JPH04189560A - Image formation device - Google Patents

Abstract

PURPOSE:To control power automatically with a simple operation by providing timing control means for controlling light quantity in an area excepting the maximum printable area with respect to the horizontal scanning direction at an unblanking time and in an area excepting image assurance areas at front and rear ends in a record medium with respect to the vertical scanning direction. CONSTITUTION:When a light emission quantity is higher than a desired value, a light quantity signal is made to be down by 1 step. When the light emission quantity is lower than the desired value, the light quantity signal is made to be up by 1 step. This process is to be continued until the light emission quantity becomes equal to the desired value. When the light emission quantity became equal to the desired value, an unblanking start data is returned to an original value. Thereafter, a vertical synchronization request signal is outputted so as to process an image formation. Accordingly, the laser beam strikes upon an edge of a polygon mirror during the image formation so that the influence of the scattered light on the image can be avoided. Thereafter, it is determined whether a printout for a next page exists or not. When it exists, an APC is performed. If not, the light emission quantity signal is turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus such as 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
2, and the laser unit 102 outputs a laser beam 103 that is on/off modulated based on the vDO signal. A motor 104 rotates a rotating polygon mirror 105 at a constant speed, deflects a laser beam 103, and generates a laser beam 107.

The imaging lens 106 focuses the laser beam 107 onto the photosensitive drum 108. Therefore, the laser beam 107 modulated by the image signal 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 synchronizing signal (hereinafter referred to as BD double 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.

The laser unit 102 generates a laser beam 103 modulated based on the input image signal 101. V.D.
The O signal 101 is generated from a control section (not shown) inside the laser beam printer. Modulated laser beam 103
is deflected to 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, laser beam 1
07 is a beam detector 10 fixed near the silkworm starting position
The image position on the photosensitive drum 108 in the main scanning direction is determined by generating the VDO signal 101 for one scan in synchronization with the BD signal 111 inputted to the photoelectric conversion element 110 of No. 9 and output from the beam detector 109. stipulated.

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

The BD signal 111 is a synchronization signal in the main scanning direction as described above. FIG. 7 shows the output timing in the main scanning direction (horizontal direction) to the transfer paper 112.
When the image signal 101 is input t1 after t1 from the rising edge of the transfer paper 112, an image is formed at a position separated from the left end of the transfer paper 112 by a distance of .

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 masks the area (other than D2) using an image mask signal 113 so that it is not exposed even if the image signal lot is turned on.

As mentioned above, the BD signal 111 is transmitted to the beam detector 10.
Since the signal is emitted by the laser beam 107 scanning over the beam detector 109, the control device needs to forcibly turn on the laser at a time when the laser beam 107 is expected to scan over 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 8D
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 is possible to know which position the laser beam 107 is scanning.

Unblanking start data and unblanking end data are latched into the unblanking start signal generation register 115 and the unblanking start signal generation register 116 through data lines 127 and 128, respectively. The strobe pulses 125° and 126 are pulses used to latch 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 to the unblanking end signal 130 from the gate 120 to the flip-flop 121. I'll do it.

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 114 described above.

In the explanation of FIG. 6, in order to simplify the explanation, the image signal 101 is used to turn on and off the laser unit 102, but in reality, as shown in FIG. Until the image mask signal 113. It is necessary to AND and OR the unblanking signal 114 and 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)
) 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 cause laser light to be emitted simply by constant current control in an oven loop. Therefore, it is necessary to monitor the optical output and control it so that a desired optical pressure level is obtained. This control is done by APC
That's what it means.

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, a switching circuit 135, and an amplifier 138.

The constant current circuit 133 is a voltage-current converter, and flows a current 11 according to a light amount signal 134 from the control device. A switching circuit 135 is a circuit 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, monitor the light emission amount signal 139 (Sl), and if the light emission amount is lower than the desired value, increase the level of the light amount signal 134 by one step (S2), and conversely, if it is higher than the desired value, raise the level of the light amount signal 134 by one step (S2). Then, the level of the light amount signal 134 is lowered by one step (S3). Further, if the amount of light emission has reached a desired value, the APC operation is ended.

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 ensuring the light intensity level for each line, or when creating a line between sheets of paper as shown in FIG. 13 affects image formation. This method uses the previous unblanking period.

[Problem to be solved by the invention]

However, among the above conventional examples, in the method shown in FIG. 13, a line appears between the sheets, so when using the roller transfer method (in which the roller for transfer is arranged along the photoreceptor) The rollers become dirty, which affects the image. Therefore, there is a drawback that the charging sequence of the photosensitive drum becomes complicated in order to prevent this.

Further, in the 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 where the unblanking period is short. For example, as shown in FIG. 15, the output of the light emission amount signal 139 is an output P corresponding to the output of the laser diode 136. Assuming that the period until convergence is t2, 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,
There was a drawback that the photosensitive drum was irradiated with scattered light, which adversely affected the image.

