JP2968056B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by scanning a light beam, and is particularly applied to a laser beam printer, a copying machine, etc. having a light intensity control function.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus, in order to prevent the intensity of a light beam from deviating from a set value due to variations in light emitting elements, thermal characteristics of the light emitting elements, and the like, an image is adversely affected. APC (auto power control) is applied so that the same light intensity is always obtained by feedback. However, since this APC is configured to directly modulate a light emitting element, it is necessary to perform APC in a non-image area. For example, in the non-image region between the recording material and the recording material, or in the non-image formation region of each row during image formation of the same recording material, drive the light emitting element to convert the light intensity of the light beam into a voltage, Convert the converted voltage to CPU
(Central processing unit) to make the light intensity of the light beam constant.

[0003]

However, in the above-mentioned conventional example, since the APC of the light emitting element is performed using the CPU, there is a disadvantage that it is expensive.

Alternatively, there has been a configuration in which the light intensity of the light beam is sampled and held in a non-image area without using a CPU, and APC is performed. Since it must be used, there is a disadvantage that the battery is discharged during the hold time. Further, as the speed of the apparatus has been increased and the definition has been advanced, there has been a disadvantage that the capacitor cannot be sufficiently charged in the non-image area.

An object of the present invention is to provide an image forming apparatus capable of realizing APC of a light emitting element at low cost and capable of coping with high-speed recording and high definition in view of the above points.

[0006]

In order to achieve the above object, the present invention is directed to an image forming apparatus for performing an image forming apparatus by scanning a light beam from a light emitting element and detecting the light intensity from the light emitting element. Light intensity detection means, light intensity voltage conversion means for converting the light intensity detected by the light intensity detection means into a voltage, comparison means for comparing the voltage converted by the light intensity voltage conversion means with a reference voltage, Sample and hold means for holding the converted voltage for a predetermined period in accordance with the comparison result of the comparison means, timing generation means for generating a timing for performing sample and hold by the sample and hold means, and a signal held by the sample and hold means Driving current setting means for setting a driving current of the light emitting element according to a hold voltage; and a driving current set by the driving current setting means. Light-emitting element driving means for driving the light-emitting element, wherein the timing generating means variably sets the timing for performing sample-hold by the sample-hold means and the sampling time according to the time from the previous sample-hold timing. It is characterized by doing.

In a preferred aspect of the present invention, the timing generation means variably sets a sampling hold time and a sampling time according to the hold voltage, instead of the time from the previous sample hold timing. Characterized by

[0008]

According to the present invention, the light intensity from the light emitting element is detected by the light intensity detecting means, the detected light intensity is converted into a voltage by the light intensity voltage converting means, and the converted voltage, the held voltage and the reference voltage are converted. The converted voltage is compared by the comparing means, and the converted voltage is held for a predetermined period by the sample and hold means according to the comparison result, and the drive current of the light emitting element is set by the drive current setting means according to the held voltage. Then, the light emitting element is driven by the light emitting element driving means according to the set driving current.

According to the present invention, the timing generating means changes the timing and the sampling time for performing the sample and hold by the sample and hold means according to the hold voltage or the time from the previous sample and hold timing. Since the control is performed, the APC of the light emitting element can cope with high speed recording and high definition at low cost.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1, 2, 3 and 4 show a first embodiment of the present invention. FIG. 1 shows a schematic circuit configuration of the device of the embodiment, FIG. 2 shows a detailed concrete example of the sample and hold circuit of FIG. 1, and FIGS. 3 and 4 show timings of the signals of FIG.

In FIG. 1, reference numeral 101 denotes a photosensitive drum that is sensitive to a light beam and forms a toner image, 102 denotes a polygon mirror that scans a light beam emitted from a semiconductor laser, and 103 denotes a semiconductor laser as a light emitting element. . 1
Reference numeral 04 denotes a photodiode as light intensity detection means for detecting the light intensity from the semiconductor laser 103; 105, a photoelectric conversion circuit as light intensity voltage conversion means for converting the light intensity from the photodiode 104 into a voltage; A reference voltage generating circuit for generating a reference voltage for obtaining light intensity,
Reference numeral 108 denotes a comparison circuit as comparison means for comparing the voltage obtained by the light intensity voltage conversion by the photoelectric conversion circuit 105 with the reference voltage of the reference voltage generation circuit 107, and reference numeral 106 denotes a sample and hold means for holding the comparison result for a predetermined period. Is a sample and hold circuit. Reference numeral 109 denotes the semiconductor laser 1 according to the hold voltage of the sample hold circuit 106.
Reference numeral 03 denotes a current setting circuit as drive current setting means for setting a drive current, and reference numeral 110 denotes a semiconductor laser drive circuit as light emitting element drive means for switching the semiconductor laser 103 in accordance with the set drive current.

