JPH05131675A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent light emitting elements from being lighted in error, deteriorated, and the like by a method wherein when the light emitting elements are controlled under APC, the APC is worked only when it is required. CONSTITUTION:A title device is provided with a sample hold circuit 14 holding a result in comparing a detection value of the intensity of light from a semiconductor laser 119 that produces a scanning optical beam with a reference value as a sample; a light emitting element drive circuit 120 driving the semiconductor laser 119 in accordance with the voltage held by the sample hold circuit 114; and a reset circuit 113 resetting the voltage held by the sample hold circuit 114.

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 or the like 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 and adversely affecting a formed image due to variations in light emitting elements, thermal characteristics of the light emitting elements, etc. APC (auto power control) is applied so that the same light intensity can always be obtained by feeding back. However, since this APC has a configuration in which the light emitting element is directly modulated, even in the non-image area, AP
It was necessary to do C. For example, in the non-image area between recording materials, or in the non-image area of each row during image formation of the same recording material, the light emitting element is driven to convert the light intensity of the light beam into a voltage, CPU that changes the voltage
(Central processing unit) monitors the light intensity of the light beam to be constant.

[0003]

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

Alternatively, there is a configuration in which the light intensity of the light beam is sampled and held in the non-image area to perform APC without intervention of the CPU, but the capacitor for sample and hold remains charged. , Due to erroneous lighting of the light emitting element due to noise, erroneous lighting of the light emitting element during the unstable voltage period when the power supply rises, etc.
There are problems such as deterioration of the light emitting element, user's clogging of the recording material, and protection of the user when replacing the process cartridge.

An object of the present invention is to provide an image forming apparatus which solves the above problems.

[0006]

In order to achieve the above object, the present invention comprises a sample and hold means for sampling and holding a comparison result between a detected value of light intensity from a light emitting element for generating a scanning light beam and a reference value, The light emitting element driving means drives the light emitting element according to the hold voltage held by the sample hold means, and the reset means resets the voltage held by the sample hold means.

[0007]

According to the present invention, the light emitting element is turned on only for a necessary period and malfunction is prevented.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1, FIG. 2, and FIG. 3 each show a first embodiment of the present invention. FIG. 1 is a block diagram showing an outline of the embodiment apparatus, FIG. 2 shows a detailed concrete example of a sample hold circuit, and FIG. 3 shows timings of the signals of FIGS. ..

In FIG. 1, 101 is a photosensitive drum which is sensitive to a light beam and forms a toner image, 119 is a semiconductor laser, 102 is a polygon mirror which scans the light beam 103 emitted from the semiconductor laser 119, and 118 is a semiconductor. A photodetector as a light intensity detecting means for detecting the light intensity from the laser 119, a photoelectric conversion circuit 117 as a light intensity voltage converting means for converting the light intensity from the photodetector 118 into a voltage, and a predetermined light 116. A reference voltage generating circuit for generating a reference voltage for obtaining strength, 11
Reference numeral 5 is a comparison circuit as a comparison means for comparing the light intensity voltage converted voltage by the photoelectric conversion circuit 117 with the reference voltage of the reference voltage generation circuit 116, and 114 is a sample hold means for holding the comparison result for a predetermined period. It is a sample hold circuit. Reference numeral 121 denotes a semiconductor laser 119 according to the hold voltage of the sample hold circuit 114.
Is a current setting circuit as a driving current setting means for setting the driving current, and 120 is a semiconductor laser driving circuit as a light emitting element driving means for switching the semiconductor laser 119 according to the set driving current. Reference numeral 107 denotes an image signal mask circuit, which sends an image signal input through the CPU 111 to the semiconductor laser drive circuit 120.
The image signal is masked only when an unblank signal (described later) is input.

