driving according to laser 221 of the first color to the image data so that the exposed portions become image area A first laser drive circuit 234 is a second laser drive circuit that drives the laser 222 of the second color in accordance with image data in such a manner that the non-exposed portion becomes an image portion. The drive of the polygon motor 224 is controlled by a motor drive circuit (not shown).

II. Laser Drive Circuit (1) Basic Structure FIG. 31 is a circuit diagram showing a basic structure of the first and second laser drive circuits 233 and 234.

First and second laser drive circuits 233, 23 according to this embodiment
_{Reference numeral} 4 denotes an APC circuit 90 for variably setting the bias current _IBIAS and driving in accordance with the number of density gradations of the image data DT (8 density gradations including the zero density level), similarly to the second embodiment. And a modulation circuit 100 for modulating current.
In particular, the configuration of the drive current source 130 is different from that of the second embodiment. Note that components similar to those of the second embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof will be omitted.

In this embodiment, the drive current source 130 is connected to seven current sources 131 (specifically, 131 _a to 131 _g ) each having a basic element as shown in FIG. Variable resistors 133 (specifically, 133 _a to 131 _g ), and the currents from the respective current sources 131 are changed to K ₁ I ₀ and K ₂ by appropriately changing the respective resistance values of the variable resistors 133. I ₀ … K
_It can be adjusted to ₇ I ₀ (K _{1 to} K ₇ : weighting coefficient). In particular, in the this embodiment, as described later, the respective weighting factors K ₁ ~K ₇ in consideration of the reproduced image characteristics of the developing devices 203 and 204 are set.

In this embodiment, the switch circuit 120 is composed of seven switches 121 connected to each current source 131, and each switch 121 is selectively turned on according to the image data DT. ing.

(2) Weight setting of drive current source (2-A) First laser drive circuit FIG. 32 (a) is a characteristic diagram showing the relationship between the exposure amount P by the first developing device 203 and the image recording density D (FIG. 30). it is equivalent) in FIG Y _R.

In the figure, to eight steps D ₀ not at equal intervals the image dark recording density D is divided into D _7, to no P ₀ the exposure amount P corresponding to each and P _7. In this case, the exposure amount P ₀ to P ₇ has become what non equal parts.

Then, as shown in FIG.
For one of the characteristics, to not the exposure amount P ₀ to the modulation current I _MOD (0) no corresponding to P ₇ obtains the I _MOD (7), with respect to modulation of the respective currents I _MOD (0) to I _MOD (7) Image data
DT (0) to DT (7) [(000) (001) (010) ... (1
10) (111)]. The modulation current I _MOD corresponding to the image data DT (0) [(000)]
(0) is zero.

At this time, it is necessary to weight each current source 131 of the drive current source 130 so that each of the modulation currents I _MOD (1) to I _MOD (7) is generated.

(2-B) the second laser driving circuit Fig. 33 (a) is a characteristic diagram showing the relationship between the exposure amount P and the image recording density D by the second developing unit 204 (corresponding to FIG. 30 Y _B).

In the figure, to eight steps D ₀ not at equal intervals the image dark recording density D is divided into D _7, to no P ₀ the exposure amount P corresponding to the respective P ₇ (P ₇ is zero) to. In this case, the exposure amount P ₀ to P ₇ has become what non equal parts.

Then, as shown in FIG.
For one of the characteristics, to not the exposure amount P ₀ to the modulation current I _MOD (0) no corresponding to P ₇ obtains the I _MOD (7), with respect to modulation of the respective currents I _MOD (0) to I _MOD (7) Image data
DT (0) to DT (7) [(000) (001) (010) ……
(110) and (111)]. still,
Modulation current I corresponding to image data DT (0) [(000)]
_MOD (0) is I _MMAX .

At this time, it is necessary to weight each current source 131 of the drive current source 130 so that each of the modulation currents I _MOD (0) to I _MOD (6) is generated.

In this embodiment, when performing eight-stage nonlinear current modulation, the first laser drive circuit 233 requires I _MOD
Seven current sources 131 corresponding to (1) to I _MOD (7)
In the second laser drive circuit 234, seven current sources 131 corresponding to I _MOD (0) to I _MOD (6) are prepared and individually weighted, but should be generated. When the modulation current level is obtained by combining a plurality of current sources 131, the combined use of the current sources 131 becomes possible, and the number of current sources 131 can be reduced accordingly.

III. Operation of Device Next, the operation of the image output unit according to this embodiment will be described.

Image data DT _R from the image processing unit 230, DT _B
Is transmitted to the first laser drive circuit 233 and the second laser drive circuit 234 via the FIFO 231 or the gap memory 232.

