JPH0615872A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] During the resolution changing period, it is possible to shift to the image forming operation in a short time without completely turning off the laser diode, and a high-quality, high-performance image can be obtained without laser scanning the photosensitive region. Allows formation. [Structure] A second timer 21 for controlling the rotation speed of the polygon mirror 3 is set to a value according to the resolution to be changed, and then the first timer 20 performs interrupt processing to the CPU 16 for a certain period of time. Let During the interrupt, it is determined whether or not the polygon mirror 3 has reached the target value, and when the predetermined number of rotations is reached, the printing operation is started. In addition, the laser diode 4 is turned on shortly before the set value is counted up so that the printing operation can be quickly started without laser scanning the photoconductor region.

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 which is applied to a laser printer or the like and which scans an image carrier by a rotating polygon mirror with a laser beam.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional laser printer, in which 1 is a drum-shaped photosensitive member as an image carrier and 2 is f.theta.
A lens 3 is a polygon mirror which is a rotary polygon mirror, 4 is a laser diode (LD) which is a laser light source for emitting a laser beam L, and 5 is beam detection means which detects the laser beam L reflected from the polygon mirror 3. Photo detector,
Reference numeral 6 is a driver for the LD 4, and reference numeral 7 is a logic circuit section including an AND circuit and an OR circuit.

Further, 10 is a reference clock (CLK) counter, 11 is a data latch section, 12 is a decoder section, 13 and 14 are ROM and RAM as memories, and 15 is a pulse generator for controlling the rotation of the polygon mirror 3. Used as a timer,
Reference numeral 16 is a CPU (central processing unit) for controlling the above-mentioned members, and 17 is a data bus.

In FIG. 4, a pulse having a cycle set by the CPU 16 is output to the drive unit of the polygon mirror 3, and the polygon mirror 3 rotates at a rotation speed proportional to the cycle of this pulse. The laser beam L emitted from the LD 4 is reflected by the polygon mirror 3 and passes through the fθ lens 2 to form the photosensitive member 1.
The surface is scanned to form a latent image on the surface of the photoconductor 1.

By changing the number of rotations of the polygon mirror 3 while keeping the rotation speed of the photoconductor 1 constant, the pitch (resolution) of the photoconductor 1 in the sub-scanning direction can be changed.

Further, in order to align the writing positions of the scanning lines on the photosensitive member 1, the pixel clock is generated by the signal (DETP) obtained by making the laser beam L incident on the photodetector 5 installed outside the effective image area on the scanning start side. Synchronize.

As shown in the timing chart of FIG. 5, the counter 10 is reset at the rising edge of the DETP, after which the counter 10 counts up with the reference clock and a predetermined count value (time: t) set in the decoder unit 12 is reached.
When it reaches a), LD4 is turned on. The predetermined count time ta is slightly shorter than the line cycle tb.

The output value of the counter 10 when the rising edge of DETP is input is held in the data latch unit 11. CPU
16 reads out the data held in the data latch unit 11 to check whether the polygon mirror 3 is rotating at a predetermined rotation speed.

When changing the resolution, the data set in the timer 15 is changed and the data set in the decoder section 12 is also changed. After that, the LD 4 is not turned on until the number of revolutions of the polygon mirror 3 reaches a predetermined value. In the above case, if the LD 4 is turned on before the rotation speed of the polygon mirror 3 reaches a predetermined value,
In the transitional period of the change from 300 dpi in FIG. 5 (a) to 400 dpi in FIG. 5 (c), as shown in FIG. 5 (b), the photoconductor region is partially (tx) scanned. Since this portion is developed, the toner is wasted and the image quality is deteriorated.

[0010]

In the above-mentioned prior art, when the resolution is changed, the LD 4 is not turned on and the L 4 is turned on again.
Since the timing when D4 is turned on is not synchronized, at worst one line scans the photoconductor 1. If the light amount of the laser beam L is to be adjusted while changing the resolution, the photoconductor 1 is also scanned.

Further, when it is detected that the rotation speed of the polygon mirror 3 is stable in the DETP cycle tb, even if the actual rotation speed change time is short, the worst time condition is taken into consideration and the predetermined time is the predetermined time. Since it is not possible to print, there was a problem in work efficiency.

An object of the present invention is to set the LD during the resolution changing period.
Can be switched to image forming operation in a short time without completely turning off the
Another object of the present invention is to provide a high-quality and high-performance image forming apparatus without laser scanning the photoconductor region.

[0013]

In order to achieve the above object, the present invention provides a means for causing a rotating polygon mirror to scan an image carrier with a laser beam, a beam detecting means for detecting the laser beam, and A means for starting the light emission of the laser light source after a lapse of a predetermined time from the beam detection by the beam detection means, a means for measuring the time from the beam detection to the next beam detection, and a rotation speed of the rotary polygon mirror. And a means for changing the resolution, and the laser light source can emit light even when the resolution is changed.

Further, when the resolution is changed, the predetermined time from the beam detection is changed at regular intervals.

Further, when the resolution is changed, the light amount of the laser beam is adjusted during the scanning period outside the image carrier.

