JP2000127494A - Beam-detecting apparatus and laser printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a main scan speed high by stopping an output of a scan beam and also transmitting a driving signal to a semiconductor switch connected in parallel to a resistance load from an external control apparatus when the scan beam enters a light-detecting means, and discharging charges of a semiconductor light-receiving element. SOLUTION: A command for irradiating a laser light from a plurality of laser light-emitting elements is sent from an external control circuit 404 to a laser-driving circuit 403 in response to a timing detection signal 405 irradiated to a BD sensor 306. Lasers 401 and 402 start to irradiate light thereby forming images. At this time, the external control circuit 404 which receives the output signal of the BD sensor 306 detecting the laser light controls to stop the irradiation by the laser 401 and to start the irradiation by the laser 402. After the irradiation by the laser is stopped, the control circuit transmits a driving signal to an FET 702 connected in parallel to a resistance load 602 in the BD sensor 306 thereby discharging charges of a photodiode 601 in the BD sensor 306.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning beam detecting device used for a laser printer and a laser printer.

[0002]

2. Description of the Related Art In recent years, laser printers have been technically and economically developed for high speed, high resolution, low cost, and the like. This laser printer includes a laser diode as a light source, and scans in a main scanning direction with a polygon mirror using a light amount corresponding to an image signal as a light source to expose a photosensitive drum. The exposed photosensitive drum rotates in the sub-scanning direction, is developed with toner, is transferred and fixed on a transfer-receiving paper, and is output.

Conventionally, in an image forming apparatus at the time of exposure irradiation to a photosensitive drum, a semiconductor light receiving element is used at a position immediately before a start point of a photosensitive body is detected as a synchronization reference in a main scanning direction at the time of image formation. Beam detecting means. On the other hand, in response to the recent increase in the speed of image output, an image forming method of simultaneously scanning a plurality of lasers in an image forming apparatus has been considered. The multiple scanning beams are:
There is some deviation in the main scanning direction, and the method is used in which the beam output is stopped immediately after the scanning beam enters the light detecting means, and the next scanning beam is detected by the same light detecting means. Can be

[0004]

When the main scanning speed is increased in the above-mentioned beam detecting means, the time required for a plurality of scanning beams to reach the beam detecting means becomes very short. However, in the conventional light detecting means, the charge charged by the semiconductor light receiving element receiving light changes according to the time constant of the resistance connected to the element, so that the next scanning beam Change due to the change cannot be detected.

Therefore, in the present invention, the above-mentioned impossibility is made possible by rapidly increasing the main scanning speed in the image forming apparatus by quickly discharging the charge charged in the light receiving element.

[0006]

According to the first aspect of the present invention,
In the beam detecting device according to the present invention, after the scanning beam enters the light detecting device, the scanning beam generating device stops outputting the beam, and the detection signal is transmitted to the external control device. The external control device transmits a drive signal to a semiconductor switch connected in parallel with the resistive load connected to the light detection means, and forcibly discharges the charge charged in the semiconductor light receiving element. And

According to a second aspect of the present invention, in the beam detecting device according to the present invention, the scanning beam generating means stops outputting the beam after the scanning beam is incident on the light detecting means, and the external control device On the other hand, the detection signal is transmitted,
When the one-shot multivibrator becomes active a predetermined time after this signal becomes active, the semiconductor switch connected in parallel with the resistive load connected to the light detecting means is driven, and the electric charge charged in the semiconductor light receiving element Is forcibly discharged.

According to the third aspect of the present invention, in the beam detecting device according to the present invention, the scanning beam generating means stops outputting the beam after the scanning beam is incident on the light detecting means, and the external control device On the other hand, the detection signal is transmitted,
A predetermined time after this signal becomes active, the Schmitt trigger circuit becomes active, thereby driving the semiconductor switch connected in parallel with the resistive load connected to the light detecting means, and discharging the electric charge charged in the semiconductor light receiving element. The battery is forcibly discharged.

According to a fourth aspect of the present invention, a laser printer according to the present invention is a laser printer including a printer controller and a printer engine, wherein laser beams from a plurality of laser beam generating means are provided in the printer engine. Light detecting means for converting to, a resistive load connected to the light detecting means, a semiconductor switch connected in parallel to the resistive load, a comparing means for comparing the terminal voltage of the resistive load and a predetermined voltage, A signal line for triggering the semiconductor switch, wherein after the scanning beam is incident on the light detecting means, the laser beam generating means stops outputting the beam, and the output of the comparing means becomes active. After a time, the semiconductor switch is activated from the signal line to reduce the resistance load. Characterized in that it acts to reduce the child voltage.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a block diagram of a printer system including a printer controller and a printer engine according to a first embodiment of the present invention. In the figure, 101 is a display, 102
Is a host computer. A printer controller 103 converts image data transmitted from the computer 102 into an image signal so that raster scanning can be performed, and controls a printer engine 104 through an interface. The controller 103 and the engine 104 are both housed in the same printer housing.

