JPS6410152B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laser printer, and more particularly to a laser drive control method for stabilizing the output of a laser light source.

PRIOR TECHNOLOGY In general, the basic configuration of the optical system of a laser printer is as shown in FIG. The emitted light from the semiconductor laser 2 is converted into parallel light by the objective lens 3, and then sent to the rotating polygon mirror 4 (or a light diffraction element such as a hologram plate), where it is deflected in the main scanning X direction. The laser beam is configured to pass through an f.theta. lens 5 and form an exposure spot on a photosensitive drum 6 rotating in the sub-scanning Y direction, thereby sequentially optically recording images. In addition,
In the figure, 7 indicates a direction in which the laser beam emitted from the semiconductor laser 2 is moved before it reaches the optical recording surface on the photosensitive drum 6 in order to synchronize the optical recording on the photosensitive drum 6 in the main scanning X direction. A photodetector is shown for sensing during the scanning stage. Further, depending on the configuration of the optical system, optical elements such as a reflecting mirror, a beam expander, and a correction lens may be appropriately disposed in the path of the laser beam.

In addition, in such a laser printer, especially when the semiconductor laser 2 is used as a light source, the exposure sensitivity of the laser output light to the photoreceptor drum 6 is not very good, so high-speed exposure scanning cannot be performed. Therefore, as shown in FIG. 2a, a semiconductor laser array in which a plurality of laser elements LD1, LD2, and LD3 are arranged in an array is used as a light source, and as shown in FIG. 2b, a plurality of lines L1, L2,
L3 optical recording is performed simultaneously to increase the speed. In addition, due to structural problems, each laser element LD1, LD2, LD3
If the interval d becomes large, the interval between each main scanning line L1, L2, L3 becomes wide and the resolution in the sub-scanning direction deteriorates.As shown in FIG. Main scan LD3
This problem is solved by arranging the main scanning lines at a certain angle φ with respect to the direction so that the intervals between the main scanning lines L1 to L3 become narrower.

In a laser printer configured in this way, it is necessary to stabilize the output of the laser light source during optical recording to perform optical recording without uneven exposure. The light is detected by a photodetector (also used as a photodetector for synchronous detection), and the drive current of the semiconductor laser is adjusted according to the detection output so that the laser light always maintains a constant light intensity. I try to control it.

However, with the laser drive control means in such conventional laser printers, when the aforementioned semiconductor laser array is used as a light source, the number of photodetectors is equal to the number of laser elements, and each of them is controlled according to the detection output. If the output of each laser element is controlled independently, the output from each laser element will become uneven due to variations in the characteristics of each photodetector, resulting in uneven exposure for each scanning line. There is a problem with this.

Purpose The present invention has been made in consideration of the above points, and in order to eliminate variations in the output of each laser element in a semiconductor laser array, each laser element is A laser beam is emitted, each laser beam is detected in time series by one dedicated photodetector, and the detection output is temporally resolved to generate a signal corresponding to the intensity of each laser beam. A laser drive control method in a laser printer that performs optimal feedback control for each laser element and eliminates the influence of uneven light receiving characteristics when using multiple photodetectors as in the past. It provides:

Configuration An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In the laser drive control method according to the present invention,
First, as shown in FIG. 4, in a portion of the semiconductor laser array 9 in which a plurality of laser elements LD1, LD2, LD3 are arranged on one heat sink 8, the laser beams B1, B2,B
Monitor output lights b1, b2, b3 generated from the rear of each laser beam when firing 3 (1/1/2 of the normal laser light output)
(having a light intensity of about 10) can be detected simultaneously by one photodetector 11 through a lens 10. In addition, in this case, as shown in FIG. 5, when the number of each laser element LDn (n=1, 2, 3,...) in the semiconductor laser array 9 is large, or when the interval between each laser element LDn is large. Since the configuration shown in FIG. 4 requires a photodetector 11 with a large light-receiving area, the monitor output light from each laser element LDn is connected to the photodetector 11 using an optical fiber cable 12. By intensively transmitting the light, it is possible to reduce the light receiving area.

Further, FIG. 6 shows the present invention for controlling the drive of each laser element based on the detection signal of the monitor output light b1, b2, b3 from each laser element LD1, LD2, LD3 by the photodetector 11. This shows an example of a configuration for concretely implementing the laser drive control method according to the present invention. Sample-and-hold circuits 141 to 143 sample and hold the detection signal, and each sample-and-hold output is compared with a preset reference voltage value Vs, and the sample-and-hold circuits 141 to 143 are provided corresponding to each laser element LD1 to LD3 until the two match. The comparators 151 to 153 provide commands to increase and decrease the laser drive current to the laser drive circuits 171 to 173, respectively. In addition, 161 to 16 in the figure
Reference numeral 3 indicates a low-pass filter that removes frequency components higher than the sampling frequency from the output signals of the comparators 151 to 153, respectively.

The operation for specifically implementing the laser drive control method according to the present invention in the apparatus configured as described above will be described below with reference to the time chart of FIG. 7.