[0016]

According to the above means, when the resolution is changed, the predetermined time from the beam detection to the start of laser light source emission is changed according to the change, so that the image carrier is scanned with the laser beam during the change period. Is prohibited, and the laser light source is controlled so that the laser light source can emit light even during the change period so that the image forming operation can be started immediately after the change.

Further, by changing the predetermined time at regular intervals, it is possible to confirm the change in the rotation speed of the rotary polygon mirror during the change period, and the next image forming operation can be performed immediately after the rotation speed stabilizes. Put in.

Since the image carrier region can be estimated by the predetermined time even during the changing period, the laser light amount can be adjusted by detecting the laser emission amount during the laser beam scanning period outside the image carrier region, which is preferable. Immediately enter the image forming operation.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. The members corresponding to those described with reference to FIGS. 4 and 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a block diagram of an embodiment of the present invention.
Reference numeral 20 is a first timer for performing interrupt processing to the CPU 16, and 21 is a second timer as a pulse generator for controlling the rotation speed of the polygon mirror 3 in which a value according to the resolution to be changed is set. The operation of this embodiment will be described with reference to the flowchart of the main routine of FIG. 2 and the flowchart of the interrupt routine of FIG.

When there is a request for changing the resolution (S1-1), the second
Set the value corresponding to the resolution to be changed to the timer 21 of (S1
-2), followed by a fixed period (for example, 10
Permits interrupt generation for (msec) (S1-3). afterwards,
The interrupt routine is entered at regular intervals.

An example of changing the resolution from 300 dpi to 400 dpi shown in FIG. 5 will be described below.

In the interrupt routine, first, the time tb (the number of CLKs) at that time is read from the data latch unit 11, and the latched data has a target value (for example, 750CL).
K) is determined (S2-1). If they do not match (NO in S2-1), a value obtained by subtracting a predetermined value (50 CLK) from the value read from the data latch section 11 (for example, 990 CLK) is set in the decoder section 12 as ta (940 CLK) (S2). -
2). After that, the above-mentioned tasks are performed in the interrupt routine at regular intervals (10 msec).

The value read from the data latch unit 11 gradually changes, and from that value, L is reached before a minute time (50 CLK: 100 μsec).
Since D4 is turned on, the photoconductor region is never scanned with the laser beam L.

Also during the above-mentioned resolution changing period, the photoconductor area can be estimated based on the value read from the data latch unit 11, so that the LD 4 is turned on outside the photoconductor area and the light emission amount of the laser beam is detected. Thus, the light amount of the laser beam can be adjusted.

When the polygon mirror 3 reaches the target rotation speed, the latch data coincides with the target value (S2-1
YES), a flag is set based on this determination (S2-3), and the interrupt by the first timer 20 is prohibited (S2-4).

When it is found that the flag is set in the main routine (YES in S1-4), the flag is turned off.
(S1-5), the printing operation of the next page whose resolution has been changed is permitted (S1-6).

Since the synchronization period tb is measured during the above-mentioned resolution changing period, it is not necessary to wait for the start of printing of the next page during the worst condition period as in the conventional case.

[0029]

As described above, according to the present invention,
During the resolution changing period, the scanning of the image carrier with the laser beam is prohibited, and the laser light source can emit light. Therefore, it is possible to prevent the toner from being wasted and the transfer sheet from being soiled. Immediately after the change, it is possible to improve the workability by putting it in the image forming operation.Because the change in the rotational speed of the rotary polygon mirror can be confirmed at regular intervals during the change period, the next time immediately after the rotational speed stabilizes. Since the image forming operation can be performed and the image carrier area can be estimated during the change period, the laser emission amount can be detected in the laser beam scanning period outside the image carrier area,
The amount of laser light can be adjusted without affecting the image formation, and a good image formation operation can be started immediately.For example, the image formation operation can be started in a short time without completely turning off the laser light source during the resolution change period. Further, it is possible to provide a high-quality and high-performance image forming apparatus without laser scanning the photosensitive body (image carrier) area.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a flowchart of a main routine of this embodiment.

FIG. 3 is a flowchart of an interrupt routine of this embodiment.

FIG. 4 is a configuration diagram of a conventional laser printer.

FIG. 5 is a timing chart of signal output when the resolution is changed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive member (image bearing member), 2 ... fθ lens, 3 ... Polygon mirror (rotating polygon mirror), 4 ... Laser diode (laser light source), 5 ... Photodetector (beam detection means), 6 ... Driver, 10 … Counter, 11… Data latch part, 12
… Decoder, 13… ROM, 14… RAM, 16… CP
U, 17 ... Data bus, 20, 21 ... Timer.

Claims (3)

[Claims] 1. A means for scanning an image carrier by a rotary polygon mirror with a laser beam, a beam detecting means for detecting the laser beam, and a laser light source emitting light after a lapse of a predetermined time from the beam detection by the beam detecting means. And a means for measuring the time from the beam detection to the next beam detection, and a means for changing the resolution by changing the number of rotations of the rotary polygon mirror. An image forming apparatus, wherein the laser light source is also capable of emitting light. 2. The image forming apparatus according to claim 1, wherein when the resolution is changed, the predetermined time from the beam detection is changed at regular intervals. 3. The image forming apparatus according to claim 1, wherein the light amount of the laser beam is adjusted during the scanning period outside the image carrier when the resolution is changed.