JPS62116071A - Intensity modulation adjusting device for semiconductor laser in laser beam printer - Google Patents

Abstract

PURPOSE:To automatically adjust the printing density by providing a means to control the driving electric current of a laser to the value corresponding to a prescribed initial value and a modulating intensity value setting means of the laser, and controlling the light emitting strength based upon the adding result of the modulating intensity and the initial value. CONSTITUTION:Except during the scanning printing, by a control means 101, the detecting light emitting strength value of a laser 100 is compared with the initial value set before hand, and the driving electric current value of the laser 100 is controlled to an initial driving electric current value corresponding to the initial value. By a setting means 102, the modulating intensity value for adjusting the light emitting strength is set, by an arithmetic means 103, the set modulating intensity value is added to the above-mentioned initial value and the driving electric current control value is calculated. A control means 104 controls the light emitting strength of the laser 100 based upon the calculated riving electric current control value. Thus, the reference value of an auto power control (APC) circuit can be kept as it is in addition, the density of the optional printing can be set.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Technical Field The present invention relates to an intensity modulation adjustment device for a semiconductor laser in a laser beam printer.

b. Prior art and its problems Recently, a laser beam modulated based on image information such as figures, characters, etc. is exposed and scanned onto a charged photoreceptor to form an electrostatic latent image, which is then developed (developed). , transcription.

A so-called laser beam printer (rLB) obtains a hard copy of image information through a copying process such as fixing.
(abbreviated as PJ) is becoming more and more popular, and the practical use of compact and low-cost LBPs using semiconductor lasers is particularly popular.

By the way, in LBP using this semiconductor laser (laser diode), if you want to change the print density (image density) of a hard copy, the conventional method is generally as follows.6 In other words, the semiconductor laser drive device in LBP ,
Detects the emission intensity of the semiconductor laser, compares the detected emission intensity value with a reference value (reference voltage), and drives the semiconductor laser so that the emission intensity corresponds to the reference value based on the comparison result. It is equipped with an auto power control (APC) circuit that feedback controls the current value, and by operating the dial (volume) that sets the reference value in this APC circuit, the emission intensity of the semiconductor laser can be varied and the concentration can be adjusted. Shall we go?

The development bias in the post-exposure development process was controlled by operating an adjustment dial.

However, such conventional adjustment specifications have the following problems.

In other words, it is not only undesirable for the user to arbitrarily change the comparison reference value in the APC circuit from the standpoint of the design and operation of the APC circuit. However, after completing printing of one page of hard copy, the density must be set before starting printing of the next page, resulting in a longer cycle time.

Note that when it is desired to vary the printing speed, it is also necessary to vary the emission intensity of the semiconductor laser, and this case also has the same problem as the case of varying the density.

C0 Purpose This invention has been made in view of the above background, and in the laser beam printer as described above, as shown in FIG. A first control means 101 that compares a detected emission intensity value with a preset initial value and controls the drive current value of the semiconductor laser 100 to an initial drive current value corresponding to the initial value; and a first control means 101 that controls the emission intensity of the semiconductor laser 100. a setting means 102 for setting a modulation intensity value for a drive current control value, a calculation means 103 for calculating a drive current control value by adding the modulation intensity value set by this setting means 102 to the above-mentioned initial value, and a drive current control value calculated by a laser beam. The above-described conventional problems are solved by providing an intensity modulation adjustment device for a semiconductor laser that includes a second control means 104 that controls the emission intensity of the semiconductor laser 100 based on a current control value. be.

d. Structure of the Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIG. 2 and subsequent drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention.

In the figure, 1 is a control unit of a laser beam printer (LBP), including a control section 2 and an intensity modulation control section 3.
, comparator 4, D/A converter 5, buffer (voltage follower) 6, bin photodiode PD, resistor R□, initial value (
It is composed of a variable power supply VE for setting a reference value), a resistor R21, a PNP type transistor Trl for intensity modulation, a semiconductor laser (laser diode) LD, and an NPN type transistor Tr2 for print modulation.

The control unit 2 has a system configuration including a microcomputer and the like, and is in charge of overall control of the LBPI.

The intensity modulation control unit 3 includes a central processing unit (CPU) 30
, program memory (ROM) 31, data: Amo IJ
(RAM)32. And input/output equipment! (Ilo)33
It consists of a microcomputer consisting of 31 ROMs, etc.
When the CPU 30 timely executes a program to be described later that is stored in advance in
, and performs various functions related to the second control means 104.

