JPH0767820B2 - Laser light quantity control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light amount control device for controlling the laser light amount of an image forming apparatus that irradiates a recording medium such as a photoconductor with a laser beam to form a latent image. It is a thing.

[Conventional technology]

Conventionally, Japanese Patent Application Laid-Open No. 56-106259 has been proposed as an apparatus of this type.

In a device that scans a photosensitive drum with a laser beam to form a latent image, when replacing the photosensitive drum, the amount of laser light is switched according to variations in drum sensitivity, and adjustment is performed so that an image with a constant density is always obtained. There is a need.

Therefore, conventionally, a plurality of comparators that compare the output that detects the laser light amount with the reference voltage are provided, the sensitivity signal extracted from the drum unit is decoded, and the laser light amount is adjusted to the specified value by using the comparator output corresponding to the sensitivity. The amount of laser light was controlled by judging whether or not the laser light was emitted.

[Problems to be solved by the invention]

However, when a plurality of reference voltages are provided, the reference voltage is likely to change due to variations in the voltage dividing resistors for generating the reference voltage and changes in the input current of the comparator, which causes an error in the laser light amount. . Further, since the reference voltage is determined by the value of the voltage dividing resistor, there is a problem that the reference value cannot be freely selected. Further, there are many problems such that it takes time and effort to adjust the voltage dividing resistor.

The present invention has been made to solve the above problems, and the reference value can be freely set without adjusting the voltage dividing resistance, and the laser light amount can be set according to the ratio manually set when the drum is replaced, for example. It is an object of the present invention to obtain a laser light amount control device capable of changing

[Means for solving problems]

A laser light amount control device according to the present invention converts an analog signal output from a light amount detection means into a digital signal.
A / D conversion means, reference value data storage means for storing reference value data corresponding to the light amount level of the laser, and reference value data selected from the reference values stored in the reference value data storage means Variable means for varying in proportion, comparing means for comparing the reference value data selected or the reference value data varied by the varying means with the value converted by the A / D converting means, and the output of this comparing means into an analog signal. D / A to convert
The conversion means and the current control means for controlling the current applied to the laser according to the output of the D / A conversion means are provided.

[Action]

In the present invention, when the light amount detecting means detects the light emission of the laser, the output of the light amount detecting means is converted into a digital signal by the A / D converting means, which is selected in advance according to the converted digital signal and the light amount level of the laser. The comparison means compares the stored reference value data or the reference value data changed by the changing means. Based on the output of the comparison means, the current control means controls the current applied to the laser.

