JP2001334701A - Device for controlling laser power of electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for variably controlling a laser power of a semiconductor laser concerning with an electrophotographic device, for collecting the change of the amount of a toner adhesion in the result of the effects of the temperature and humidity in an electrophotographic printing device which varies with every multistage laser power at the time of the laser power modulation. SOLUTION: A laser power can be variably controlled in contrast to all values of a multistage laser power by variably controlling a voltage set by the laser power by a calculation means of a microprocessor-controlled computer and providing a variably controlling means for the voltage set by the laser power as many as the values of the multistage laser power at the time of the laser power modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to variable control of laser power of an electrophotographic apparatus using a semiconductor laser.

[0002]

2. Description of the Related Art In recent years, in the POD market, higher image quality has been demanded. In addition to simply securing image density above a certain level and reducing fog, it is also necessary to faithfully reproduce halftones, graphics and character characters. Is required.

In the prior art, there is a laser power modulation method as a toner adhesion amount control means for faithfully reproducing halftones, graphics, and character characters. In the laser power modulation method, the laser power is set to a multi-step fixed value, and the laser power is switched according to the print pattern, thereby controlling the toner adhesion amount per dot. The laser power modulation method is based on the relationship between the toner adhesion amount on the photoconductor and the laser power shown in FIG. 3, the dead area 74 where the toner does not adhere even if the laser power 73 increases, and the toner adhesion amount according to the increase in the laser power 73. Of the three regions, an unsaturated region 75 where the 72 increases and a saturated region 76 where the toner adhesion amount 72 does not increase even when the laser power 73 increases, a multi-step laser power value is set in the unsaturated region 75. Then, the amount of toner adhesion is controlled by performing laser power modulation for switching the laser power according to the print pattern.

[0004] In the unsaturated region 75 of the photoreceptor, the relationship between the amount of toner adhering on the photoreceptor and the laser power changes due to the effects of temperature and humidity in the electrophotographic printing apparatus. Generally, when the temperature in the electrophotographic printing apparatus rises, the sensitivity of the photoconductor increases, and the relationship between the amount of toner adhered on the photoconductor and the laser power is indicated by a solid line in FIG. Changes to characteristics. At this time, the unsaturated region 75 changes to the second unsaturated region 77.

Due to laser power modulation, the unsaturated region 75
If the laser power setting value PL'78 and the laser power setting value PH'82 are set in two steps, the toner adhesion amount of the laser power setting value PL'78 becomes the toner adhesion amount initial value TL80 due to a change in the characteristics of the photoconductor. Is the value obtained by adding the toner adhesion amount change value ΔTL81 to the laser power setting value P.
The toner adhesion amount of H'82 is the toner adhesion amount initial value TH84.
And the toner adhesion amount change value ΔTH85 is added to the image density, the image density is increased, and the gradation is deteriorated.

As one means for solving the problem, the laser power setting value PL'78 and the laser power setting value PH'82 at the time of laser power modulation shown in FIG. ΔPL79 is reduced to a laser power set value PL ″ 86, and a laser power variable value ΔPH83 is reduced to a laser power set value PH ″ 87 from the laser power set value PH′82 to reduce the toner adhesion amount for each laser power. Laser power variable control for correction is given. In this case, the laser power set value requires four set values: a laser power set value PL'78, a laser power set value PH'82, a laser power set value PL "86, and a laser power set value PH" 87.

FIG. 2 shows an example of a conventional laser power control system capable of laser power modulation. The number of laser power modulation steps is two.

The laser power control system shown in FIG. 2 will be described. The laser driver PL'38 applies the reference voltage V1ref62, which is the output of the reference voltage source 66, as the laser power setting voltage VrL'46 to the positive phase input of the comparator 64, and the monitor voltage Vm to the negative phase input of the comparator 64.
Apply L'50. The charge / discharge control circuit 65 charges the hold capacitor L'54 when the output of the comparator 64 is at the High potential, and discharges the hold capacitor L'54 when the output of the comparator 64 is at the Low potential. The switching current source 67 includes a hold capacitor L '.
The reference voltage V2ref63, which is the output of the reference voltage source 66, is compared with the hold voltage VchL'58 charged in 54, and the reference voltage V2ref63 is compared with the hold voltage VchL '.
When it is larger than 58, the switching current value is increased, and when the reference voltage V2ref63 is smaller than the hold voltage VchL'58, the switching current value is decreased. The current switching circuit 68 switches the laser diode 17 with a switching current source 67 by a laser drive signal (not shown).
Drive with the current value set in. A monitor current Im20 proportional to the laser power Po19 of the laser diode 17 flows through the photodiode 18. Monitor load resistance R
mL'42 is a value obtained by converting the monitor current Im20 to the monitor voltage Vm.
Convert to L'50. The monitor voltage VmL'50 is fed back to the comparator 64. With the above feedback routine, the laser driver PL'38 can control the laser power of the semiconductor laser 16 to be constant.