Each part in the printer controller 103 is as follows.

103a: display unit on the surface of the printer housing 103b: operation unit on the surface of the printer housing 103c: controller CPU 103d: ROM storing operation programs in the CPU 103c 103e: temporary data in the CPU 103c Is stored in the RAM.

In FIG. 1, a printer controller 1
The user operates the operation unit 103b in accordance with the operation guide displayed on the display unit 103a in the printer 03, the printer engine 104 operates, and notifies the host computer 102 connected to the printer controller 103 of the operation state. The information is displayed on the display 101 according to the notified information.

FIG. 2 is a mechanical configuration diagram of the engine of the first embodiment. The printer comprises a main body 201 and an optional paper feeder 202 which is an option.

In FIG. 1, reference numeral 203 denotes a front cover, which is opened to open an MPT (Multi-Pu
rpose Tray) 204 can be used. Reference numeral 205 denotes a flag of a sensor for detecting the presence of a sheet on the MPT. 206 is M
M for transporting the paper on PT204 into the printer
It is a PT paper feed roller.

Reference numeral 207 denotes a PCT which is a standard paper feeding unit.
(Paper Cassette Tray). Reference numeral 208 denotes a sensor flag for detecting the presence of a sheet on the PCT. 209 is P
P for transporting the paper on CT 207 into the printer
It is a CT paper feed roller.

Reference numeral 210 denotes an optional paper feeding unit O
PT (Optional Paper cassette Tray). 211
Is a sensor flag for detecting the presence of a sheet on the OPT. Reference numeral 212 denotes an OPT paper feed roller for conveying the paper on the OPT 210 to the inside of the printer.

Reference numeral 213 denotes rollers for further conveying the paper fed from the PCT and OPT to the inside of the printer.

The sheet fed from any one of the MPT, PCT, and OPT has its leading edge abutted against the registration shutter 214 to correct the transport direction. When a predetermined transport force is applied, the transport direction is further increased. The sheet is conveyed by reaching the previous conveying roller 215. Transport roller 2
Immediately after 15 the flag 2 of the sensor called TOP sensor
16 for synchronizing the image to be conveyed with the image.

Reference numeral 217 denotes a well-known toner cartridge. Primary charging roller 218, photosensitive drum 21
9. A developing cylinder 220 is provided inside. 221 is a transfer roller.

To write the electrostatic latent image, a predetermined laser beam is irradiated on a polygon mirror 224 rotated and driven by a motor 223 in the scanner unit 222.
By irradiating the photosensitive drum 219 with the folding mirror 225.

After the paper has passed the toner transfer position, the fixing belt 227 and the pressing roller 2
28, where the toner image is fixed on the paper.

A paper discharge sensor 229 detects the presence of paper immediately after the fixing device.

The sheet that has passed through the fixing device is further conveyed by a sheet discharging roller 230. Face Up Tray 2
When the sheet 31 is open as shown in the figure, the sheets are stacked on the tray 231. When the tray 231 is closed, the prepared paper reaches at least 232 and is stacked on the face-down tray 233.

Reference numeral 234 denotes an upper door. When the upper door is opened upward, the toner cartridge 217 can be taken in and out.

FIG. 3 is a schematic diagram when the image forming operation of the present embodiment is performed. As described earlier with reference to FIG. 2, the element 301 capable of emitting a plurality of lasers is reflected by the rotating polygon mirror 302, and is irradiated on the photosensitive drum 305 by the return mirror 304 via the lens 303. The light-receiving element 306 detects a writing start reference position in the main scanning direction of the image. This light receiving element 306 is called a BD sensor. The light output of the semiconductor laser of each color is modulated in accordance with an image signal, for example, in accordance with an RGB image signal, and scanning is performed in the main scanning direction by a rotating polygon mirror 302 to expose a photosensitive drum 305.