〔Example〕

FIG. 1 is a block diagram for explaining the configuration of a laser light amount control device showing an embodiment of the present invention, in which 1 is a semiconductor laser and 2 is a diode for protecting the semiconductor laser 1. Three
Is a resistor that prevents overshoot of the current flowing through the semiconductor laser 1. 4,5 are capacitors, 6 and 7 are resistors, and 4 to 7 are provided at both ends when the wiring cable between the semiconductor laser 1 and the drive circuit is long to correct the frequency characteristic. A photodiode 8 detects the laser light amount. Reference numeral 9 is a variable resistor that corrects the sensitivity variation of the photodiode 8. A load resistor 10 is connected to the variable resistor 9. Reference numerals 11 and 12 are resistors that determine the gain of the operational amplifier 13. 14 is a one-chip microcomputer (hereinafter referred to as a microcomputer), which is an analog multiplexer (MPX) 14a, A / D
It has a converter 14b, a ROM 14c, and the like. The ROM 14c stores reference data (digital value) corresponding to the light intensity level, which will be described later, and the microcomputer according to the input light intensity level.
14 selects arbitrary reference value data. 15 is a D / A converter (D
/ A), the digital signals output from the ports 01 to 09 of the microcomputer 14 are received by the ports A1 to A9, converted into analog signals, and output from the port I _OUT to the current-voltage conversion circuit 16.
The current-voltage conversion circuit 16 is composed of an operational amplifier 17 and the like. The reference potential of the D / A converter 15 is determined by the resistors 18 and 19. Further, V _{(+ R)} and V _(-R) indicate reference current values of the D / A converter 15. 20 is a constant current circuit, operational amplifier 21, transistor 2
The capacitor 23 is composed of two capacitors 23, and the capacitor 23 prevents overshoot that occurs when the output of the D / A converter 15 is converted. 24 is a resistor, 25 is a coil, and the frequency characteristics are improved by the coil 25 and the resistor 24. A current switch 26 is composed of transistors 27 and 28 and resistors 29 to 32. 3
An OR gate 3 ORs a signal output from the port 010 of the microcomputer 14 and an image signal VDO (transmitted from the host side (not shown)). Reference numeral 34 is a NAND gate, which takes the NAND of the output of the OR gate 33 and the scan ready signal SCNRDY. The output of the NAND gate 34 is output to the base of the transistor 27 of the current switch 26. Reference numeral 35 denotes a terminal to which the light amount control start signal APCST is applied and is input to the input port I4 of the microcomputer 14. Reference numerals 36 to 38 denote terminals to which the light amount switching signals S1 to S3 are applied and input to the input ports I1 to I3 of the microcomputer 14. 39
Is a changeover switch, and when this changeover switch 39 is on, the automatic mode for automatically determining the light amount setting value is set,
When it is off, the manual mode is set to change the light intensity setting value manually. Reference numeral 40 denotes a variable resistor which constitutes the variable means of the present invention, and when the changeover switch 39 is off, the analog input AN1 which is a manual reference value is inputted to the internal memory of the microcomputer 14. The output of the operational amplifier 13 becomes the unlogged input AN2 of the microcomputer 14. The scan ready signal SCNRDY is a signal indicating that a motor for driving a rotary polygon mirror (not shown) for deflecting a laser beam is rotating at a specified speed. In addition, the light intensity control start signal APCST
Is a signal output from the control means of the printer (not shown) prior to the start of image recording. The microcomputer 14 also serves as the comparison means of the present invention.

Next, the laser light amount control operation according to the present invention will be described with reference to FIG.

FIG. 2 is a flow chart for explaining an example of the laser light amount control operation according to the present invention. Note that (1) to (17) indicate each step.

First, it is determined whether or not the light amount control start signal APCST is applied to the terminal 35 and is input to the input port I4 of the microcomputer 14 (1). If NO, the process proceeds to step (11) and thereafter, and if YES, to the input port I4. It is determined whether or not the rising of the input light amount control start signal APCST is detected (2). If NO, the process proceeds to step (11) and thereafter, and if YES, the internal timer of the microcomputer 14 is started (3), and 14
Clear ports 01-09 (4). As a result, D / A
The port I _OUT of the converter 15 becomes “0”, and the current flowing through the transistor 22 of the constant current circuit 20 also becomes “0”. Therefore,
No current is applied to the semiconductor laser 1 even if the transistor 28 of the current switch 26 is turned on. Next, the port 010 of the microcomputer 14 is set to HIGH (content "1") (5). Then, the microcomputer 14 determines whether the changeover switch 39 is in the ON state, that is, whether the automatic mode is requested.
Judging from the contents of the input port I5 of (6), if NO, the A / D converter 14b A / D-converts the unlogged input AN2 (7) and the A / D-converted value in the internal memory of the microcomputer 14 (reference value Data) and then proceed to step (10) and thereafter. . At that time, when A / D conversion of the analog input AN2 is performed, data is read multiple times in consideration of the conversion error and noise superimposed on the analog signal, and the average value thereof is set as the true data. It is processing.

On the other hand, if the result of the determination in step (6) is YES, the mode for controlling the light amount is based on the data stored in the ROM 14c, and the light amount switching signals S1 to S3 input to the terminals 36 to 38 are input ports I1 to I3. To receive. Then, this light quantity switching signal S1
S3 are decoded (8), reference data corresponding to the designated light amount level is selected from the ROM 14c (9), and the selected reference value data is stored in the internal memory (10).

On the other hand, if NO in the judgment of step (2), the microcomputer
Determine whether 14 timers (not shown) are running (1
1) If NO, set port 010 of microcomputer 14 to LOW (12) and end control. This allows the current switch 26
Transistor 28 is turned off and the current of the semiconductor laser 1 is cut off.