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

[Means to solve the problem]

In order to achieve the above object, the present invention provides an exposure means using laser light, a laser light amount control means that controls the exposure means based on the detection result of the laser light output to adjust the laser light output to a desired level, and The light amount control by the light amount control means is the unblanking time, which is at least an area excluding the maximum printable area in the main scanning direction, and excluding image guaranteed areas at the leading and trailing edges of the recording medium in the sub-scanning direction. (It is characterized by comprising a timing control means that executes in the area.

[Function] According to the present invention, laser light amount control can be performed without degrading print quality, and BD
Failures (not true failures but apparent failures due to APC processing timeout) can be prevented.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention. It should be noted that "configurations similar to those of the above-mentioned conventional example are denoted by the same reference numerals.

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. 'Address decoder 1 and 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 (SIO). This data value is a of the unblanking start position 29 shown in FIG.
This is the value corresponding to the position of . Next, unblanking end data (UBE) is set (S11). This value often corresponds to the unblanking end position 30 shown in FIG.

Next, turn on the laser forced lighting signal 131 (S12)
.

However, at this point, the light amount signal 134 has not been 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 thereafter, at time t.

(S14), this is the above-mentioned 11th
This is to ensure the time required for the light intensity signal 134 to change in the system shown in the figure to change the intensity of the red light from the laser diode 13B and for the change in the amplifier 138 to be completed.

Thereafter, it is determined whether the light emission amount signal 139 has reached a desired value (S15). If the light intensity signal 134 has not reached the desired value, the operation of increasing the light intensity signal 134 by one step and checking the light emission amount (S13.515) 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 (S16A). Thereafter, the laser diode 136 does not emit light unless the image signal 101 is input.

At this point, image formation is possible.

Next, the vertical synchronization request signal (VSREQ) is applied at 516B to form an image based on the external image signal 101 (S17), and then it is determined whether or not a second sheet is to be printed (S18). If there is no second print, the light emission amount signal 139 is turned off (S28) and the process ends.

Furthermore, 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 (S1
9). b is determined by the following conditions in the main scanning/sub-scanning direction with respect to the transfer paper 112.

First, regarding the main scanning direction, it is determined by adding the phenomenon possible areas bl and b2 to the maximum size of the transfer paper 112 in the main scanning direction. Specifically, bl and b2 are 2 to 3 m
It is about m.

Next, regarding the sub-scanning direction, the top margin of the transfer paper 112 is al on the leading edge side and 82 on the trailing edge side, both of which are 3 m.
It is about m. Next, it waits until the unblanking signal 121 is input (S20), and when the unblanking signal 121 is input, it waits until the time t2 has elapsed due to the above-mentioned reason (S21), and compares the amount of light emission with the target value (S22). )
.

As a result, if the amount of light emitted is higher than the target value, the light amount signal 134 is lowered by one step (S24), and if the amount of light emitted is lower than the target value, the light amount signal 134 is increased by one step (S23), and this process Continue 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
A), output the vertical synchronization request signal (VSREQ)52
5B), image forming processing is performed (S26). This prevents the edge of the polygon mirror 105 from being irradiated with laser light 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, the process returns to S19 and APC is performed. If there is none, the light emission amount signal 139 is turned off (S28).

Next, APC processing (i.e., Fig. 2 (1)
) and (2)) are not completed, the flowchart in FIG. 2 (3) shows the control method.

In addition, FIG. 3 (2) shows a video controller (not shown)
This is a schematic representation of the relationship between A'PC control and A'PC control centering on control signals for the printer.

Among these, t4 indicates the time from the start of APC to the output of VSREQ, which is a request signal for a vertical synchronization signal of video data, at an original predetermined timing (unique timing for maintaining maximum throughput).

At t6, since APC has not ended even after t4, if APC ends within this time, immediately
By outputting the VSREQ signal, a predetermined printing operation becomes possible. t is a value determined in advance based on the current characteristics, slope efficiency, optical pressure, thermal characteristics, lifetime, etc. of the laser diode. Actually, it is about 0.5 to 1 sec.

First, it is determined in S29 whether t4 has elapsed, and if it has not elapsed, it is determined in S30 whether there is a second print, and if so, the process advances to S21, otherwise the process advances to S13.

If t4 has elapsed in S29, it is determined in S31 whether t has elapsed, and if it has not elapsed, APC is performed in S32.
Determine whether or not it is delay mode, and if so, go to S30, otherwise go to S33 to send vertical synchronization request signal (VSREQ)
The output is delayed for a predetermined period of time, and then the APC delay mode flag is set in S34, and the process proceeds to S30. t in S31.

If the elapsed time has elapsed, failure processing due to APC delay is performed in S35, and the process ends. This failure processing means that the horizontal synchronization signal of the video data (
This process is performed when the BD multiplied signal cannot be generated, and is called BD failure.