Here, the control of the printer engine 104 of this embodiment will be described with reference to FIG. BD sensor 3
In response to the timing detection signal 405 radiated at 06, the control circuit 404 of the printer engine sends an instruction to irradiate the laser 401 from the element 301 to the laser drive circuit 403, whereby the laser 401 starts to irradiate. When this laser is detected by the BD sensor 306,
A detection signal 405 is sent to the control circuit 404 of the engine. This detection signal is called a BD signal.

At the same time that the BD signal for the laser is detected, the control circuit 404 sends a command to stop the irradiation of the laser 401 to the laser drive circuit 403, and the irradiation of the laser 401 stops. Then, the irradiation of the laser 402 is started immediately. Therefore, it is possible to detect the respective writing reference positions for the two lasers. This timing is shown in FIG. The laser 40
Reference numeral 1 denotes a laser for forming an odd-numbered image in the sub-scanning direction, and laser 402 denotes a laser for forming an even-numbered image.

In actuality, the circuit configuration of the BD sensor 306 is as shown in FIG. 6. When the photodiode 601 receives light from the laser 7 and charges are applied, and when the light is no longer received, the resistance is reduced. It is discharged with a time constant according to the value of 602. Due to this time constant, the BD signal 405 becomes dull at the time of rising, and actually has a waveform 501. According to FIG.
1. The voltage of the series load resistor 602 is changed to the reference potential 604.
The comparison circuit 603 outputs a positive voltage when the potential becomes higher than the reference potential 604.

In order to round the waveform 501 shown in FIG. 5, the BD sensor is provided with a forced discharge circuit.

FIG. 7 is a schematic diagram of the forced discharge circuit according to the first embodiment. After the photodiode 601 detects the light reception of the laser 401, the photodiode 601 transmits the BD 401 to the control circuit 404. Upon receiving the BD signal 405, the control circuit 40
4 transmits a forced discharge signal 701 to the BD sensor 306. The FET 702 is driven by this forced discharge signal 701 to perform discharge. After that, the forced discharge signal 701 is released before the light reception of the laser 402 is detected. Then, the second BD signal is transmitted to the control circuit 404 by detecting the light reception of the laser 402. With this operation, it is possible to eliminate the influence of the rounding at the rising of the BD output signal.

After the rounding is released, the next laser 40
2 can be accurately detected.

(Second Embodiment) The control of the second embodiment of the present invention will be described with reference to FIG. Embodiment 1
However, as described above, as shown in FIG.
At the timing of irradiating the laser element 06, the control circuit 404 of the printer engine sends the laser 4
A command to irradiate 01 is sent to the laser drive circuit 403, whereby the laser 401 starts irradiating. When the BD sensor 306 detects this laser, a detection signal 405 is sent to the control circuit 404 of the engine. At the same time that the BD signal 405 for the laser is detected, the control circuit 404 sends a command to stop the irradiation of the laser 401 to the laser driving circuit, and the irradiation of the laser 401 stops. Then, the irradiation of the next laser 402 is started immediately. In the BD sensor 306, a one-shot multivibrator circuit 801 using the detection signal 405 is provided. After receiving irradiation of the laser 401, the FET 702 is driven to discharge the electric charge charged in the photodiode 601. The one-shot multivibrator circuit 801 is set so that the driving time of the FET 702 is shorter than the time from when the BD sensor 306 receives the laser 401 to when the irradiation of the laser 402 is started.

As a result, the irradiation of the laser 401 starts, the light is received by the photodiode 601, and the one-shot multivibrator circuit 801 is operated by the output signal of the BD signal 405 to drive the FET 702, and Short-circuits the accumulative capacitance component that generated the.
Thereby, the rounding shown in FIG. 5 can be removed.

(Third Embodiment) The control of the third embodiment of the present invention will be described with reference to FIG. In the present embodiment, a Schmitt trigger circuit 901 is used for the one-shot multivibrator circuit 801 used in the second embodiment.

As described in the first embodiment, as shown in FIG. 4, at the timing of irradiating the BD sensor 306, the printer engine sends the laser 40 from the element 301.
1 is sent to the laser drive circuit 403,
Thereby, irradiation of the laser 401 is started.

The laser 401 is received by a photodiode 601 and a comparison circuit 60 is provided in accordance with an increase in received light.
When 3 is inverted and the BD sensor 306 detects, the detection signal 405 is sent to the control circuit 404 of the engine. At the same time when the BD signal 405 for the laser 401 is detected, the control circuit 404 sends a command to stop the irradiation of the laser 401 to the laser driving circuit 403, and the irradiation of the laser 401 stops. And immediately laser 40
The irradiation of No. 2 is started. In the BD sensor 306,
Schmitt trigger circuit 901 using detection signal 405
After receiving the irradiation of the laser 401, the FET 7
02 is driven to discharge the charge charged in the photodiode 601.