At this time, first, the first laser drive circuit 233
Drives, latent image Z ₁ exposure portion as shown in FIG. 34 (a) is an image portion is formed in the first exposure portion E ₁ of the photosensitive member 200.
The developing bias V This latent image Z ₁ is at first developing unit 203
Once developed under _B1, as shown in the figure, the first toner image TN ₁ is formed.

Thereafter, the second laser drive circuit 234 drives the laser 222, the latent image Z ₂ of unexposed portion as shown in FIG. 34 (b) to the second exposure portion E ₂ of the photosensitive member 200 is an image portion It is formed. When the latent image Z ₂ is developed under the developing bias V _B2 by the second developing unit 204, as shown in the figure, the first toner image
TN ₂ is formed.

Then, these toner images TN ₁ and TN ₂ are made uniform in polarity by the pre-transfer processing charger 205, then transferred to the recording sheet 207 by the transfer unit 206, and then fixed by the fixing unit 211. .

In such a recording operation process, the light amount modulation control of the semiconductor lasers 221 and 222 is performed so as to correct the image reproduction characteristics of each of the developing devices 203 and 204, and as shown in FIG. It has a linear relationship. Therefore, the two-color image is reproduced in an extremely good state.

Example 4 The basic configuration of the laser drive circuit according to this example is
As shown in FIG. 36, the configuration is substantially the same as that of the second embodiment, _except that the APC circuit 250 that variably sets the bias current _IBIAS is different from that of the second embodiment. The same components as those in the second embodiment are denoted by the same reference numerals as in the second embodiment, and the detailed description thereof will be omitted.

In the figure, the APC circuit 250 includes an IV converter 251 for converting a current from a monitor chip MD of the semiconductor laser 20 into a voltage, and an AD converter for converting an output of the IV converter 251 into a digital value. 252, a processing logic 253 for performing a predetermined operation based on the data from the AD converter 252, and a DA for converting an output from the processing logic 253 into an analog quantity.
It includes a converter 254 and a current source 255 that determines a bias current _IBIAS based on an output from the DA converter 254.

In this embodiment, the processing logic 253 is
As shown in the figure, in each APC operation cycle, the output of the monitor chip MD becomes a predetermined value (in this embodiment, a low power P _i set in advance near the threshold current I _{th in} the linear region of the characteristic of the semiconductor laser 20 _). ) Until the output of the monitor chip MD reaches a predetermined value, and when the output of the monitor chip MD reaches a predetermined value, a constant difference current ΔI (in this embodiment, a predetermined power
The difference signal corresponding to the current I _APC from the current source 255 during the APC operation corresponding to P _i and the current value at a level slightly lower than the threshold current I _th ) is subtracted from the bias current increase signal, This is kept constant and output is continued until the next APC operation cycle.

Therefore, according to this embodiment, during the APC operation process, the APC circuit 250 sets the output of the monitor chip MD to a low power P during the APC section as shown in FIGS. 37 and 38.
_The bias current I _BIAS is sequentially increased until the predetermined value of _i is reached, and when the output of the monitor chip MD reaches the predetermined value, I
_Assuming that _BIAS = I _M , the value obtained by subtracting the difference current ΔI from this I _M , that is, I _M −ΔI is calculated as the bias current I _BIAS
And hold the value as a hold section thereafter.

In this type, basically the same operation and effect as those of the second embodiment are obtained, but since it is not necessary to make the semiconductor laser 20 emit light at full power in the APC operation process, the APC operation time is shorter than that of the second embodiment. In addition to the shortening, the life of the semiconductor laser 20 is extended by the shortening of the lighting time itself of the semiconductor laser 20 during the APC operation.

In this embodiment, the APC circuit 250 is used for a halftone image reproducing laser printer. However, the APC circuit 250 is also used for a binary image reproducing laser printer or the like.
Of course can be applied.

５Embodiment 5 In this embodiment, the present invention is applied to a laser printer. However, unlike the above embodiments, the semiconductor laser 20 is controlled to a constant temperature by a temperature control system 260 as shown in FIG. At the same time, the laser drive circuit 270 controls the drive.

In this embodiment, the temperature control system 260 includes a temperature sensor 26 at the stem or the gap of the semiconductor laser 20.
1 and a cooling element 262 such as a Peltier element, and the output of the temperature sensor 261 is input to a temperature compensation circuit 263, and the temperature compensation circuit 263 controls the cooling element 262 according to the output level of the temperature sensor 261. The semiconductor laser 20 at a constant temperature T
_{This is} to keep it at ₀ .