Regarding the function of the setting means 102, strictly speaking, the control unit 2, an external device 7 and a keyboard 8, which will be described later, are also constituent elements, and the first and second control means 1
01 and 104, the input system around the comparator 4 and the output system after the D/A converter 5 are also constituent elements.

Then, between this intensity modulation control section 3 and the above-mentioned control section 2, an enable signal S, which will be described later, a modulation intensity value reading start signal S2. Synchronization signal S1. Modulation intensity value data S4
, comparison sampling signal S, and other signals are exchanged.

The comparator 4 has an initial value (initial voltage value) Vref set in advance (for example, set by the manufacturer at the time of factory shipment) by the variable power supply VE input to its non-inverting input terminal pin photodiode PD
The current Im corresponding to the emission intensity of the semiconductor laser LD detected by is compared with the detected emission intensity value Vx which is converted into a voltage value using a resistor R.
When ref<VX, a comparison signal S0 of ``L'' is output.

The comparison signal S0 of this comparator 4 is input to l1033 in the intensity modulation control section 3.

Incidentally, when setting the initial value Vref, it is assumed that the initial value Vref is not set to a required value, but is gradually increased from a fairly low value.

Next, the D/A converter 5 receives a drive current control value sy, which will be described later, output from l1033 in the intensity modulation control unit 3.
is converted into a drive current control voltage value vy from digital to analog.

Resistor R2, emitter and collector of transistor Tr,
The semiconductor laser LD is connected in series between +Vcc and ground in the above order, and a drive current control voltage value Vy is applied to the base of the transistor Tr1 via the buffer 6.

The semiconductor laser LD is connected in parallel between the collector and emitter of a transistor Tr2, and the modulation signal MD output from the control section 2 is applied to the base of the transistor Tr2.

Therefore, when the transistor Trz is off, a drive current ILD corresponding to the drive current control voltage value vy flows through the semiconductor LD, and a corresponding laser beam is output.When the transistor Tr2 is on, the output of the laser beam is stopped. Ru.

Next, the external device 7 transfers various data such as print image data and modulation intensity value data according to the present invention to the control unit 2 in the LBPI.

The keyboard 8 is used to set modulation intensity values, etc., and is used when the LBP user sets the density of the required page, the density of all pages, the density of each page, etc. of the hard copy obtained by LBPI. Manipulate.

e. Effects of the Embodiment The effects of the embodiment configured as described above will be explained below with reference to FIGS. 3 to 6.

It is assumed that the initial value Vref used as a comparison standard for the comparator 4 in LBPI is set in advance to a required value by the variable power supply VE.

First, the LBP user operates the keyboard 8 to input a modulation intensity value (for example, 6-bit data length data in this embodiment) in order to determine the print density of the hard copy of the document that will be printed using LBPI. Set.

Examples of this setting specification include, for example, a setting specification in which all pages of the hard copy have a uniform density, a setting specification in which only the required page has a different density from other pages, etc. LBP users can set the setting specification according to their needs. Set with .

The modulation intensity value data set by the keyboard operation is transferred and stored in a required data storage area in the control unit 2 of the external device 7 to the LBP.

Incidentally, a standard modulation intensity value is written in advance in the data storage area of the external device 7 or the control unit 2.

When LBP users do not particularly perform keyboard operations,
The standard value may be used.

Next, when the LBPI is activated, the CPU 30 in the intensity modulation control section 3 performs necessary initialization processing, and then proceeds with the processing in order from the first step in FIG.

First, "0" is written in the register C for output to the D/A converter S, and then "o" in the register C is output to the D/A converter 5 as the drive current control value Sy.

As a result, due to the action of the D/A converter 5 and the buffer 6, the transistor Tr1 receives a predetermined weak drive current IL.
Play D. However, at this time, for example, the control unit 2 is outputting a modulation signal MD that turns on the transistor Tr, so the semiconductor laser LD does not emit light.

Next, the CPU 30 receives an enable signal S from the control unit 2.
1 has risen to high level 1H' or not, and if S is at low level ``L'', it is set to high level''
Wait until Sl rises to H', for example, as shown in Figure 6 (a).
When the signal rises to the high level 1H' at time t□ shown in FIG. 2, the process proceeds to the next step.