Reference numeral 114 denotes a beam detector for detecting the scanning position of the light beam emitted from the semiconductor laser 103 and scanned by the polygon mirror 102; and 113, a waveform shaping circuit for shaping the detection signal from the beam detector 114. Reference numeral 112 denotes a first timing generator as a timing generator for generating a timing signal for instructing a timing for sampling and holding based on the output timing of the beam detector 114 and an unblanking signal for masking an image signal in a non-image area. Circuit. The first timing generation circuit 112 controls the output timing of the image signal generation circuit 111 based on the timing signal from the second timing generation circuit 119.
The image forming signal output from the circuit 111 is sent to the semiconductor laser drive circuit 110. 115 to 118 represent light beams.

In FIG. 2, the semiconductor laser 103 and the photodetector 104 are housed in the same package. 403 is an operational amplifier, 412 is a comparator, 40
4 is an analog switch, 406 is a capacitor for holding a voltage, 408 is an operational amplifier having a large input impedance, and 409 is a Darlington transistor constituting the voltage setting circuit 109. Semiconductor laser drive circuit 11
0 comprises a switching circuit.

First, in the non-image area outside the photosensitive drum 101, the semiconductor laser 103 is forcibly turned on from the input terminal 411, and the voltage indicating the light intensity from the photodetector 104 is amplified by the operational amplifier (operational amplifier) 403 and converted. A voltage indicating the amplified light intensity and a reference voltage set so as to obtain a predetermined light intensity are compared with a comparator 41.
Compare with 2. The comparison result is stored in the analog switch 404.
Is charged to the hold capacitor 406 in the ON state. In the operational amplifier 408 and the transistor 409,
The control operation of the APC is performed until a predetermined light intensity is obtained. During image formation, the analog switch 404 is turned off.
The current is set by the operational amplifier 408 and the transistor 409 based on the held capacitor voltage as the FF.

FIGS. 3 and 4 show timings for performing APC between rows. FIG. 3 shows the timing of APC in the first row, and FIG. 4 shows the timing of APC in the second and subsequent rows.

In FIG. 3, reference numeral 301 denotes a position detection signal (B) of the light beam output from the beam detector 114 of FIG.
D signal), 302 is an unblanking signal indicating a non-image area, 303 is an APC signal indicating timing for forcibly lighting the laser 103 and performing sample and hold, 304 is a voltage waveform of the hold capacitor 406 in FIG. 2, and 305 is an image forming medium. Is an image signal to be recorded on the drum 101. Reference numerals 308 to 312 denote unblanking signals for masking an image signal in a non-image area.
Reference numerals 307 and 308 to 311 denote H (high) level periods of the APC signal. At this time, the semiconductor laser 103 is forcibly turned on and the capacitor 406 of the sample hold is charged. Reference numerals 310 to 311 denote H-level periods of the light beam position detection signal. Reference numeral 313 denotes the rising timing of the image signal.

In FIG. 4, reference numeral 201 denotes a position detection signal (BD signal) of the light beam output from the beam detector 114 in FIG. 1, 202 denotes an unblanking signal indicating a non-image area, and 203 denotes forced lighting of the laser 103 and sampling. APC signal 204 indicating the timing of holding, 204
Is the voltage waveform of the hold capacitor 406 in FIG.
Is an image signal to be recorded on the drum 101 as an image forming medium. Reference numerals 207 to 210 denote unblanking signals for masking an image signal in a non-image area;
Reference numeral 209 denotes an H level period of the APC signal. At this time, the capacitor 406 for forced lighting of the semiconductor laser 103 and the sample and hold is charged. Reference numerals 208 to 209 denote H-level periods of the light beam position detection signal. Reference numeral 212 denotes a rising timing of the image signal.

In the APC at the time of the first row in FIG.
The timing generation circuit 112 outputs the APC signal to the terminal 405 of the sample-and-hold circuit 106 in two periods, namely, periods 306 to 307 and periods 308 to 311. This is because the charge is not charged in the hold capacitor 406 in the APC in the first row,
Since the charging takes time, the APC is performed twice in order to sufficiently charge the battery. On the other hand, in the APC in the second and subsequent rows in FIG.
The charge can be sufficiently performed in a shorter time than the APC of the first row in the periods 207 to 209. 207-209 and 3
The APC timings 08 to 311 are set from the first timing generation circuit 112 in FIG. 1, and the APC timings 306 to 307 are set from the second timing generation circuit 119 in FIG.