Further, the laser driving circuit 270, as shown in FIG. 40, a fixed bias current source 271 to set the bias current I _BIAS of the slightly lower level than the threshold current I _th in the constant temperature T _0, Example 2 And a modulation circuit 100 (a modulation current generation circuit 110 including a switch circuit 120 and a drive current source 130 and a current synthesis circuit 140) having the same configuration as the above.

Therefore, according to this embodiment, since the temperature control system 260 keeps the temperature of the semiconductor laser 20 constant, the characteristics of the semiconductor laser 20 are kept almost unchanged, as shown in FIG. Is set to

For this reason, when the image data DT (i) having a predetermined number of gradations is input to the switch circuit 120 of the modulation circuit 100, the modulation current generation circuit 110 outputs the modulation current I corresponding to the image data DT (i). _MOD (i) is generated, and the current synthesizing circuit 140 of the modulation circuit 100 adds the modulation current I _MOD (i) and the bias current _IBIAS, and generates a driving current I corresponding to the image data DT (i).
Becomes to generating, the image data DT (i) drive current I for becomes always constant, the optical output P _i of the semiconductor laser 20 associated therewith is also kept constant at all times.

Therefore, if an appropriate drive current is modulated for the image data DT of each gradation number, the light quantity of the semiconductor laser 20 is accurately modulated according to the density data of each image data DT.

〔The invention's effect〕

As described above, according to the image recording method of the present invention, even if the characteristics of the semiconductor laser fluctuate, the temperature fluctuates by following the characteristics of the semiconductor laser while effectively correcting the temperature fluctuation. A drive current corresponding to the density level of the gradation image data is generated, and the light amount of the semiconductor laser is modulated based on the drive current. The light output can be kept substantially constant, so that the light quantity modulation accuracy of the semiconductor laser can be improved and the multi-gradation recorded image quality can be kept good.

In particular, according to the image recording method of the present invention, since the drive current modulation area of the semiconductor laser is set to be equal to or higher than the bias current set to the level immediately before the threshold current, the image data of which the optical output cannot be obtained is obtained. In addition to minimizing the number of invalid bits, at the set point of the bias current, since the semiconductor laser is in a spontaneous light emission state without oscillating, light from the semiconductor laser is irradiated on the photoconductor and an image is formed. Defects can be reliably avoided.

Further, according to the image recording apparatus of the second aspect, even if the characteristics of the semiconductor laser fluctuate, the drive current modulation range is variably set based on the maximum drive current corresponding to the full power of the semiconductor laser. Therefore, it is possible to effectively suppress the variation in the optical output of the semiconductor laser according to the density level of the desired multi-tone image data, and to improve the light quantity modulation accuracy of the semiconductor laser.

Further, according to the image recording apparatus of the present invention, even if the characteristics of the semiconductor laser fluctuate, the bias current is variably set based on the drive current corresponding to the predetermined power of the semiconductor laser, and the variable bias current is Since the constant area is set as the drive current modulation area, the light output of the semiconductor laser can be stabilized stably in accordance with the density level of the desired multi-tone image data. The light quantity modulation accuracy of the laser can be further improved as compared with the type described in the second aspect.

In particular, according to the image recording apparatus of the present invention, since the bias current is variably set based on the drive current corresponding to the low power of the semiconductor laser, the time for variably setting the bias current is reduced. While being able to
When the bias current is set, the power of the semiconductor laser can be suppressed, and the life of the semiconductor laser can be extended.

Furthermore, according to the image recording apparatus of the present invention, since the temperature change of the semiconductor laser is corrected to minimize the temperature fluctuation of the characteristics of the semiconductor laser, the drive current modulation region is uniquely set. It is possible to easily stabilize the light output of the semiconductor laser according to the density level of the desired multi-tone image data, and to improve the light quantity modulation accuracy of the semiconductor laser.

Further, according to the image recording apparatus of any one of claims 6 to 9, a driving current modulating means includes a driving current source composed of a plurality of current sources, and the driving current is appropriately combined with each other. Was decided.
The configuration of the drive current modulating means can be simplified as compared with a method of continuously modulating the drive current.

According to the image recording apparatus of the sixth aspect, the drive current is determined by the number of the same current sources.
In modulating the integral multiple of the drive current, the configuration can be simplified.

According to the image recording apparatus of any one of claims 7 to 9, the drive current is determined by appropriately combining a plurality of weighted current sources, so that the modulation level of the drive current can be arbitrarily set. In addition to being able to set, if a drive current is generated by combining a plurality of current sources with different weights, it is possible to secure a large number of drive current modulations with a small number of current sources.