On the other hand, if NO in the judgment in step (11), analog input
Judge whether the reference data (M1 data) stored in the internal memory is larger than the A / D converted value obtained by A / D converting AN1 (13). If YES, proceed to step (16) and thereafter. YES
If this is the case, the value output from ports 01 to 09 is added by "1" (14). As a result, the current of the semiconductor laser 1 increases by 1 bit of the D / A converter 15 (15). Next, the microcomputer
When the ports 01 to 09 of 14 are changed, the laser current increases and a predetermined delay correction time (t ₁ ) until the laser current is transmitted to the analog input AN1 of the microcomputer 14, that is, the step (1
It is judged whether the timer started in 1) has timed out (16). If NO, the control is ended, and if YES, the timer is stopped (17) and the control is ended.

In the above embodiment, the case where the time for adjusting the light quantity is controlled by the timer has been described, but instead of the timer, the RAM of the microcomputer 14 may be provided with an area for storing whether or not the light quantity is being adjusted for the control. Further, the adjustment ratio may be finely adjusted by providing a plurality of variable resistors 40. Further, the variable resistor 40 is not limited to being variable and may be a fixed resistor.

Next, the laser light amount readjustment operation according to the present invention will be described with reference to FIG.

FIG. 3 is a flow chart for explaining the laser light amount readjustment operation according to the present invention. In addition, (21) ~ (23)
Indicates each step. Further, when the operation is the same as the flow of FIG. 2, the same step number is added and the description is omitted.

When the photosensitive drum is replaced, it is necessary to readjust the laser light amount manually set before the replacement. Therefore, if NO is determined in step (6), steps (8) and (9) are performed. Next, it is judged again from the contents of the input port I5 of the microcomputer 14 whether the changeover switch 39 is in the ON state, that is, whether the automatic mode is requested (21), and if YES, the process returns to step (10), NO
If so, the value converted in step (7) is normalized with the median value of the variable resistor 40 set to "1" (22). Then, the normalized value is multiplied by the reference data selected in step (9) (23), and the multiplication result, that is, the rate (%) of changing the light amount is stored in the internal memory of the microcomputer 14 (10). . This makes it possible to change the amount of laser light at a rate manually set when the photosensitive drum is replaced.

〔The invention's effect〕

As described above, the present invention includes A / D conversion means for converting the unlogged signal output from the light quantity detection means into a digital signal, and reference value data storage means for storing reference value data corresponding to the light quantity level of the laser. Variable means for varying selected reference value data among the reference values stored in the reference value data storage means at a predetermined ratio, and selected reference value data or reference value data varied by the variable means.
Comparison means for comparing the value converted by the A / D conversion means, D / A conversion means for converting the output of the comparison means into an analog signal, and applying to the laser according to the output of the D / A conversion means Since the current control means for controlling the current is provided, it is not necessary to adjust the variation of the voltage dividing resistor, and the reference value can be freely set without being influenced by the value of the voltage dividing resistor. Moreover, since the rate of change of the set reference value can be specified manually, for example, when exchanging the photosensitive drum, the laser light amount can be changed at the rate set manually, which is an excellent advantage that allows user-specific density setting. Have.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the configuration of a laser light amount control device showing an embodiment of the present invention, and FIG. 2 is a flow chart for explaining an example of a laser light amount control operation according to the present invention.
FIG. 3 is a flow chart for explaining the laser light amount readjustment operation according to the present invention. In the figure, 1 is a semiconductor laser, 2 is a diode, 14 is a microcomputer, 14a is an analog multiplexer, 14b is an A / D converter, 14c is a ROM, 15 is a D / A converter, 20 is a constant current circuit, and 26 is a current switch. , 39 is a changeover switch, and 40 is a variable resistor.

Claims (1)

[Claims] 1. A laser light quantity control device for controlling a laser light quantity according to a light quantity signal outputted from a light quantity detecting means for detecting a laser light quantity, wherein an analog signal outputted from said light quantity detecting means is converted into a digital signal. A / D
Conversion means, reference value data storage means for storing reference value data corresponding to the light amount level of the laser, and selected reference value data among the reference values stored in the reference value data storage means at a predetermined ratio. Variable means for varying, comparing means for comparing the selected reference value data or the reference value data varied by the varying means with the value converted by the A / D converting means, and converting the output of this comparing means into an analog signal. Do
A laser light amount control device comprising: a D / A conversion means; and a current control means for controlling a current applied to the laser according to an output of the D / A conversion means.