In the next step, it is checked whether the modulation intensity value reading start signal S2 from the control unit 2 has risen to a high level 1H', and if S is a low level ""L', wait until it rises to a high level %H'. , S2 rises to a high level 1H' at time t2 shown in FIG. 6(b), for example, and the process moves to execution of the input subroutine of the first step.

This input subroutine is programmed, for example, as shown in FIG. 4, and when the input subroutine is called, the data length value "n
” (n=6 in this embodiment) is written.

After a certain period of time after the synchronization signal S in l1033 and the output port are raised from low level "L' to high level 1"1, from high level 1H' to low level 1L'
, a single sync signal S is generated and output to the control unit 2, and in synchronization with the fall of the sync signal S, the control unit 2 outputs a hard copy of the document to be printed. The bit data (initially, the data of the 6th bit among the 1st to 6th bits) indicated by the value of the register D in the modulation intensity value data that determines the density of the first page is read into the accumulator Ace.

Then, in the next step, the accumulator Ace becomes 11'.
If it is '1', set the bit indicated by the value of register D in the register for storing the modulation intensity value to '1'.
%0", reset the bit indicated by the value of register D in register B to 10#, increment the value of register D by one, and then check whether the value of register D has become O. If it is not yet O, the process returns to step 11033 in which the synchronizing signal S and the output report are raised from low level 1L' to high level 1H', and each process subsequent to this process step is repeated.

By repeating the above process until the value of register D becomes 0, the modulation intensity value 54 (6-bit data) for determining the density of the first page is transferred from the control section 2 to register B.
, the process of the principal's subroutine is completed, and the process returns to the main routine of FIG.

The process of the above input subroutine is shown in Figure 6 (c).
The modulation intensity value data S4 of the first page, which is shown in FIG.

Returning to FIG. 3, when the CPU 30 completes the execution process of the input subroutine, in the next step it checks whether the modulation intensity value reading star 1 signal S2 has fallen to the low level 1L", and as shown in FIG. At the point shown in (b), S2
Proceeds to the next step only when falls to the low level "L#".

In the next step, it is checked whether the comparison sampling signal S from the control section 2 has risen to the high level 1H', and the signal SS has risen to the high level 'IH' at time t4 shown in FIG. 6(E). Only when it starts up does it move on to the next step of executing the comparison subroutine.

The control unit 2 lowers the modulation signal MD to the base of the transistor Tr at the time t when the comparison sampling signal S to the intensity modulation control unit 3 is raised to a high level ``H''. The level is set to 11 L 71 and the transistor Tr2 is turned off.

As a result, the semiconductor laser LD is driven by the aforementioned weak drive current I to emit light.

The comparison subroutine is programmed, for example, as shown in FIG. 5, and when the comparison subroutine is called, it is first checked whether the comparison signal s0 of the comparator 4 is at a high level 1H".

As described above, at the time of this comparison, the semiconductor laser LD emits light using the weak drive current ILD, so a current Im corresponding to the light emission flows through the pin photodiode PD.

Therefore, the light emission intensity value Vx (voltage value) based on the current Im corresponding to the light emission intensity of the semiconductor laser LD driven by the weak drive current ILD is input to the inverting input terminal O of the comparator 4. It is compared with the initial value Vref input to the inverting input terminal ■.

In this initial state, the circuit is designed so that V ref ) V x, so the comparison signal S0 is at a high level 1H".

Therefore, at this time, as a result of the level check of So, the CPU 30 determines the value of register C (at this initial stage, it is "0").
) is incremented by +1, the result is output to the D/A converter 5 as the drive current control value sy, and then the process returns to the main routine.

Then, in the main routine, the above comparison subroutine is repeatedly called and executed until the comparison sampling signal S5 from the control unit 2 falls to the low level "'L" at the time t shown in FIG. 6(E), for example. It looks like this.

Therefore, as the value of register C is incremented by +1, the drive current control voltage value vy
As the voltage level increases, the emission intensity of the semiconductor laser LD increases.

Then, the emission intensity of the semiconductor laser LD increases, the emission intensity value Vx increases, and finally V ref < v x and the comparison signal S0 becomes low level 'L'.

