JPH03198074A - Laser beam printer - Google Patents

Abstract

PURPOSE:To carry out APC (Auto Power Control) without affecting an image by providing a variable means to extend the time of spot unblanking to be longer than at normal times when carrying out APC between one piece of paper and another and a generating means of its timing. CONSTITUTION:A pulse width of spot unblanking signal is varied with hardware by turning ON paper spacing signal 40 which shows the spacing between one piece of paper with another with CPU 7 by spot unblanking signal generating part 38, and data UBS 2 which is equivalent to the starting position of the spot unblanking between paper is set in a resister 33 beforehand by the CPU 7. At that time, light pulse is generate by AND gate 31, the light pulse is outputted from the light pulse from the CPU 7 and the signal from an address recorder 1, the spot unblanking start data and the spot unblanking finish data are latched by resisters 115 and 116, and the spot unblanking starting data is switched over to UBS 1 or UBS 2 by a selective circuit 36. Thus APC can be carried out without giving any adverse effects to an image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to light amount control of a laser beam printer.

[Prior Art] FIG. 6 is a block diagram illustrating the image forming operation of a conventional laser beam printer.

The image signal (VDO signal) 101 is transmitted to the laser unit 10
The laser beam 102 outputs a laser beam 103 that is modulated on and off based on the VDO signal. The motor 104 is a rotating polygon mirror.
105 is rotated at a constant speed to deflect the laser beam 103 and generate a laser beam 107.

The imaging lens 106 focuses the laser beam 107 on the photosensitive drum 108. Therefore, the laser beam 107 modulated by the 1-image quality code 101 is transmitted to the photosensitive drum 10.
8 is horizontally scanned (scanned in the main scanning direction).

The beam detector 109 has a photoelectric conversion element 110, for example a photodiode, and outputs a horizontal synchronization signal (hereinafter referred to as a BD signal) 111 which is the image writing timing.

The latent image formed on the photosensitive drum 108 is visualized as a toner image by a developing device (not shown), and this toner image is transferred onto the transfer paper 112 by a transfer device (not shown).

Next, the operation of each part will be explained.

A laser beam 102 generates a laser beam 103 modulated based on the input image signal 101. vD
The O signal 101 is generated from a control section (not shown) inside the laser beam printer. Modulated laser beam 103
is deflected by a polygon mirror 105 (rotating at a constant speed) having a plurality of mirror surfaces driven by a motor 104. The deflected laser beam 107 scans over the photosensitive drum 108 at a constant speed.

Further, the laser beam 107 is focused onto the photosensitive drum 108 by the imaging lens 106 .

When the photosensitive drum 108 rotates at a constant speed and the laser beam 107 scans at a constant speed, a latent image based on the VDO signal 101 is formed on the photosensitive drum 108. At this time, the laser beam 107 is incident on the photoelectric conversion element 110 of the beam detector 109 fixed near the scanning start position, and the BD signal 11 outputted from this beam detector 109
The image position on the photosensitive drum 108 in the main scanning direction is defined by generating the VDO signal 101 for l scanning in synchronization with the VDO signal 101.

Next, signals for forming an image will be explained using FIG. 7.

As described above, the BD signal 111 is a synchronization signal in the main scanning direction. FIG. 7 shows the output timing in the main scanning direction (horizontal direction) to the transfer paper 112, and shows the output timing of the BD signal 11.
When the image signal 101 is output ti after the rising edge of the signal 1, an image is formed at a position Dl from the left end of the transfer paper 112.

Of course, as described above, the image of the laser beam 107 is not directly formed on the transfer paper 112 but on the photosensitive drum 108.

The image signal 101 is output from an image processing device (not shown) such as an image processor that is separate from the control device that controls the image forming sequence. The control device uses an image mask signal 113 to mask the image processing device so that it does not expose outside the image area (area other than D2 in FIG. 7) even if the image signal 101 is turned ON.

As mentioned above, the BD signal 111 is transmitted to the beam detector 10.
Since the signal is generated when the laser beam 107 scans the beam detector 109, the control device needs to forcibly turn on the laser at the time when the laser beam 107 is expected to scan the beam detector 109. This signal is the unblanking signal 114 (see FIG. 7).