First, as shown in FIGS. 7a, b, and c, each of the laser elements LD1 to LD is
3 to test laser beams B11, B21, B3
1 are fired in chronological order at regular intervals. In addition, T2 in the same figure indicates laser beams B12 and B in which the image information BS1, BS2, and BS3 on the n-th line, n+1-th line, and n+2-th line given from the outside are applied by optical modulation, respectively.
22 and B32 indicate an unblanking period during which optical recording is performed on the photosensitive drum. Next, each of the monitor lights b1, b2, and b3 from each of the laser elements LD1 to LD3 is detected by the photodetector 11 according to the intensity of each of the monitor lights. Figure 7d
indicates a voltage signal when the detection output of the photodetector 11 is amplified by the amplifier 13. In this case, the voltage value corresponding to the monitor light b1 is v1, the voltage value corresponding to the monitor light b2 is v2, The voltage value corresponding to the monitor light b3 is expressed as v3. Next, when the output of the amplifier 13 is sent to the sample-and-hold circuits 141 to 143, the amplifier outputs are sequentially synchronized with the rise of the laser beams B11 to B31 emitted from each laser element LD1 to LD3 during the blanking period T1. The voltage values v1, v2, and v3 are sampled and held in each sample-and-hold circuit 141-143. Note that FIG. 7 e, f, and g show the timings of the sampling pulses given to each of the sample and hold circuits 141 to 143, and at each timing, each voltage value v1 is changed as shown in h, i, and j of the same figure. ~v3 will be held respectively. Next, the output voltage of each sample-and-hold circuit 141 to 143 is output to a comparator 151.
~153, where the reference voltage Vs
The difference outputs are passed through low pass filters 161 to 163 and sent to laser drive circuits 171 to 163, respectively.
Sent to 173. Finally, each of the laser drive circuits 171 to 173 is connected to a low pass filter 16.
The drive current supplied to the laser elements LD1 to LD3 is increased or decreased as appropriate depending on the voltage level sent from the comparators 1 to 163 until the output of each comparator 151 to 153 becomes zero.
is controlled so that its output is always maintained at a predetermined value. At that time, for example, when the output voltage v1 of the sample-and-hold circuit 141 is equal to the reference voltage Vs, the output of the comparator 151 becomes zero and the drive current of the laser element LD1 is held at the previous value.
Furthermore, when the output voltage v2 of the sample-and-hold circuit 142 is smaller than the reference voltage Vs, the drive current of the laser element LD2 is controlled to be increased by the output Vs-v2 (becomes a positive value) of the comparator 152. , furthermore, when the output voltage v3 of the sample-and-hold circuit 143 is larger, the output v2-Vs of the comparator 153 (becomes a negative value)
Accordingly, control is performed in the direction of decreasing the drive current of the laser element LD3.

Further, FIG. 8 shows an example of a configuration for concretely implementing another laser drive control method according to the present invention, which will be described in detail below.

First, in this embodiment, each laser element LD1 to LD3 of a semiconductor laser array in a laser printer is arranged diagonally with respect to the main scanning X direction, as shown in FIG. The premise is that there is one photodetector 18 for synchronous detection (photodetector 18 in FIG. Vessel 7
(equivalent to ). At that time, each laser beam B1-B2 is sequentially scanned by the photodetector with a time difference Δt, so that each laser beam B1-B2 is detected by the photodetector in time series. Ru.

In addition, in the configuration shown in Fig. 8, each laser element
Laser beams B1 to B3 emitted from LD1 to LD3
an amplifier 19 that amplifies the output signal of the photodetector 18 that detects the photodetector 18 in time series, and a peak hold circuit 20 that holds the peak value of the amplified photodetection signal in response to a reset command RESET appropriately given from the outside. , a comparator 21 that compares its peak hold output with a preset reference voltage Vs.
and gate-on command GON1~ which is given the difference output from the outside with appropriate timing.
The gate circuits 221 to 223 selectively pass the GON3, hold each gate output for a certain period of time, and send the held outputs to the laser drive circuits 251 to 253 to the comparator 2.
Each laser element LD1~LD so that the difference of 1 becomes zero
3, and hold circuits 231 to 232 that give commands to increase or decrease the drive current. In addition, 241 to 243 in the figure are each hold circuit 231.
-232 show low-pass filters that remove frequency components higher than the sampling frequency from the output signals.

The operation for concretely implementing the laser drive control method according to the present invention in the apparatus configured as described above will be explained below with reference to the time chart of FIG. 9.

9a, b, and c show the synchronization signals of the main scanning lines corresponding to the laser elements LD1 to LD3, and each synchronization signal is sequentially detected by the photodetector 18 at a predetermined time. The drive control of each of the laser elements LD1 to LD3 is performed in advance to emit laser beams B1 to B3. Each laser beam B1
-B3 are detected in time series by the photodetector 18 according to their respective light intensities, and the detection output is sent to the amplifier 19 and amplified to a predetermined value. FIG. 9d shows the output signal of the amplifier 19, in which B1',
B2' and B3' indicate respective detection signals corresponding to the laser beams B1, B2, and B3, respectively;
Here, the light intensity of each laser beam B1 to B3 is B2<
It is assumed that B1<B3. In addition, FIG. 9 e, f, and g are based on the synchronization signal of each main scanning line detected by the photodetector 18, and the drive circuits 251 to 251 for each of the laser elements LD1 to LD3 after _t1 from the time of synchronization detection. It shows optical information signals output from each of the laser elements LD1 to LD3, which are modulated according to the image information BS1 to BS3 of the n-th line, n+1-th line, and n+2-th line sent to 253, respectively. . In this way, by appropriately timing the modulation in each laser element LD1 to LD3 according to the synchronization detection by the photodetector 18, even if the laser elements LD1 to LD3 are arranged diagonally, it is possible to prevent misalignment in the sub-scanning direction. It becomes possible to perform optical recording of multiple lines at the same time.

