JPH03202367A - Device for controlling light quantity for laser oscillator - Google Patents

Abstract

PURPOSE:To avoid the influence of noise without consuming excessive toner and without using a high speed A/D converter or a high speed microcomputer by holding a plurality of times the results of comparison between light quantity detection signals and reference signals and then setting drive current of a laser oscillator depending on the results of comparison when said results held in the holding means agree with each other. CONSTITUTION:A latch signal generating means 19 generates a plurality of latch signals 23 outside a recording region based on beam detection signals from a beam detecting means 18. A latch circuit 20, as a holding means, latches the results of comparison of a comparing means 17 a plurality of times in conformity with the timing of latch signals 23. When a plurality of results of comparison having been latched by the circuit 20 agree with each other, a light quantity control means 21, which may include a microcomputer, sets drive current of a drive means 22 depending on said results of comparison.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a light amount control device for a laser oscillator used in an image forming apparatus such as a laser printer or a digital copying machine.

(Prior Art) Recently, an electrophotographic laser printer has been developed that prints by scanning exposure using a laser beam output from a laser oscillator and an electrophotographic process.

In this type of laser printer, a semiconductor laser oscillator is used as a laser oscillator for obtaining a laser beam. Generally, the amount of light from a semiconductor laser oscillator is very unstable with respect to temperature, so the amount of light from the semiconductor laser oscillator is usually stabilized using a light amount control device or the like.

There are various methods for controlling the light amount of a semiconductor laser oscillator, but an inexpensive method uses a well-known general-purpose microcomputer (hereinafter referred to as a microcomputer) with a built-in A/D converter to control pages and pages without image recording. A semiconductor laser oscillator is caused to emit light continuously between the pages, and while the semiconductor laser oscillator is emitting light, the light intensity of the semiconductor laser oscillator is detected by a light intensity detector, the detected light intensity is read by an A/D converter, and the read light intensity and a reference signal are detected. The amount of light from the semiconductor laser oscillator was stabilized by comparing the two and setting the driving current of the semiconductor laser oscillator according to the comparison result.

(Problem to be solved by the invention) Conventionally, a semiconductor laser oscillator is made to emit light continuously between pages on which no image is recorded to stabilize the amount of light from the semiconductor laser oscillator, so for example, a reversal development method is applied. In image forming apparatuses such as laser printers and digital copying machines, there is a problem in that development is performed within the recording area, resulting in excess toner consumption.

Another method to solve this problem is to make the semiconductor laser oscillator emit light outside the recording area and stabilize the amount of light from the semiconductor laser oscillator while emitting light. Normally, the time for emitting light is short, and the amount of light from the semiconductor laser oscillator is detected by a light amount detector, and the detected amount of light is read by the A/D converter of a general-purpose microcontroller with a built-in A/D converter.
Since the D conversion time is too slow, a high-speed A/D converter is required, which is expensive. Furthermore, the process from reading the detected light amount to setting the drive current of the semiconductor laser oscillator must be performed by the microcomputer at high speed.
A high-speed microcontroller is required.

In addition, when the semiconductor laser oscillator and its light intensity control unit are located far apart, the analog line between the light intensity detector that detects the light intensity of the semiconductor laser oscillator and the A/D converter becomes long, so noise may be affected. It becomes easier to receive.

Furthermore, the higher the speed of a laser printer or digital copying machine, the shorter the beam scanning period, which shortens the light emission time of the semiconductor laser oscillator outside the recording area, which is even more disadvantageous.

Therefore, the present invention provides a method that eliminates the need to consume excess toner.
Even in high-speed laser printers and high-speed digital copying machines, there is no need to use high-speed A/D converters or high-speed microcomputers, and there is a light amount detection means that detects the light amount of the laser oscillator and a light amount control section for the laser oscillator. An object of the present invention is to provide a stable light amount control device for a laser oscillator that is not affected by noise even when the distance between the laser oscillator and the laser oscillator is large.

[Configuration of the Invention (Means for Solving the Problems) A light amount control device for a laser oscillator according to the present invention includes a scanning means for scanning a surface to be scanned by scanning a laser beam output from a laser oscillator, and a scanning means for scanning a surface to be scanned by scanning a laser beam outputted from a laser oscillator; a driving means for driving an oscillator with current; a light quantity detecting means for detecting the light quantity of the laser oscillator; a comparing means for comparing a light quantity detection signal of the light quantity detecting means with a preset reference signal; and a scanning means for scanning by the scanning means. beam detection means for detecting the position of the laser beam that has been detected; holding means for holding the comparison results of the comparison means a plurality of times based on the beam detection signal of the beam detection means; and a plurality of comparisons held by the holding means. and a light amount control means for controlling the light amount of the laser oscillator by setting the drive current of the drive means according to the comparison result when the results match.