Then, in the comparison subroutine described above, the CPU 30 decrements the value of the register C by 1, and outputs the result as the drive current control value sy to the D/A converter 5 sequentially. Against 1. -1.
If enough time is secured, Vx is V x =
V ref and the value of register C is the initial value V ref
The drive current ILD falls within the value corresponding to f, and the drive current ILD is the initial value V
The initial drive current value corresponds to ref.

In this way, the comparison sampling signal S from the control unit 2,
from time t4 when is at high level 1H' to time t,
In other words, during the period other than laser beam scanning printing,
The drive current I of the semiconductor laser LD is determined by comparing the detected emission intensity value Vx of the semiconductor laser LD with a predetermined initial value Vref.
The so-called auto power control (APC) controls the LD to an initial drive current value corresponding to the initial value Vref.
) is performed (corresponding to the first control means). Returning to FIG. 3, the comparison sampling signal S is determined as shown in FIG. 6 (
From high level 1H# to low level 1L at time t of e)
', the CPU 30 first stores the value of the register C (here, the value corresponding to the initial value V ref ) in the accumulator Acc, and then stores the value of the register C in the accumulator Acc.
The value of the first hardcopy stored in the register
Modulation intensity value data S, h (ro 11
000J) is added (corresponding to the calculation means).

Then, the CPU 30 sets the added value of the accumulator Acc as the drive current control value sy, and outputs it to the /A converter 5. Therefore, the drive current ILD of the semiconductor laser LD is determined by the drive current control voltage value vy based on the added value of the accumulator Acc. 6 (Fig. 6).
The luminescence intensity corresponding to the initial drive current value shown in (g). A laser beam having an emission intensity L1 obtained by adding the modulation intensity value S4 (ro 11000J)L of the first page and the corresponding increment ΔL1 is output.

Then, as shown in FIG. 6(E), after a certain period of time after the comparison sampling signal S falls from the high level "H' to the low level "L" at time L5, the control unit 2 As shown in (f), the printing control mechanism (not shown) is controlled to start printing scanning (including controlling the transistor Tr2 on and off using the modulation signal MD), so the printing density of the resulting hard copy is as follows: Initial value Vref and 1st W+71st modulation intensity value S, (rollooJ')
I: Therefore, the concentration is determined.

That is, during laser beam scanning printing for the first page, the modulation intensity value S4 (1'011000) of the first page read from the control unit 2 before starting printing of the first page is set to the initial value Vref.
So-called open loop control is performed to control the emission intensity of the semiconductor laser LD based on the drive current control voltage value vy corresponding to the sum of J) (corresponding to the second control means).

Note that in the auto power control that is performed at times other than the laser beam scanning described above, a circuit (not shown) that compensates for output changes due to temperature changes in the semiconductor laser LD functions, but during the open loop control described above, Since the circuit will not function, take measures to keep the temperature constant, such as installing a heat sink with sufficient heat dissipation on the semiconductor laser LD, so that the temperature of the semiconductor laser LD does not change during printing (for example, for about 10 seconds). It is good to give it.

Return to Figure 3.

After outputting the calculated value for determining the print density of the first page, the CPU 30 checks whether the enable signal S1 from the control unit 2 has fallen from the high level 1H' to the low level 1L#, and then If so, write "o" into register C, output the value of register C to D/A converter 5, and then return to the first step of the main routine.

At this time, the control section 2 outputs a modulation signal MD that turns on the Tr2, and stops the semiconductor laser LD from emitting light.

On the other hand, if the enable signal S has not fallen to the low level 1L' as shown in FIG.
In the next step, it is checked again whether the modulation intensity value reading start signal S2 has risen to the high level 'H', and if it has not risen, it waits until it rises.

Then, S2 is at a high level at 1 s in Figure 6 (b).
When it rises to 'H', the input subroutine of the next step, which is exactly the same as the steps from the input subroutine described above to Ace→D/A, starts from the input subroutine including the step 8.
By sequentially executing the steps, the modulation intensity value reading start signal S2 is at a high level of 1H# from time t6 to time L7, that is, during printing of the first page, the control unit 2 reads the modulation of the second page. Intensity value data S4 (rlooo.

From the time point t in FIG. 6(E) when the comparison sampling signal S rises from the low level 'L' to the high level 1H', the light emission amount of the semiconductor laser LD is measured as shown in FIG. Mustard as shown in (g). From the time when S falls to the low level 'L' at time 9 in FIG. 6(E), the amount of light emitted from the semiconductor laser LD becomes less than L as shown in FIG. 6(G). , =L, +ΔL2(ΔL
2: an increment corresponding to the second modulation intensity value S4 (rlooooOJ)).