These mask signals 113 and unblanking signals 11
4 is generated by counting the system clock 124, as shown in FIG.

Next, FIG. 8 will be explained.

The BD signal 111 from the beam detector 109 is shaped by a waveform shaping circuit 123 into a pulse waveform equivalent to one pulse of the system clock 124 . This molded BD
The signal clears the main scanning counter 122. The main scanning counter 122 counts up in synchronization with the system clock 124, and is cleared every time there is a pulse of the BD signal. That is, by knowing the value of the main scanning counter 122, it can be determined which position of the laser beam 107 is being scanned.

Unblanking start data and unblanking end data are latched into the unblanking start signal generation register 115 and the unblanking end signal generation register 116 through data lines 127 and 128, respectively. Strobe pulses 125 and 126 are pulses used to latch into the two registers 115 and 116. Comparators 117 and 118 compare the contents latched in the above registers 115 and 116 with the contents of the main scanning counter, and the unblanking start signal is sent from the gate 119 and the unblanking end signal 130 is sent from the gate) 120 to the flip-flop 121. Output to.

An unblanking signal 114 is generated from these signals as shown in FIG.

Next, regarding the image mask signal 113, this signal can also be generated by the same circuit as the unblanking signal 130 described above.

In the explanation of FIG. 6 above, in order to simplify the explanation, it was explained that the laser chip 102 is turned ON and OFF by one image value number 101, but in reality, as shown in FIG. 102, an image mask signal 113, an unblanking signal 114 . It is necessary to AND and OR with the laser forced lighting signal 131.

Thereby, the image signal 101 can be formed only in the image area D2. Here, the laser forced lighting signal 131 is
This is a signal for the control device to forcibly turn on the laser.

Next, APC (Auto Power Control)
rol) will be explained. The relationship between the current supplied to a laser chip and the optical output differs from chip to chip, and also changes depending on the heat generated by the chip itself, so it is not possible to emit laser light with simple open-loose constant current control. It is necessary to monitor and control to obtain the desired light output level. This control is called APC.

Next, details of APC will be explained.

FIG. 11 is a circuit diagram showing the laser control circuit.

This laser control circuit includes a constant current circuit 133.

It is composed of a switching circuit 135 and an amplifier 138.

The constant current circuit 133 is a voltage-current converter, and the switching circuit 135 is a circuit for causing a current 11 to flow according to a light amount signal 134 from the control device, and for switching this using the laser lighting signal 132. In response to the operation of this switching circuit 135, a laser 136 emits light.

The amount of light emitted is extracted as a current value by a photodiode 137, and converted into a voltage signal by a resistor 140.

The light emission amount extracted as a voltage value is amplified by an amplifier 138 and becomes a light emission amount signal 139.

The control device increases the level of the light amount signal 134 while monitoring the light amount signal 139.

FIG. 12 is a flowchart showing this APC operation.

This control begins with the laser forced lighting signal 131 in FIG.
After activating the light intensity signal 139 (Sl), if the light intensity is lower than the desired value, increase the level of the light intensity signal 134 by one step (S2), and conversely if it is higher than the desired value. To do this, the level of the light intensity signal 134 is lowered by one step (S3), and if the light emission level is at the desired value, Arc! Finish the work b.

During this time, the laser beam scans the area corresponding to the arrow in FIG.

This APC is performed not only at the beginning of image formation, but also at the portion between sheets when printing a plurality of sheets in succession.

On the other hand, as shown in FIG. 14, APC may be performed outside the image area. This method is used when the light intensity level is guaranteed for each line, or when creating a line between sheets of paper as shown in FIG. 13 affects image formation. This method utilizes the unblanking period described above.

[Problems to be Solved by the Invention] However, among the conventional examples described above, in the method shown in FIG. If the rollers are placed along the same line, the rollers become dirty, which affects the image.Therefore, in order to prevent this, the sequence of charging the photosensitive drums has to be complicated.

Furthermore, in a method using an unblanking period as shown in FIG. 14, the responsiveness of the light emission amount signal 139 becomes a problem in high-resolution machines or high-speed machines with a short unblanking period.For example, as shown in FIG. Assuming that t2 is the period until the output of the light emission quantity number 139 converges to the output Pa corresponding to the output of the laser diode 138, the laser emission control cannot be performed unless the unblanking period is longer than t2. .