(Function) The comparison results of the comparison means for comparing the light amount detection signal and the reference signal based on the beam detection signal are held in the holding means multiple times, and when the plurality of held comparison results match,
By setting the driving current of the laser oscillator according to the comparison result, the amount of light from the laser oscillator is controlled.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an outline of a light amount control device for a semiconductor laser oscillator according to the present invention. In the figure, a polygon mirror 9 scans a laser beam 12 output from a semiconductor laser oscillator 11 onto a drum-shaped photoreceptor 10 serving as an image carrier in an image forming apparatus in the direction of an arrow.

The laser beam 13 scanned by the polygon mirror 9 is detected by the beam detection means 18 outside the recording area (outside the image forming area) of the photoreceptor 10.

The driving means 22 inputs a modulation signal output based on the beam detection signal detected by the beam detecting means 18, and drives the semiconductor laser oscillator 11 with current to record information at a predetermined position on the photoreceptor 10.

The light amount detection means 15 detects the amount of light of the laser beam 14 output from the semiconductor laser oscillator 11.

The comparison means 17 compares the detection signal of the light amount detection means 15 and the reference signal from the reference signal generation means 16.

The latch signal generating means 19 generates a plurality of latch signals 23 outside the recording area based on the beam detection signal from the beam detecting means 18. The latch circuit 20 serving as a holding means latches the comparison result of the comparison means 17 a plurality of times at the timing of the latch signal 23.

The light amount control means 21 is mainly composed of a microcomputer, for example, and when the plurality of comparison results latched by the latch circuit 20 match, the light amount control means 21 controls the driving means 22 according to the comparison result.
By setting the drive current, the amount of laser beam output from the semiconductor laser oscillator 11 is uniformly controlled.

FIG. 2 is a block diagram showing in detail a part of the light amount control device for a semiconductor laser oscillator according to the present invention. In the figure, 30 is a semiconductor laser oscillator, which is composed of a laser diode 31 that outputs a laser beam, and a monitoring photodiode 32 that detects the intensity of the laser beam output from the laser diode 31. The laser diode 31 is driven with a constant current by a constant current circuit composed of a transistor 33 and a resistor 34.

The base of the transistor 33 is connected to the output of the D/A conversion circuit 35 and the collector of the transistor 36.

The drive current flowing through the semiconductor laser oscillator 30 is proportional to the output voltage of the D/A conversion circuit 35.

The transistor 36 repeatedly turns on and off in response to a laser modulation signal output from the laser modulation control circuit 37, thereby modulating the laser diode 31. In this case, the laser diode 31 turns off when the laser modulation signal is at a low level and emits light at a low level. The D/A conversion circuit 35 converts the digital value of the laser drive current output output from the human output register 38 into an analog voltage.

On the other hand, a current proportional to the beam intensity of the laser diode 31 flows through the monitor photodiode 32 . Resistor 39 converts the current flowing through photodiode 32 into voltage. The converted voltage is applied to an operational amplifier 40 and a resistor 41.
, a variable resistor 42, which performs non-inverting amplification.

Here, the variable resistor 42 is used to adjust the amplification factor, and its purpose is to correct differences in current characteristics flowing through the monitoring photodiode 32 with respect to the beam intensity of the laser diode 31 due to variations in the semiconductor laser oscillator 30. .

The output of the operational amplifier 40 is input to one side input terminal of the comparator 43, and the reference voltage Vre inputted to the + side terminal
It is compared with f2. This reference voltage Vref2 sets the target light intensity of the laser diode 31. When the output of the operational amplifier 40 is less than Vref:2, it is assumed that the target light intensity has not been reached, and the output of the comparator 43 becomes high level, and the output of the operational amplifier 40 becomes high level. When it exceeds Vref2, the target light amount has been reached and the output of the comparator 43 becomes low level.

The comparison result of the comparator 43 is latched into latch circuits 44 and 45. The latch circuits 44 and 45 latch the output of the comparator 43 twice in synchronization with the input latch pulse output from the selector 46, and the outputs of the latch circuits 44 and 45 are input to the human output register 38, Processing is performed by a CPU (not shown) that controls the entire printer.