In particular, according to the image recording apparatus of the eighth aspect, the weighting coefficient of each current source of the drive current source can be variably set, so that when determining the drive current corresponding to the density level of the image data, The modulation width of the drive current can be finely adjusted. According to the image recording apparatus of the ninth aspect, the image reproduction characteristic of the developing means can be corrected to a linear one, so that the reproduction quality of the halftone image can be kept extremely good.

[Brief description of the drawings]

FIG. 1 (a) is an explanatory view schematically showing an image recording method according to the present invention, FIGS. 1 (b) to 1 (d) are explanatory views each showing a schematic configuration of an image recording apparatus according to the present invention, and FIG. FIG. 3 is an explanatory diagram showing the operation of the image recording apparatus according to FIGS. 1 (b) and (c), FIG. 3 is an explanatory diagram showing the operation of the image recording device according to FIG. 1 (d), and FIG. RO of the image recording apparatus according to Example 1
S is a perspective view showing S, FIG. 5 is a partially cutaway perspective view showing a configuration of a semiconductor laser used in Embodiment 1, and FIG.
FIG. 7 is a block diagram showing a laser driving circuit used in FIG. 7, FIG. 7 is a principle circuit diagram showing a basic configuration of the modulation circuit shown in FIG. 6, and FIG.
FIG. 9 is an explanatory diagram showing the operation of the modulation circuit, FIG. 9 is an explanatory diagram showing an APC operation process of the laser drive circuit, FIG. 10 is an explanatory diagram of an image writing operation process of the laser drive circuit, and FIG.
FIG. 12 is a timing chart showing an entire sequence of S, FIG. 12 is an explanatory diagram showing an image forming process on a photoconductor, FIG. 13 is a block diagram showing a laser drive circuit used in the image recording apparatus according to the second embodiment, 14 is a block diagram showing details of the APC circuit in FIG. 13, FIG. 15 is an explanatory diagram showing an initial setting operation process of the APC circuit, and FIG. 16 is a basic configuration of a switch portion of the modulation circuit according to the second embodiment. FIG. 17 is an explanatory diagram showing the operation thereof, FIG. 18 is a circuit diagram showing details of the switch portion, FIG. 19 is a circuit diagram showing an improvement plan of the switch portion, and FIG. FIG. 21 is a circuit diagram showing details of a current source of the modulation circuit according to the second embodiment, FIG. 21 is a circuit diagram showing an improvement plan of the current source, and FIG. 22 is a detail of a current synthesis portion of the modulation circuit according to the second embodiment. FIG. 23 is a circuit diagram showing an improvement plan of the current synthesizing part, and FIG. 24 is an embodiment. FIG. 25 is an explanatory diagram showing an operation process of the laser drive circuit of FIG. 25, FIG. 25 is an explanatory diagram showing a relationship between a drive current for each image data and a light output of a semiconductor laser, and FIG. Circuit diagram showing a device configuration for easily measuring the laser output,
27 (a) to (1) are graphs showing various results measured using the apparatus according to FIG. 26, FIG. 28 is a block diagram showing the overall configuration of the image recording apparatus according to Embodiment 3, and FIG. FIG. 30 is a perspective view showing details of the ROS used in the third embodiment, FIG. 30 is a graph showing the reproduced image characteristics of the developing device used in the third embodiment, and FIG. 31 is a laser drive circuit used in the third embodiment. 32 (a) and (b) are explanatory diagrams showing the principle of weighting the current source of the first laser drive circuit, and FIGS. 33 (a) and (b) are current diagrams of the second laser drive circuit. 34 (a) and 34 (b) are explanatory diagrams showing an image recording process of the image recording apparatus according to the third embodiment, and FIG. 35 is an input image density and recorded image of the third embodiment. FIG. 36 is a graph showing the relationship with the density. FIG. 36 shows details of a laser drive circuit used in the image recording apparatus according to the fourth embodiment. 37 is an explanatory diagram showing the principle of setting the bias current of the laser drive circuit, FIG. 38 is a timing chart showing the process of setting the bias current, and FIG. 39 is a diagram showing the image recording apparatus according to the fifth embodiment. FIG. 40 is a block diagram showing the main part, FIG. 40 is a block diagram showing the details of the laser drive circuit, FIG. 41 is an explanatory diagram showing the operation process, FIG. 42 is an explanatory diagram showing the characteristics of the semiconductor laser, FIG. FIG. 4 is an explanatory diagram showing a temperature fluctuation state of characteristics of a semiconductor laser. [Explanation of _Signs ] I _th Threshold current of semiconductor laser I _BIAS Bias current 1 Semiconductor laser 2 Photoconductor 3 Developing unit 4,7 Power control unit 5,11 Fixed bias current source 6,9,12 ... Drive current modulation means 8 ... Bias current variable means 10 ... Laser temperature control means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/44 B41J 2/52 H04N 1/23