Furthermore, if the unblanking time is increased, the edge of the polygon mirror 105 will be hit by the laser beam, and as a result,
Scattered light is irradiated onto the photosensitive drum.

This had the disadvantage that it had a negative effect on the image.

The present invention enables even an apparatus with a high scanning speed to
It is an object of the present invention to provide a laser beam printer that can perform APC with simple control without adversely affecting images.

[Means for Solving the Problems] The present invention provides a laser that forms an image based on a horizontal synchronization signal that is output when the laser beam passes through a beam detection means by forcibly lighting a laser outside the image forming area. In the beam printer, a variable means for varying the forced lighting time outside the image area, and when the irradiation position of the laser beam on the photoreceptor is scanning a portion corresponding to between transfer sheets, It is characterized by comprising a light amount control means for controlling the amount of light by varying the forced lighting time by the variable means within a range that does not cover the image forming area.

[Function] The present invention provides a variable means for making the unblanking time longer than the normal time when performing APC between sheets of paper, and a means for generating the timing thereof.
Even with high-resolution machines or high-speed machines with fast scanning speeds, Arc can be performed without requiring a complicated charging sequence between sheets and without affecting image quality.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of the present invention. Note that the configuration is similar to the above conventional example.

The same symbols are attached.

In FIG. 1, the unblanking signal generating section 8 performs the same operation as described above.

The CPU 7 includes an unblanking start signal generation register 115 and an unblanking end signal generation register 1.
Set the data to 16. The address decoder 1 and the AND gate 3. generate the write pulse at that time.
It is 4. Further, 2 is a system clock generation circuit, and 5 is a BD signal generation section.

FIG. 2 is a flowchart explaining the operation of this embodiment. Note that operations unrelated to the present invention will be omitted from the flowchart for explanation.

First, after starting image formation, unblanking start data (UBSI) is set (S10). This data value is set at a of the unblanking start position 29 shown in FIG.
Unblanking end data (UBE) is set (s t i) to the 0th order, which is a value corresponding to the position of , and this value is a value corresponding to the unblanking end position 30 shown in FIG.

Next, the laser forced lighting signal 131 is turned on (S 12
) However, at this point, the light amount signal 134 is not set, so no current flows through the laser diode 136 and it does not emit light. In this state, the light amount signal 134 is increased by one step (S13), and then, at time t2. Wait for the elapse of (S14), this is the 11th
This is to secure time until the amount of light emitted by the laser diode 136 is changed by changing the light amount signal 134 in the system shown in the figure, and the change in the amplifier 138 is completed.

Thereafter, it is determined whether the 1-light emission amount signal 139 has reached the desired value (S15). If it has not reached the desired value, the operation of increasing the light amount signal 134 by 1 step and then checking the light emission amount (S13.515) is performed. This is repeated until the light emission amount signal 139 reaches the desired value.

When the laser diode 136 starts emitting light with the required amount of light through this operation, the forced laser lighting signal 131 is turned off (s16). From then on, the laser diode 136 will not emit light unless the image signal 101 is input.
At this point, image formation is possible.

Next, after forming an image based on the image signal 101 from the outside (517), it is determined whether or not there is a second print (S18). The amount signal 139 is turned off (528) and the process ends.

In addition, if there is a second print, data corresponding to position b of the unblanking start position 29 in FIG. 3 is set as unblanking start data (S
19) Next, wait until the unblanking signal 121 is input (S20), and when the unblanking signal 121 is input, wait until the time t2 has elapsed due to the above-mentioned reason (S21), and compare the light emission amount with the target value. (S22).

As a result, if the light emission amount is higher than the target value, the light amount signal 134 is lowered by one step (S24).

If the amount of light emission is lower than the target value, the light amount signal 134 is increased by one step (S23), and this process is continued until the amount of light emission becomes equal to the target value.

When the light emission amount becomes equal to the target value, the unblanking start data is returned to the original value (UBSI) (S25
), image forming processing is performed (S26), thereby making it possible to prevent the laser beam from hitting the edge of the polygon mirror 105 during the image forming period and the scattered light from affecting the image.