Reference numeral 108 denotes a beam detector for detecting the scanning position of the light beam emitted from the semiconductor laser 119 and scanned by the polygon mirror 102. Reference numeral 109 denotes a waveform shaping circuit for shaping the detection signal from the beam detector 108. .. Reference numeral 110 is a timing signal for instructing the output timing of the beam detector 108 and the timing for the sample hold circuit 114 to sample and hold the input signal based on the signal from the CPU 111, and the image signal mask circuit 107 masks the image signal in the image area. And a first timing generating circuit as a timing generating means for generating an unblank signal for performing the operation.

Reference numeral 113 is a sample and hold voltage reset circuit for resetting the voltage sampled and held by the sample and hold circuit 114, and 112 is a second timing generation circuit. Reference numerals 103 to 106 represent light beams.

As shown in FIG. 2, the semiconductor laser 119 and the photodetector 118 are contained in the same package. 203 is an operational amplifier, 204 is a comparator,
Reference numeral 205 is an analog switch, 207 is a voltage holding capacitor, 113 is an FET (field effect transistor) that discharges the capacitor 207 according to a reset signal input to the input terminal 213, 209 is an operational amplifier with a large input impedance, 210 Is a Darlington type transistor that constitutes the voltage setting circuit 121. The semiconductor laser drive circuit 120 is composed of a switching circuit.

First, in the non-image area outside the photosensitive drum 101, the input terminal 21 of the semiconductor laser drive circuit 120 is provided.
The semiconductor laser 119 is forcibly turned on in response to an input signal from the optical amplifier 2, and the voltage indicating the light intensity from the photodetector 118 is amplified by the operational amplifier 203 to obtain the converted and amplified voltage indicating the light intensity and a predetermined light intensity. The comparator 204 compares the reference voltage set so as to be set. The comparison result is input to the input terminal 206 by the APC signal for performing the APC control operation, and the analog switch 20
Sample-hold capacitor 20 with 5 turned on
Charge to 7. Operational amplifier 209, transistor 2
10, the APC control operation is performed so that a predetermined light intensity is obtained, and the analog switch 205 is turned off during image formation to control the current by the operational amplifier 209 and the transistor 210 based on the voltage of the hold capacitor 207. To do.

FIG. 3 shows A in the last line of the image forming member.
The timing of PC and sample hold reset is shown. In FIG. 3, 301 is a position detection signal (BD signal) of the light beam output from the beam detector 108 of FIG. 1, 303 is an APC signal indicating the timing of forced lighting and sample hold of the laser, and 304 is the sample of FIG. A voltage waveform charged in the hold capacitor 207, 305 is an image signal for forming a toner image by irradiating the drum 101, which is an image carrier, with the light beams 104 and 105. Reference numeral 302 denotes an unblanking signal for masking the image signal in the non-image area, and 306 denotes a sample hold reset signal for discharging the voltage 304 charged in the sample hold capacitor 207.

As shown in FIG. 3, in the last row of the image forming member, the first timing generating circuit 110 has the periods 307-.
The APC signal is output to the input terminal 206 of the analog switch 205 by 309 (T _{1 to} T ₃ ). This is 30 of the unblanking signal 302 indicating the non-image area.
It is performed within a period of 7 to 310 (T _{1 to} T ₄ ). The hold voltage of 304 is already charged to the capacitor before performing the sample hold at 307 (T ₁ ). This is because the voltage charged when the sample is held in the previous row is not discharged. Is. In the last line, finish recording for the specified image forming member,
Next, when there is no request for image formation, the second timing generation circuit 112 resets the sample and hold reset circuit 306 in the period 313 to 314 (T _{7 to} T ₈ ).
3 to the input terminal 213 to discharge the voltage of the hold capacitor 304.

FIG. 4 shows a sample hold reset signal when the power is turned on and when the power is turned off. 401
Is the output voltage of the power supply shown as V _CC1 in FIG.
2 is the output voltage of the power supply shown by -V _CC2 in FIG. The power is turned on at 404, and the power is turned off at 410. Since the power supply voltage is unstable when the power is turned on or off, the laser 119 may malfunction. Therefore, when the power supply is turned on and when the image is not being formed, sample hold reset is performed as needed to prevent the laser 119 from malfunctioning when the power supply voltage is unstable.