The Schmitt width of the Schmitt trigger circuit 901 is set so that the drive time of the FET 702 is shorter than the time from when the BD sensor 306 receives the laser 401 to when the irradiation of the laser 402 is started.

[0039]

As described above, the beam detector according to the present invention forcibly discharges the electric charge charged in the semiconductor light receiving element by the external controller after the scanning beam enters the light detecting means. Therefore, in an apparatus using a plurality of beams, high-speed image output can be realized.

Further, the beam detecting device according to the present invention can forcibly discharge the electric charge charged in the semiconductor light receiving element in the detecting device after the scanning beam enters the light detecting means. In an apparatus using a plurality of beams, high-speed image output can be realized.

[Brief description of the drawings]

FIG. 1 is an electric block diagram of a laser printer used in the present invention.

FIG. 2 is a schematic view of an apparatus of a laser printer used in the present invention.

FIG. 3 is a schematic diagram of laser control used in the present invention.

FIG. 4 is a control block diagram of the present invention.

FIG. 5 is a timing chart of the present invention.

FIG. 6 is a schematic view of a conventional control.

FIG. 7 is a control schematic diagram in the first embodiment.

FIG. 8 is a control schematic diagram in the second embodiment.

FIG. 9 is a schematic control diagram in the third embodiment.

[Explanation of symbols]

 Reference Signs List 201 laser printer main body 301 plural laser light emitting elements 206 laser beam detector 404 external controller 405 laser beam detection signal 601 photodiode 602 resistive load 801 one-shot multivibrator circuit 901 Schmitt trigger circuit

Claims (5)

[Claims] A light detecting means for converting a scanning beam from a scanning beam generating means into a current; a resistive load connected to the light detecting means; a semiconductor switch connected in parallel to the resistive load; Comparing means for comparing a terminal voltage of a load with a predetermined voltage, and a signal line for controlling the semiconductor switch from an external control device, wherein the scanning beam generating means is provided after the scanning beam is incident on the light detecting means. Stop outputting a beam, and after a predetermined time after the output of the comparing means has been activated, the external control device activates the semiconductor switch so as to reduce the terminal voltage of the resistive load. A beam detector characterized in that it operates. 2. A photodetector for converting a scanning beam from a scanning beam generator into a current, a resistive load connected to the photodetector, a semiconductor switch connected in parallel to the resistive load, and a resistor. Comparing means for comparing a terminal voltage of a load with a reference voltage, and a one-shot multivibrator triggered by an output of the comparing means, wherein the scanning beam generating means includes a beam after the scanning beam is incident on the light detecting means. Is stopped, and the semiconductor switch is activated by activating the one-shot multivibrator a predetermined time after the output of the comparison means is activated by the scanning beam being incident on the light detection means. A beam detector that acts to reduce the terminal voltage of the resistive load. 3. A scanning beam generating means for scanning a light beam modulated by an electric signal, a light detecting means for converting a scanning beam output by the scanning beam generating means into a current, and a light detecting means connected to the light detecting means. A resistive load, a semiconductor switch connected in parallel to the resistive load, a comparing means for comparing a terminal voltage of the resistive load with a reference voltage,
A Schmitt trigger circuit using the output of the comparing means, wherein the scanning beam generating means stops outputting the beam after the scanning beam is incident on the light detecting means, and the output of the comparing means becomes active. The beam detection device according to claim 1, wherein the semiconductor switch is activated by activating the Schmitt trigger circuit after a predetermined period of time, thereby reducing the terminal voltage of the resistance load. 4. A laser printer including a printer controller and a printer engine, wherein the printer engine includes a photodetector for converting laser beams from a plurality of laser beam generators into a current, and a photodetector connected to the photodetector. A resistive load, a semiconductor switch connected in parallel to the resistive load, comparison means for comparing a terminal voltage of the resistive load with a predetermined voltage, and a signal line for triggering the semiconductor switch. The laser beam generating means stops outputting a beam after the light enters the light detecting means, and activates the semiconductor switch from the signal line a predetermined time after the output of the comparing means becomes active. Thereby reducing the terminal voltage of the resistive load. Printer. 5. The laser printer according to claim 4, wherein said signal line activates said semiconductor switch through a one-shot multivibrator or a Schmitt trigger circuit to an output of said comparing means.