The laser driver PH'40 has the same circuit as the laser driver PL'38, and has a monitor load resistance R
The laser power different from that of the laser driver PL'38 can be set by mH'44. The laser power is modulated by switching between the laser driver PL'38 and the laser driver PH'40 according to the printing pattern.

Although the laser power control system shown in FIG. 2 can perform laser power modulation in two stages, the temperature in the electrophotographic printing apparatus in relation to the amount of toner adhered on the photoreceptor and the laser power shown in FIG. It is not possible to correct the change in the amount of toner adhered when the humidity changes.

[0011]

In the prior art, since the laser power at the time of laser power modulation is controlled to a multi-stage fixed value, a different power is used in the electrophotographic printing apparatus for each multi-stage laser power at the time of laser power modulation. The change in the amount of toner adhesion due to the influence of the temperature and humidity cannot be corrected, and the gradation property is deteriorated.

It is an object of the present invention to provide a method for controlling the temperature in an electrophotographic printing apparatus which is different for each multi-step laser power during laser power modulation.
The purpose of the present invention is to provide a variable control means of a laser power set value of a semiconductor laser for correcting a change in the amount of toner adhesion due to the influence of humidity, thereby simplifying a laser driver circuit and a control circuit of the laser driver circuit to reduce cost. And to perform fine laser power variable control with a small circuit.

[0013]

In order to achieve the above-mentioned object, in the present invention, an arithmetic means such as a microcomputer variably controls a laser power set voltage to variably control a laser power set value.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a diagram schematically showing the laser power variable control according to the present invention. FIG. 1 shows a D / A converter L2 and a D / A converter which can output the laser power set voltage output from the reference voltage source of the laser driver and input to the comparator in the laser power modulation control system of FIG. By using the output of the converter H3, a laser power modulation control system capable of variably controlling the multi-step laser power at the time of laser power modulation is configured.

The microcomputer 1 uses the temperature and humidity information from the temperature / humidity sensor 25 to change the laser power from the initial adjustment value by one.
If it is determined that it is desired to increase by 0%, the D / A converter L
By outputting data corresponding to a 10% increase in the two outputs to the D / A converter L2, the laser power setting voltage V
rL6 can be increased by 10%, and the output of the laser power Po19 can be increased by 10%.

The D / A converters and the laser drivers are provided by the number of the multi-step laser power setting values used for the laser power modulation, and are connected in parallel to the semiconductor laser 16 so that the multi-step laser power during the laser power modulation can be reduced. Laser power variable control can be performed.

The number of laser power variable control steps is D / A
It is determined by the number of digital input bits of the converter L2 and the D / A converter H3. When an 8-bit input D / A converter is used, 256-step laser power variable control is possible.

[0019]

As described above, according to the present invention, the laser power can be variably controlled with a small-sized and low-cost circuit. The change in the amount of adhered toner due to the influence of the temperature and humidity can be corrected, and high image quality of the electrophotographic printing apparatus can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing one embodiment of a conventional laser power modulation control circuit.

FIG. 3 is a diagram illustrating a relationship between a toner adhesion amount on a photoconductor and a laser power.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Microcomputer, 2 ... D / A converter L, 3 ... D / A converter H, 6 ... Laser power setting voltage VrL, 15 ...
Hold capacitors H, 16: semiconductor laser, 17: laser diode, 18: photodiode, 19: laser power Po, 20: monitor current Im.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) 9A001 (72) Inventor Shoka Kawano 1060 Takeda, Hitachinaka-shi, Ibaraki F-term in Hitachi Koki Co., Ltd. (Reference) 2C362 AA54 AA57 AA59 AA61 CA10 2H027 DA13 DA14 EA02 EB03 EC06 EC20 EF09 2H076 AB05 AB76 DA10 DA17 5C074 AA05 BB03 CC26 DD08 EE03 GG02 5F073 BA07 FA01 GA12 GA14 GA20 GA24 9A001 BB06 HH34 JJ35 KK42

Claims (2)

[Claims] 1. An electrophotographic apparatus using a laser driver having a laser power initial adjusting means and a laser power varying means and a semiconductor laser driven by the laser driver, wherein the laser driver has a laser power at a multi-step laser power set value. A laser power control device for an electrophotographic apparatus, characterized in that a variable means for performing modulation and arbitrarily changing the set value of the laser power for all the multi-stage laser power set values is provided. 2. A laser power control device for an electrophotographic apparatus according to claim 1, further comprising a laser power variable means for variably controlling an output of a temperature and humidity sensor provided in the electrophotographic apparatus.