The selector 46 is a selector that selects the input latch pulse A output from the human output register 38 and the input latch pulse B output from the laser modulation control circuit 37 using a latch pulse switching signal output from the human output register 38, When the latch pulse switching signal is at low level, manual latch pulse A is selected, and when high level, manual latch pulse B is selected.

A beam detector 47 detects the position of the scanned laser beam 13, and uses a bin diode, for example. When the scanned laser beam 13 is incident, a current proportional to the intensity of the incident laser beam flows through the bin diode 47. Resistor 48 converts the current flowing through bin diode 47 into voltage. The converted voltage is input to one side terminal of the four comparators, compared with the reference voltage Vrefl input to the + side terminal, and inputted to the laser modulation control circuit 37 as a negative pulse beam detection signal. .

In response to the continuous pulse output of the beam detection signal, the laser modulation control circuit 37 sets the beam detection ready signal to the input/output register 38 as a beam detection ready signal from a low level to a high level (see e+g in FIG. 3). ).

The latch pulse switching signal output from the input/output register 38 outputs a low level when the beam detection ready signal is at the L low level, and outputs a high level when the beam detection ready signal is at the high level.
(See 3rd diagram).

When the beam detection signal is output, the laser modulation control circuit 37 outputs an input latch pulse B outside the recording area based on the beam detection signal (see FIG. 3). Further, this input latch pulse B is frequency-divided by two in a frequency dividing circuit 50 and input as an interrupt signal to the interrupt input of the CPU (see FIG. 3, n). That is, when two input latch pulses B are output, the output of the comparator 43 is latched twice in the latch circuits 44 and 45, and an interrupt is issued to the CPU at the timing when the second time is latched.

In FIG. 2, reference numerals 51 and 52 denote internal buses of the CPU, each of which is connected to a CPU (not shown). Further, 53 is an interface signal, which is connected to a printer control circuit (not shown).

Next, the operation will be explained with reference to the timing chart shown in FIG. 3 and the flow chart shown in FIG. 4. first,
When the power is turned on, the fixing heater starts heating.
) Initialize the laser drive current output from the input/output register 38 (S2). Next, the input latch pulse A is selected by the selector 45 using the latch pulse switching signal output from the input/output register 38 (S3).

Next, the laser modulation signal output from the laser modulation control circuit 37 is forcibly turned on (S4). Next, the laser drive current is incremented (S5) and output from the input/output register 38, and then D/A converted by the D/A conversion circuit 35, and a current starts flowing to the laser diode 31.

After a predetermined time delay (S6), when the input latch pulse A is output from the input/output register 38 (S7), the comparator 43
The comparison result is latched in the latch circuit 44. Next, it is determined whether the comparison result latched by the latch circuit 44 has reached the target light amount (S8). Here, the target light amount means that the output voltage of the operational amplifier 40 is equal to the reference voltage V of the comparator 43.
This is when ref2 is reached, and at this time the output of the comparator 43 changes from "1" to °O.

If the target light amount has not been reached in step S8, the process returns to step S5 and is repeated until the target light amount is reached. Step S8
When the target light amount is reached, the laser drive current value is stored in a RAM (not shown) (S9), and the laser modulation signal is forcibly turned off (S10).

The loop continues until the fixing heater becomes ready in step S11, and when the fixing heater becomes ready, it waits for a print command (
S12). When a print command comes, the mirror motor is turned on (513), the laser drive current value stored in the RAM in step S9 is read out (514), and 1/n of the read laser drive current value is output from the human output register 38 ( S15).

Next, the laser modulation signal is forcibly turned on (S16), and the laser drive current is incremented (S17).

After a predetermined time delay (S18), the laser modulation control circuit 3
It is determined whether the beam detection ready signal output from 7 is beam detection ready (S19). Here, beam detection ready means when the beam intensity of the scanning beam incident on the beam detector 47 exceeds the reference voltage Vrefl of the comparator 49 and the beam detection signal is continuously generated (Fig. 3e,
(see g).

If the beam detection is not ready in step S19, the process returns to step S17 and is repeated until the beam detection is ready.

When the beam detection becomes ready in step S19, the laser modulation signal is forcibly turned off (S20). The laser modulation control circuit 37 outputs a beam detection ready signal, and at the same time emits a laser modulation signal in a sampled manner outside the recording area based on the beam detection signal, and similarly outputs a manual latch pulse B outside the recording area based on the beam detection signal. Output (Figure 3 f,
(see l).

Next, in step S21, the selector 46 selects the manual latch pulse B using the latch pulse switching signal output from the input/output register 38 (see the third diagram).
. Next, the CPU interrupt is canceled (S22), and the loop is repeated until the input latch pulse B of the interrupt signal is generated (323).

Here, when an interrupt signal is generated, the comparison result of the comparator 43 is transferred to the latch circuits 44 and 45 by the human latch pulse B.
latched to.

Next, it is determined whether or not the comparison results latched by the latch circuits 44 and 45 match (524). If the comparison results match, the process advances to step S25, and if they do not match, the process returns to step 523. In step S25, the latch circuit 44
．． It is determined whether the comparison result latched in step 45 has reached the target light amount.

When the target light amount has not been reached, the laser drive current is incremented (S26) and output to the D/A conversion circuit 35.

Thereafter, the process returns to step 523 and is repeated until the target light amount is reached. When the target light amount is reached, the laser drive current is decremented (S27), and step S23+
,:return.

After reaching the target light intensity, the light intensity control of the semiconductor laser oscillator 3o is continued every time an interrupt signal is generated.

In this way, the latch signal generation means generates a plurality of latch signals outside the recording area based on the beam detection signal, and the comparison results of the comparison means are latched multiple times into the latch circuit using the latch signals. When the results of the comparisons match, the drive current of the semiconductor laser oscillator is set according to the comparison result, thereby controlling the amount of light of the semiconductor laser oscillator M.

This prevents the semiconductor laser oscillator from emitting light between pages on which no image is to be formed, so that excess toner consumption can be prevented, especially in those using the reversal development method.

Furthermore, since a high-speed A/D converter is not required, the cost can be reduced.

In addition, even if the time during which the semiconductor laser oscillator can emit light outside the recording area is shortened, it is possible to read the comparison results reliably. The drive current can be set in ample time.

Therefore, a general-purpose microcomputer can be used and is inexpensive, and high-speed machines can also be used.

Furthermore, even if the light intensity detector that detects the light intensity of the semiconductor laser oscillator is located far away from the light jl control section of the semiconductor laser oscillator, the comparison means can be placed close to the light intensity detector, making it less susceptible to noise. .

Furthermore, even if noise occurs in the output of the comparison means,
Light amount control can be performed reliably without being affected by noise.

In the above embodiment, the comparison results are latched twice for each line of beam scanning, and when the two latched comparison results match, the light intensity of the semiconductor laser oscillator is controlled according to the comparison result. The comparison results may be latched two or more times, and in that case, when the plurality of latched comparison results match, the light amount of the semiconductor laser oscillator may be controlled according to the matched comparison result.

[Effects of the Invention] As detailed above, according to the present invention, even high-speed laser printers and high-speed digital copying machines can be used without consuming excess toner. Stable laser oscillator light intensity that is not affected by noise without using a microcomputer, and even if the light intensity detection means that detects the laser oscillator light intensity is far from the laser oscillator light intensity control unit. A control device can be provided.

[Brief explanation of drawings]

The figure is for explaining one embodiment of the present invention.
The figure is a block diagram showing an overview of the light amount control device for a laser oscillator, FIG. 2 is a block diagram showing a part of the light amount control device for the laser oscillator in detail, FIG. 3 is a timing chart explaining the operation, and FIG. It is a flowchart explaining the operation. 9...Polygon mirror 10...Photoreceptor (image carrier),]1...Laser oscillator, 12
... Laser beam, 15 ... Light amount detection means, 16 ... Reference signal generation means, 17 ...
... Comparison means, 18 ... Beam detection means, 1
9... Latch signal generating means, 20...
Latch circuit (holding means), 21... light amount control means, 22... drive means. Figure 4 (B)

Claims (1)

[Claims] Scanning means for scanning a surface to be scanned by scanning a laser beam output from a laser oscillator; driving means for driving the laser oscillator with current; and light amount detection for detecting the amount of light from the laser oscillator. means for comparing the light quantity detection signal of the light quantity detecting means with a preset reference signal; beam detecting means for detecting the position of the laser beam scanned by the scanning means; holding means for holding the comparison results of the comparison means multiple times based on the beam detection signal; and when the plurality of comparison results held by the holding means match, the drive current of the drive means is adjusted according to the comparison result. A light amount control device for a laser oscillator, comprising a light amount control means for controlling the light amount of the laser oscillator by setting.