After that, check whether there is a printout for the next page.527
), if there is, return to 519 and perform Arc; if not, turn off the light emission amount signal 139 (528).

The above processing enables accurate laser light amount control and high-quality image formation.

In the previous embodiment, a case has been described in which the CPU performs APC in synchronization with the timing of the unblanking signal using software, but a more hardware-based configuration may be used in other embodiments.

FIG. 4 is a circuit diagram illustrating an embodiment in such a case.

The unblanking signal generating section 38 is a circuit that changes the pulse intensity of the unblanking signal using hardware when the CPU turns on a paper gap signal 40 indicating the gap between sheets.

The CPU 7 stores in advance data (UBS2) corresponding to the unblanking start position in the paper interval in the register 33.
Set it to .

The AND gate 31 generates the write pulse at that time, and outputs the write pulse from the write pulse from the CPU 7 and the signal from the address recorder 1. Registers 115 and 116 contain unblanking start data (UBS
I) and unblanking end data (UBE) are latched.

The main scanning counter 122, waveform shaping circuit 123, and system clock generating section 2 are the same as those described above.

The selection circuit 36 selects the unblanking start data from the UBS.
This is a circuit for switching to I or UBS2.

FIG. 5 is a circuit diagram illustrating details of the selection circuit 36.

The CPU 7 turns on the paper interval signal 40 at a position corresponding to the paper interval (a position where APC is performed between the papers). Further, in this circuit, a latch 41 is used to obtain a synchronizing signal in order to perform the operation of switching the unblanking start signal in synchronization with the unblanking signal. In other words,
UBS2 and UBSI are switched when the output from the latch 41 is "H" and when it is "L".

By using this method, the load on the CPU can be reduced and APC during unblanking can be easily performed.

Further, in the above embodiment, the start position of the unblanking signal is changed, but the unblanking end position may also be changed. By doing so, APC during sheet unblanking at higher speed scanning becomes possible. Further, the unblanking start position in FIG. 3 may be changed depending on the paper size. Note that such processing can be specifically realized in the same manner as in the above-mentioned embodiment, so detailed explanation will be omitted. Omitted.

[Advantageous Effects of the Invention 1] As explained above, according to the present invention, even if the resolution and speed of laser beam printers become higher, stable laser light amount control can be performed, and furthermore, the image forming area between sheets will not be exposed to light. Therefore, high-quality images can be formed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is a flowchart showing the operation of the same embodiment. FIG. 3 is a schematic diagram showing unblanking in the same embodiment. FIG. 4 is a circuit diagram showing another embodiment of the present invention. FIG. 5 is a circuit diagram showing an unblanking switching circuit in the same embodiment. FIG. 6 is a configuration diagram illustrating an example of the prior art. FIG. 7 is a time chart illustrating image-related signals in the conventional example. FIG. 8 is a circuit diagram showing an unblanking generation circuit in the conventional example. FIG. 9 is a time chart showing the operation of the unblanking generation circuit in the conventional example. FIG. 10 is a circuit diagram illustrating a laser lighting signal in the conventional example. FIG. 11 is a circuit diagram illustrating a laser emitting circuit in the conventional example. FIG. 12 is a flowchart illustrating APC in the conventional example. FIG. 13 is a schematic diagram illustrating the laser beam scanning position during APC in the conventional example. FIG. 14 is a schematic diagram illustrating another example of the laser beam scanning position during APC in the conventional example. FIG. 15 is a schematic diagram illustrating a light emission amount signal in the conventional example. l...Address decoder, 2...System clock generation circuit, 3. 4...AND gate, 5...BD signal generation section, 7...CPU, 8...Unblanking signal generation section.

Claims (1)

[Scope of Claim] A laser beam printer that forms an image based on a horizontal synchronization signal output when the laser beam passes through a beam detection means by forcibly lighting a laser outside the image forming area, comprising: a variable means for varying the forced lighting time outside the image area; when the irradiation position of the laser beam on the photoreceptor is scanning a portion corresponding to between transfer sheets, the variable means forcibly turns on the light; A laser beam printer comprising: a light amount control means for controlling the light amount by varying the lighting time within a range that does not cover the image forming area;