Claims (9)

(57) [Claims] A light source for modulating a light amount from a semiconductor laser in accordance with a density level of multi-tone image data (DT) of each pixel;
A latent image corresponding to each pixel is formed on the photoconductor (2),
An image recording method for visualizing each latent image by a developing means (3), wherein a temperature of a threshold current (I _th ) of the semiconductor laser (1) is modulated when modulating a light amount of the semiconductor laser (1). A drive current modulation area determining step of correcting the fluctuation and determining a drive current modulation area for an area _{equal to} or greater than a bias current (I _BIAS ) set to a level immediately before the threshold current (I _th ); Image data (DT) within the driving current modulation range
A driving current generating step of generating a driving current of the semiconductor laser (1) according to the density level of the semiconductor laser (1). 2. The method according to claim 1, wherein the amount of light from the semiconductor laser is modulated according to the density level of multi-tone image data of each pixel.
A latent image corresponding to each pixel is formed on the photoconductor (2),
An image recording apparatus for visualizing each latent image by a developing means (3), wherein a full-power drive current value corresponding to the full power of the semiconductor laser (1) is supplied when the semiconductor laser (1) is not scanned. intermittently the power control means (4) for detecting the threshold current (I _th) minimum variation level or bias current immediately before the vicinity level of the semiconductor laser (1) (I
_BIAS ) fixed bias current source (5)
Between the full power drive current value and the fixed bias current (I _BIAS ) as a drive current modulation area, and in this drive current modulation area, drive according to the density level of multi-tone image data (DT). Drive current modulation means for determining current (6)
An image recording device comprising: 3. A light amount from a semiconductor laser (1) is modulated according to a density level of multi-tone image data (DT) of each pixel,
A latent image corresponding to each pixel is formed on the photoconductor (2),
An image recording apparatus for visualizing each latent image by a developing means (3), wherein a driving current value corresponding to a predetermined power of the semiconductor laser (1) is intermittently set during a non-scanning operation of the semiconductor laser (1). And a threshold current (I _th ) of the semiconductor laser (1) based on a predetermined drive current value detected by the power control means (7).
A bias current varying means (8) for changing a bias current (I _BIAS ) set to a level or a level immediately before the level, and a fixed area is determined as a drive current modulation area from the variable bias current (I _BIAS ). An image recording apparatus comprising: a drive current modulation means (9) for determining a drive current according to a density level of multi-tone image data (DT) in a current modulation area. 4. The apparatus according to claim 3, wherein the power control means (7) sets a drive current value of the semiconductor laser (1) at a low power level as a detection current value, and the bias current variable means (8) controls the bias current variable means (8). By subtracting a predetermined value from the detected current value, the bias current (I
_BIAS ) is determined. 5. A light amount from a semiconductor laser (1) is modulated according to a density level of multi-tone image data (DT) of each pixel,
A latent image corresponding to each pixel is formed on the photoconductor (2),
An image recording apparatus for visualizing each latent image by a developing means (3), comprising: a laser temperature control means (10) for controlling a temperature of a semiconductor laser (1) to a predetermined temperature; A fixed bias current source (11) for fixedly setting a bias current (I _BIAS ) at or near a threshold current (I _th ) level of the semiconductor laser at a predetermined temperature controlled by (10); Drive current modulation means for determining a fixed area _{equal to} or higher than the current (I _BIAS ) as a fixed drive current modulation area and determining a drive current corresponding to the density level of multi-tone image data (DT) in the fixed drive current modulation area. (12) An image recording apparatus comprising: 6. The driving current modulating means (6, 9, 12) according to claim 2, wherein said driving current modulating means (6, 9, 12) has a driving current source comprising a plurality of identical current sources. An image recording apparatus wherein a desired drive current is determined by appropriately combining sources. 7. The driving current modulating means (6, 9, 12) according to claim 2, wherein the driving current modulating means (6, 9, 12) has a driving current source comprising a plurality of weighted current sources. An image recording apparatus wherein a desired drive current is determined by appropriately combining current sources. 8. An image recording apparatus according to claim 7, wherein a weighting coefficient of each of said driving current sources is variably set. 9. The driving current source according to claim 7, wherein a weighting coefficient of each current source of the driving current source is set so as to correct the image reproduction characteristic of the developing means to a linear one. An image recording apparatus, comprising: