JPS62235975A - Light quantity control device - Google Patents

Abstract

PURPOSE:To reduce an error at the control of the quantity of a laser beam by changing a laser current by one step and then comparing the quantity of detected light with the delay of a fixed time for converging a transient phenomenon. CONSTITUTION:The quantity of a beam outputted from a laser 1 is detected by a detecting photodiode 8, arithmetically amplified 13 and then A/D converted in a microprocessor MPU14, the digital signal is compared with a reference value selected out of plural reference values stored in a ROM14-2 in accordance with light quantity switching signals S1-S3 and a signal corresponding to the reference value is outputted from the MPU14. The output signal is D/A converted 15 and supplied to a constant current circuit 20 through a current/ voltage converting circuit 18 to control the driving current of the laser 1 through transistors 22, 25, 26, so that quantity of the laser beam is adjusted. If the values of output ports 01-09 of the MPU14 are changed by one bit, the current of the laser 1 is increased like steps, and after the passage of a waiting time for converging the transient variation of driving currents of the converter 15 and amplifiers 19, 21, the quantity of the laser beam is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light amount control device for controlling the amount of light of a light emitting element, particularly a laser such as a semiconductor laser.

[Prior Art] In laser scanning type recording devices, such as laser beam printers and laser copying machines, in which a photosensitive drum is scanned with a laser beam to record text and image information on a recording medium, the photosensitive drum must be replaced. In this case, since there are variations in sensitivity for each photosensitive drum, it is necessary to switch the amount of laser light depending on the sensitivity characteristics.

As a light amount control device for this purpose, for example,
The one disclosed in No. 106259 is known. Conventional devices of this type generally have multiple comparators that compare the laser light intensity detection output with a reference voltage, decode the sensitivity signal taken out from the photosensitive drum unit, and use the comparator output corresponding to the decoded sensitivity to specify the laser light intensity. The amount of laser light is controlled according to this judgment.

Furthermore, when controlling the above-mentioned laser light intensity, a control method is generally used in which the light intensity is set between each page and held for one page. In such a case, a digital hold circuit using a D/A converter is used as a stable hold circuit to maintain a constant amount of light for a relatively long time.

[Problems to be Solved by the Invention] However, in such a conventional light amount control device, when controlling the light amount, the light amount is digitally changed step by step. A transient phenomenon occurred, which caused control errors.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a light amount control device in which transient phenomena when changing the light amount stepwise do not cause errors in light amount control.

[Means for Solving the Problems] In order to achieve the present object, the present invention provides a light amount changing means for changing the amount of light emitted from a light beam emitted from a light emitting element, a light amount detecting means for detecting the amount of emitted light, and a light amount detecting means for detecting the amount of emitted light. a comparison means for comparing the output value of the detection means with a preset reference value; a signal output means for changing the output digital signal according to the comparison result of the comparison means; and a light amount according to the output digital signal from the signal output means. It is characterized by comprising: a light amount control means for controlling the changing means; and a delay means for delaying the time from when the output digital signal is changed by the signal output means until the comparison is performed by the comparison means by a predetermined time. do.

[Function] In the present invention, a light amount changing means changes the amount of light emitted from the light beam emitted from the light emitting element, a light amount detecting means detects the amount of emitted light, and an output value of the light amount detecting means and a preset reference value are provided. a signal output means for changing the output digital signal according to the comparison result of the comparison means, and a light amount $IJ control for controlling the above-mentioned light amount changing means according to the output digital signal from the signal output means. The delay means, such as a timer, delays the time from when the output digital signal is changed by the signal output means until the comparison is performed by the comparison means by a predetermined time.

In this way, after changing the output signal for controlling the light amount, a certain delay time is provided before comparing the light amount with the reference value, which reduces transient phenomena when changing the light amount and improves control. Errors can be reduced.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the basic configuration of an embodiment of the present invention. In this figure, a is a light amount changing means for changing the amount of light emitted from the light beam emitted from the light emitting element, C is a light amount detecting means for detecting the amount of emitted light, and d is an output value of the light amount detecting means C, which is set in advance. Comparing means for comparing with a reference value, e is a signal outputting means for changing the output digital signal according to the comparison result of the comparing means d, and f is a light amount changing means a for changing the output digital signal according to the output digital signal from the signal outputting means e. This is a light amount control means. Denoted at g is a delay means for delaying the time from when the output digital signal is changed by the signal output means e until the comparison is performed by the comparison means d by a predetermined time.

FIG. 2 shows a circuit configuration of an embodiment of the present invention.

In this figure, 1 is a semiconductor laser (hereinafter referred to as a laser) as a laser generating means, and the recorded image signal VID
Generates a laser beam corresponding to EO. 2 is a laser protection diode, 3 is an overshoot prevention resistor, 4, 5.
6 and 7 are capacitors and resistors for correcting frequency characteristics. When the connection line between the laser 1 and the laser drive circuit is long, these capacitors and resistors 4 to 7 are connected to both ends of the line.

Reference numeral 8 denotes a photodiode for detecting the amount of laser light as a light amount detection means for detecting the amount of light generated from the laser 1. Reference numeral 9 indicates a variable resistor for correcting sensitivity variations in the photodiode 8, and reference numeral 10 indicates a load resistance of the photodiode 8. 1
1 and 12 are resistors, 13 is an operational amplifier (op-amp)
It is.

14 is an A/D (analog-to-digital) converter;
RO as a storage means that stores digital reference values (comparison values) according to the characteristics of the D converter 14-1 and the photoreceptor.
It is a one-chip microprocessor with a built-in read-only memory (read-only memory), and includes comparison means and means for performing the comparison operation according to the present invention according to the control procedure shown in FIG. 3, which is stored in advance in an internal program memory (not shown). It has the functions of a signal output means, a light amount control means, and a delay means.

15 is a D/A (digital-to-analog) converter that converts the digital output of the microprocessor 14 into an analog signal. 16 and 17 are mouth/A converters 15
This is a resistor for determining the reference current.

18 is a current-voltage conversion circuit using an operational amplifier 19; 20
is connected to the output side of the current-voltage conversion circuit 18, and is a constant current circuit using an operational amplifier 21 and a transistor 22.

23.24 is a coil and resistor for frequency characteristic improvement, 25.
26 is a transistor constituting a current switch; 27 to 3;
0 is resistance. 31 is a NAND (not product) circuit connected to the base of the transistor 26, 32 is an OR (logical sum) circuit connected to one end of the input terminal of the NAND circuit 31, and these circuits 18 to 32 drive the laser 1. This constitutes a light amount changing means that controls the drive current.

33 to 36 are input terminals of the microprocessor 14;
33 is a terminal to which a light amount control start signal APC5T is applied;
34 to 36 are terminals to which a light amount switching signal 5t-33 is applied. 37 is a terminal to which a scanner ready signal 5CNRDY is applied, which indicates that a motor (not shown) that rotates a rotating polygon mirror (not shown) for laser beam deflection is rotating at a specified speed; Connected to one input end. 38 is a terminal to which the recording image signal VIDEO is applied, and is connected to one input end of the OR circuit 32. Also, the capacitor 3 in the constant current circuit 20
9 prevents waveform overshoot that occurs when the output of the D/A converter 15 changes.

In the above configuration, the light intensity of the laser beam outputted from the laser 1 is detected by the laser light intensity detection photodiode 8, and the detected value of the photodiode 8 is amplified by the operational amplifier 13, and then sent to the A/D in the microprocessor 14. The signal is converted into a digital signal by the converter 14-1. This digital signal is compared with a reference value selected from a plurality of reference values prestored in the ROM 14-2 according to the light amount switching signals 51 to S3, and a digital signal corresponding to this reference value is sent to the microprocessor. It is output from 14.

After the digital signal output from the microprocessor 14 is converted into an analog signal by the D/^ converter 15,
The current is supplied to the constant current circuit 20 through the current-voltage conversion circuit 18, and the driving current of the laser 1 is controlled via the transistors 22, 25, 26, and the amount of laser light is adjusted.

Next, the operation of the one-chip microprocessor 14 shown in FIG. 2 will be explained with reference to the flowchart shown in FIG. 3 and the timing chart shown in FIG.

First, when the light amount control start signal APC5T is applied to the terminal 33, the microprocessor checks whether it is a rising edge portion (steps 100, 101).

In addition, in the diagram of FIG. 3, ■1 to 13. I4 indicates an input port. Further, the above-mentioned signal APC5T is a signal that is output immediately before starting image recording, and is generated between each page when continuous recording is performed. However, it does not have to be every l page.

When the rising edge of the light intensity control start signal APC5T is detected (step 101), the internal timer TMI of the microprocessor 14 is started (step 102), and the output ports -01 to 09 are cleared (step 103), and the output port is cleared. 010 is turned on (step 104).

Since the output port O1O is connected to the input terminal of the OR circuit 32, when the output port 010 is turned on,
If the scanner ready signal 5CNRDY is already in the on state, the current switch constituted by the transistors 25 and 26 operates in the direction of causing the drive current to flow through the laser 1.

Next, light amount switching signals 31 to S3 indicating the sensitivity of the photosensitive drum (not shown) are taken in from the input ports 11 to 3,
Decode (step 105). Next, the data (reference value) recorded in the ROM 14-2 corresponding to the result of this decoding is selected (step 106), and the data that is the selected light amount control reference value is stored in the internal memory M1 (not shown). (Step 107). After processing up to this point, the process returns to the first step 5IOI.

Next, a case where the PC5T does not reach the rising edge of the light amount control start signal will be described. In this case, step 100.1
Since 01 is a negative determination, the process proceeds to step 108, where it is determined whether or not the above-mentioned timer TMI is operating. If not, output port 010 is turned off at step 109, and the process returns to the first step 101. .

If the timer TMI is operating (step 108), the A/D conversion value obtained by converting the analog input capo-ANI data by the A/D converter 14-1 and the data stored in the memory M1 (reference value ), and if the A/D converted value is smaller (step 110). Output boat O1~
1 bit is added to the value of 09 (step 111).

When the values of output ports 01 to 09 change by 1 bit, the output current value of the constant current circuit 20 changes, and as shown in FIG. 4, the current of the laser 1 (laser drive current) increases by one step ( Rise. At this time, a setting time delay of the D/A converter 15, a delay in the rise of the operational amplifiers 19 and 21, an overshoot, etc. may occur.

This is illustrated by the waveform shown at A in FIG. Therefore, a waiting time t1 is provided in order to detect the amount of laser light after the transient fluctuation of the laser drive current has converged (step 112).

Next, it is determined whether or not the timer TMI has reached a predetermined specified time (step 113), and if the specified time has been reached, the timer TMI is stopped (step 114).
, return to the first step 100 again.

On the other hand, when step 110 is affirmative, that is, ^/
The A/D conversion value of the D converter 14-1 is stored in the memory M1.
If the data is larger than the data stored in
If Ih4 has not been completed, the process directly returns to the first step 100.

Output ports 01 to 0 of the microprocessor 14 in FIG.
Although 9 is shown as a 9-bit parallel port, many commercially available microprocessors have an 8-bit parallel port. Therefore, if you output the lower 8 bits of the 9-bit parallel output from one parallel port and the most significant 1 bit from another port, the output will turn off (OFF).
When changing from H to (10G) H, temporarily (I
FF) H, resulting in the inconvenience that an excessive current flows through the laser l. Therefore, when using an 8-bit parallel boat, the top 8
The same effect can be obtained by setting the bits as one parallel port and outputting the lowest 1 bit from another port.Alternatively, in this case, a 9-bit latch circuit (not shown) can be provided at the input port of the D/A converter 15. is obtained.

In the above embodiment, the amount of light is controlled by controlling the driving current of the laser, but the amount of light can also be controlled by passing the laser beam through a filter or the like. This can be achieved by controlling the amount of transmitted light by controlling the voltage value and duty ratio applied to the liquid crystal, or by changing the aperture.

[Effects of the Invention] As explained above, according to the present invention, the laser current is reduced to 1
A certain time t for the transient phenomenon to converge after changing the step
Since the amounts of detected light are compared with a delay of 1, it is possible to significantly reduce errors in controlling the amount of laser light.

[Brief explanation of drawings]

1 is a block diagram showing the basic configuration of an embodiment of the present invention; FIG. 2 is a circuit diagram showing a circuit configuration of an embodiment of the present invention; FIG. 3 is a flowchart showing the operation of the embodiment of FIG. 2; FIG. 5 is a timing chart showing the output timing of the embodiment of FIG. 2, and FIG. 5 is a block diagram showing the configuration of the main part of another embodiment of the present invention. 1...Laser, 2...Photodiode for detecting laser light amount, 13.1
9.21...Operation amplifier, 14...Microprocessor, 14-1...-A/D converter, 14-2...ROM. 15-- Port/A converter, 18-- Current voltage conversion circuit, 20- Constant current circuit. Basic configuration of the example

Claims (1)

[Scope of Claims] 1) a) light amount changing means for changing the amount of light emitted from the light beam irradiated from the light emitting element; b) light amount detecting means for detecting the amount of emitted light; and c) an output of the light amount detecting means. a comparison means for comparing the value with a preset reference value; d) a signal output means for changing the output digital signal according to the comparison result of the comparison means; and e) a signal output means for changing the output digital signal from the signal output means. light amount control means for controlling the light amount changing means accordingly; f) delaying the time from when the output digital signal is changed by the signal output means until the comparison is made by the comparison means by a predetermined time; 1. A light amount control device comprising a delay means.