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

<Second example> Next, a second example will be described.

FIG. 4 is a flowchart showing the second embodiment.

(The reference numbers in the figure indicate connections to those in Figure 3, and the same processing step numbers as in Figure 3 indicate the same processing.)
. According to this, when APC is delayed (S32), that is, when the above-mentioned t4 has elapsed, if the laser light amount at that time is more than a predetermined light amount (90% or more of the target light amount), (3
36), by treating it as an isometric target value (that is, to 525B), the vertical synchronization signal request signal VSREQ is set to 8, assuming that APC has ended.

If the laser light intensity does not reach the predetermined light intensity or more before t passes in S31, it is assumed that AP and C have been delayed, and failure processing is executed (S35).

The predetermined amount of laser light referred to herein is a level that guarantees the lowest printing quality, and is determined by the process conditions of electrophotography.

Therefore, it depends on the recording medium and environmental conditions, and these can also be set as parameters, and the value is about 90% of the target light amount.

The feature of this embodiment is that the vertical synchronization signal request signal (VSRE
Q) can be output with minimal delay, so APC processing can be executed with almost no effect on throughput.

The above processing makes it possible to accurately control the amount of laser light and form a high-quality image, similar to the example described above.

<Third Example> A flowchart explaining the third example is shown in FIG. 5 (numerals in the figure are the same as in the description of conditions in FIG. 4).

In this embodiment, at the time t4 has elapsed, it is determined whether or not the BD is out of stock (S37).

First, when a BD fails (the laser light intensity is low and has not reached a level that can be detected by the BD), the vertical synchronization signal request signal (VSREQ) is delayed by a predetermined period of time to extend the APC processing time. Plan. As a result, the possibility of continuation of the printing operation on the paper is increased.

Next, if there is no BD failure, the light level is at least detectable by the BD, so if it is above the target light intensity (S36 →
S38.539), printing on the paper is possible.

If it is less than that, the process returns to S31, and since the print quality cannot be maintained, the vertical synchronization signal request signal (VSREQ) is delayed by a predetermined time to extend the APC processing time.

In this embodiment, in S39, it is notified that the laser has reached the end of its life,
The feature is that the user interface has been improved.

In other words, if the minimum image quality is satisfied, printing on the second and subsequent sheets is permitted, and a notification is given that the laser's lifespan will soon reach its end.

The above processing makes it possible to accurately control the amount of laser light and form a high-quality image, similar to the example described above.

【Effect of the invention〕

According to the present invention, even as resolution and speed increase, stable light amount control is possible and high-quality images can be formed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. FIG. 2 is a flowchart showing a first embodiment of the present invention. FIG. FIG. 4 is a schematic diagram showing the ranking; FIG. 4 is a flowchart showing the second embodiment of the present invention; FIG. 5 is a flowchart showing the third embodiment of the invention; FIG. 6 is an example of the prior art. 7 is a time chart illustrating image-related signals in the conventional example, FIG. 8 is a circuit diagram showing an amplifier ranking generation circuit in the conventional example, and FIG. 9 is a circuit diagram illustrating an amplifier ranking generation circuit in the conventional example. 10 is a circuit diagram showing the laser lighting signal in the conventional example. FIG. 11 is a circuit diagram showing the laser emitting circuit in the conventional example. , a flowchart showing APC in the conventional example, FIG. 13 is a schematic diagram illustrating the scanning position of the laser beam during APC in the conventional example, and FIG. 14 shows the scanning position of the laser beam during APC in the conventional example. FIG. 15 is a schematic diagram illustrating a light emission amount signal in the conventional example. DESCRIPTION OF SYMBOLS 1... Address decoder, 2... System clock generation circuit, 3.4... AND gate, 5... BD signal generation part, 7... CPU, 8... Unplugging signal generation part. Figure 2 (2) Figure 2 (3) No. 61 J! b4#, '8101 A □ Figure 7 Voice 11th Figure 13 Figure 14 Figure 15

Claims (1)

[Scope of Claims] 1) Exposure means using laser light; Laser light amount control means that controls the exposure means based on the detection result of the laser light output to bring the laser light output to a desired level; and the light amount The light quantity control by the control means is an unblanking time, which is at least an area excluding the maximum printable area in the main scanning direction, and an area excluding image guaranteed areas at the leading and trailing edges of the recording medium in the sub-scanning direction. 1. An image forming apparatus comprising: a timing control means for executing the image forming apparatus. 2) In claim 1, the timing control means includes a light amount control end determining means for determining whether or not the laser light output reaches a desired level within the timing at which the laser light amount control means executes the light amount control. and means for extending the output request signal of the vertical synchronization signal to a predetermined desired time based on the determination result of the light amount control end determination means.