As described above, in this embodiment, in an image forming apparatus for forming an image by scanning a light beam from a light emitting element, a low-cost sample for setting the light intensity of the light beam to a predetermined value can be obtained. When the APC is performed between rows by the hold method, the time of the APC in the first row is set to the AP from the second row.
Since the setting is made longer than the C time, even if a capacitor having a large capacity capable of preventing discharge during the hold time is used, the capacitor for the sample hold can be sufficiently charged.

(Other Embodiments) FIGS. 5 and 6 show a second embodiment of the present invention.

In the first embodiment, the start timing of the APC in the first row is set to a predetermined time, but in the second embodiment, the sample-hold capacitor is charged in the first row. When the voltage is below a certain level, the APC time is extended.

In FIG. 5, reference numerals 501 to 518 denote parts 1 in FIG.
01 to 118. A second timing generation circuit 519 detects the voltage of the capacitor (606 in FIG. 6) of the sample and hold circuit 506, and if it is lower than a predetermined value, sets the APC start time earlier to start.

FIG. 6 corresponds to FIG.
09, 611, and 612 are 403 to 409 and 41 in FIG.
1, 412. Reference numeral 613 denotes a comparator having a high input impedance.
6 is compared with a predetermined voltage.
The output terminal 614 of the comparator 613 is connected to the second timing generation circuit 519. Here, the predetermined voltage is a voltage that can be sufficiently charged during the period of APC time 207 to 209 in FIG.

As described above, in the first embodiment, the APC time is always set longer for the first row, whereas in the second embodiment, the APC time is increased only when necessary. Since the configuration is employed, APC can be completed in a short time when an image is continuously formed, thereby providing an advantage that deterioration of the semiconductor laser can be prevented.

[0026]

As described above, according to the present invention,
In an image forming apparatus that forms an image by scanning a light beam from a light emitting element, when performing APC by a sample hold method for setting the light intensity of the light beam to a predetermined value,
For example, the APC time of the first row is set longer than the APC time from the second row, or the APC time is lengthened when the voltage charged in the sample-hold capacitor in the first row is lower than a certain level. As a result, even if a capacitor having a large capacity capable of preventing discharge during the hold time is used, the effect of sufficiently charging the capacitor for sample hold can be obtained, whereby the APC of the light emitting element can be realized at low cost, and An effect capable of coping with high-speed recording and high definition is obtained.

[Brief description of the drawings]

FIG. 1 illustrates an image forming apparatus according to a first embodiment of the present invention.
FIG. 3 is a block diagram illustrating a circuit configuration of a PC control circuit.

FIG. 2 is a circuit diagram showing a circuit configuration example of a sample-hold circuit of FIG. 1;

FIG. 3 is a timing chart showing APC timing at the time of a first row in the circuit of FIG. 1;

FIG. 4 is a timing chart showing the timing of APC on the second and subsequent rows in the circuit of FIG. 1;

FIG. 5 is a block diagram illustrating a circuit configuration of an APC control circuit according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram showing a circuit configuration example of the sample and hold circuit of FIG. 5;

[Explanation of symbols]

 101, 501 Photosensitive drum 103, 503 Anticonductor laser 104, 504 Photodetector 105, 505 Photoelectric conversion circuit 106, 506 Sample hold circuit 107, 507 Reference voltage generation circuit 108, 508 Comparison circuit 109, 509 Voltage setting circuit 110, 510 Semiconductor laser Drive circuit 112, 512 First timing generation circuit 114, 514 BD sensor 119, 519 Second timing generation circuit 404, 604 Analog switch 406, 606 Capacitor for sample hold

──────────────────────────────────────────────────続 き Continuing on the front page (72) Takashi Seiya, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Junichi Kimizuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-63-86585 (JP, A) JP-A-62-154964 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/44 G03G 15/04

Claims (2)

(57) [Claims] 1. An image forming apparatus for performing an image forming apparatus by scanning a light beam from a light emitting element, wherein the light intensity detecting means detects light intensity from the light emitting element, and the light detected by the light intensity detecting means. Light intensity voltage converting means for converting the intensity into a voltage, comparing means for comparing the voltage converted by the light intensity voltage converting means with a reference voltage, and converting the converted voltage according to a comparison result of the comparing means. Sample and hold means for holding for a predetermined period, timing generation means for generating timing for performing sample and hold by the sample and hold means, and drive for setting a drive current for the light emitting element according to the hold voltage held by the sample and hold means A current setting unit; and a light emitting element driving unit that drives the light emitting element according to the driving current set by the driving current setting unit. The image forming apparatus according to claim 1, wherein the timing generating means changes the timing for performing the sample and hold by the sample and hold means and the sampling time in accordance with the time from the previous sample and hold timing. 2. The apparatus according to claim 1, wherein said timing generating means changes a sampling hold time and a sampling time according to said hold voltage, instead of a time from said previous sample hold timing. 2. The image forming apparatus according to 1.