The printing on the first page is as shown in FIG.

The process ends at any point between time t7 and time t.

Then, the above-mentioned 8th step A c c − + D
/ After completing the process A, the enable signal S1 is activated again.
Returning to the process of checking whether or not S has fallen to the low level 'L', the subsequent processes are repeated until S□ falls to the low level 'L#'.

In addition, in FIG. 6(d), the modulation intensity value data S4 ("
001111'') is read from the control unit 2.

According to the above embodiment, it is not only possible to set the density of a hard copy without changing the comparison reference value (initial value Vref) as in the conventional case, but also to set the density in advance when you want to change the density of each page. Since the density of each page can be set in advance, or the density of the next page can be set during printing, this is not only very desirable in terms of APC circuit design and operation, but also does not lengthen the cycle time for hard copy creation. It ends up being

Of course, if you want to change the printing speed for each page, you can keep the density of the hard copy constant regardless of the change in printing speed by changing the modulation intensity value data S4 according to the amount of change in printing speed. I can do it.

In the above embodiment, the modulation intensity value is set using the keyboard 8. However, the present invention is not limited to this, and if another electronic device is connected to the external device 7, Modulation intensity value data may be set and output from the electronic device.

Finally, a specific numerical example of the modulation intensity value during the light amount control of the semiconductor LD will be shown.

For example, if the light amount is controlled to be OmW to 4mW.

In the case of 8-bit D/A, it is 2565 tep, and 1 bit
The resolution is 15.625 μW per unit.

Therefore, if the intensity during intensity modulation is 1 mW, the modulation intensity value data may be <6 bits as in the example (15°625μWX
64=1mW).

Specifically, if the drive current control flE value S y becomes rloooooooOJ and the semiconductor laser LD is driven at 2 mW based on the initial value V ref <during APC control, for example, the first page 2mW, second page 2.3mW
, when you want to control the third page at 2.7mW, r
ooooooOJ, roloollJ while printing 1 page,
2nd page printing 4:, ll011o1'' modulation intensity value S4
may be read out from the control unit 2.

f. Effects As described above, according to the intensity modulation adjustment device for a semiconductor laser in a laser beam printer according to the present invention,
Not only does it not require changing the reference value in the APC circuit, but it is also possible to set the density of the hard copy arbitrarily, which is not only very desirable in terms of the design and operation of the APC circuit, but also makes it easier to create the hard copy. Cycle time does not become unnecessarily long.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. FIG. 2 is a block diagram showing an embodiment of the invention. FIG. 3 is a flow diagram of a program executed by the CPU 30 in FIG. 2. FIG. 5 is a flow diagram of a program for the input subroutine of FIG. 3. FIG. 6 is a timing diagram for explaining the operation of FIG. 3. 1... Laser beam printer (LBP) 2.
... Control section 3 ... Intensity modulation control section 4 ... Comparator 5 ... D/A converter 6 ... Buffer 7. ... External device 8 ... Keyboard 30 ... Central processing unit (CPU) 31 ...
...Program memory (ROM) 32...Data memory (RAM) 33...Input/output device (I
lo) R1, R2... Resistor Tr, Tr2... Transistor LD...
・・Semiconductor laser PD・・・・・・Bin photodiode patent applicant
Asahi Optical Co., Ltd. Representative Matsumoto Withdrawal Agent Patent Attorney Tatsuo Itami Figure 1 Proceedings Amendment Written July 23, 1986

Claims (1)

[Scope of Claims] 1. In a laser beam that scans a laser beam of a semiconductor laser modulated based on image information such as figures and characters to obtain a hard copy of the image information, except during the laser beam scanning printing. a first control means that compares the detected emission intensity value of the semiconductor laser with a preset initial value and controls the drive current value of the semiconductor laser to an initial drive current value corresponding to the initial value; a setting means for setting a light emission intensity value for adjusting the light emission intensity of the semiconductor laser; a calculation means for calculating a drive current control value by adding the modulation intensity value set by the setting means to the initial value; and the laser beam scanning. a second control means for controlling the emission intensity of the semiconductor laser based on the drive current control value calculated by the calculation means during printing; Intensity modulation adjustment device.