As described above, in the present embodiment, in the image forming apparatus for forming an image by scanning the light beam from the light emitting element, a sample which requires a low cost to set the light intensity of the light beam to a predetermined value. When performing APC of the light emitting element by the hold method, a means for resetting the sample hold is provided, and by shifting the timing of performing the APC from the timing of performing the sample hold reset, the APC of the light emitting element having high reliability can be obtained at low cost. Can work.

(Other Embodiments) In the first embodiment, the sample hold reset is performed in the last row of the image forming member, but in the second embodiment, the hold voltage is monitored,
A configuration for performing sample hold reset even in the case of an abnormality is shown.

5 and 6 show the second embodiment.

In FIG. 6, in addition to the circuit configuration of FIG. 2 of the first embodiment, a comparator 601 having a high input impedance, and voltage dividing resistors 602 and 603 representing an abnormal voltage are provided.

In FIG. 6, the comparator 601 constantly compares the voltage of the sample and hold capacitor 207 with a predetermined voltage obtained by the voltage dividing resistors 602 and 603, which are considered to be abnormal voltages. A signal is output to the terminal 604.

In FIG. 5, reference numeral 501 is a light beam position detection signal (BD signal), 503 is an APC signal indicating the timing of forced lighting of the laser and sample hold.
Reference numeral 4 is a voltage waveform charged in the sample hold capacitor, 505 is an image signal, and 515 is a detection signal of an abnormal voltage of the hold voltage. 502 is an unblanking signal for masking the image signal in the non-image area, and 50
Reference numeral 6 denotes a sample hold reset signal.

When the sample-and-hold capacitor is charged with an abnormal voltage due to noise or the like as represented by 504 in FIG. 5, a signal 515 is output from the comparator 601 via the terminal of 604, and this is received. The second timing generation circuit 112 outputs the sample hold reset signal at the timing of 506, and 504
The voltage of the hold capacitor indicated by is discharged and sample-hold is performed according to the next APC signal.

As described above, in the second embodiment, the configuration is such that the voltage of the sample-hold capacitor is constantly monitored, so that it is possible to prevent abnormal current from flowing into the light emitting element and causing deterioration or destruction.

[0025]

As described above, according to the present invention,
Problems such as erroneous lighting of the light emitting element, deterioration of the light emitting element, and protection of the user can be solved at low cost and with high reliability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an APC control circuit in an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a circuit configuration of a sample hold circuit of FIG.

FIG. 3 is a timing chart of APC and sample hold reset in the first circuit.

FIG. 4 is a timing chart showing the relationship between sample hold reset and power supply voltage in the circuit of FIG.

5 is a timing chart of APC and sample hold reset in the circuit of FIG.

FIG. 6 is a circuit diagram showing an APC control circuit according to a second embodiment of the present invention.

[Explanation of symbols]

 101 Photosensitive Drum 102 Polygon Mirror 110 First Timing Generation Circuit 112 Second Timing Generation Circuit 113 Sample Hold Reset Circuit 114 Sample Hold Circuit 118 Photodetector 119 Semiconductor Laser

 ─────────────────────────────────────────────────── (72) Inventor Hiroshi Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Junichi Kimizuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (2)

[Claims] 1. A sample-hold means for sample-holding a comparison result between a detected value of light intensity from a light-emitting element for generating a scanning light beam and a reference value, and a hold voltage held by the sample-hold means. An image forming apparatus comprising: a light emitting element driving unit that drives the light emitting element; and a reset unit that resets the voltage held by the sample hold unit. 2. The image forming apparatus according to claim 1, wherein the sample hold period by the sample hold means and the reset period by the reset means do not overlap with each other.