Next, the output of the amplifier 19 is sent to the peak hold circuit 20, where it receives a reset command given from the outside at the timing shown in FIG. 9h.
The peak values of each input V _B1 ′, V _B2 ′, and V _B3 ′ (corresponding to the voltage values of each laser light detection signal B1 ′, B2 ′, and B3′, respectively) are time-divided during each reset period according to RESET. hold it (see i in the same figure),
The hold output is sent to the comparator 21, where the reference voltage Vs is set according to the optimum laser output.
A comparison is made with When the difference output of the comparator 21 (see m in the same figure, treated here as V _B1 '=Vs) is sent to each gate circuit 221 to 223, the 9th A gate-on command is issued at each time point from T1 to T3 with the timing shown in Figures j, k, and l.
GON1 to GON3 (signals whose waveforms have been shaped by delaying each line synchronization signal of a, b, and c in the same figure by a predetermined time) are given, and the gate circuit 221 receives the signals from the comparator 21 during the period T1-2. Only the incoming zero-voltage signal (V _B1 '-Vs) is passed through, and the zero-voltage value is held in the hold circuit 231 (see n in the same figure), and then the gate circuit 222 performs a comparison during the period T2-T3. Only the negative voltage signal (V _B2 '-Vs) sent from the gate circuit 21 is passed through, and the negative voltage value is held in the hold circuit 232 (see o in the same figure).Furthermore, after T3, the gate circuit 2
23 passes only the positive voltage signal (V _B3 '-Vs) portion sent from the comparator 21 and causes the hold circuit 233 to hold the positive voltage value (see FIG.
(see p.). In addition, each hold circuit 231 to 233
The hold voltages at are each held for one mirror scan period.

Finally, the outputs of the hold circuits 231-233 are sent through low-pass filters 241-243 to the corresponding laser drive circuits 251-253, where they are supplied to the laser elements LD1-LD3 according to each voltage level of the hold output. The drive current is appropriately increased or decreased until the differential output of the comparator 21 becomes completely zero during one mirror scanning period, thereby controlling each laser light output so that it is always maintained at a predetermined value. At this time, since the output of the hold circuit 231 is zero, the laser drive circuit 251
The drive current of LD1 is maintained at its previous value without any increase or decrease, and the laser drive circuit 252 increases the drive current of laser element LD2 according to the differential voltage V _B2 '-Vs. The drive current of the laser element LD3 is reduced in accordance with the differential voltage V _B3 '-Vs.

Effects As described above, the laser drive control method according to the present invention uses a photodetector having a light-receiving area that allows simultaneous incidence of laser light emitted from each laser element of a semiconductor laser array used as a light source of a laser printer. The laser beams sequentially emitted from each laser element at regular intervals are detected in time series by the photodetector, and each laser element is detected according to the output level of each detected laser beam. Since the comparison control with the reference value is performed on a time-division basis so that the output of each laser element is always constant, the output of each laser element is It has the excellent advantage that stabilization can be achieved commonly and effectively, and as a result, good optical recording without exposure unevenness can be performed.

[Brief explanation of drawings]

Figure 1 is a perspective view showing an example of the basic configuration of a general laser printer, Figure 2a is a diagram showing a state in which each laser element of a semiconductor laser array is vertically arranged, and Figure 2b is a diagram showing each laser element at that time. FIG. 3a is a diagram showing the main scanning state of the laser beams, and FIG. And Figure 5 shows the monitor light emitted from each laser element.
FIG. 6 is a block diagram showing a configuration example for concretely implementing the laser drive control method according to the present invention, and FIG. 7 is a configuration example of the same. FIG. 8 is a block diagram showing a configuration example for concretely implementing another laser drive control method according to the present invention, and FIG. 9 is a time chart of various signals in the same configuration example. . 9... Semiconductor laser array, 10... Lens,
11...Photodetector, 12...Photofiber cable, 141-143...Sample and hold circuit, 151-153...Comparator, 161-16
3...Low pass filter, 171-173...Laser drive circuit, 18...Photodetector, 20...Peak hold circuit, 21...Comparator, 221-22
3...Gate circuit, 231-233...Hold circuit, 241-243...Low pass filter, 2
51-253...Laser drive circuit, LD1-LD3
...Laser element.

Claims (1)

[Claims] 1. In a laser printer configured to have a plurality of semiconductor laser elements arranged in an array in the sub-scanning direction to simultaneously perform optical recording of a plurality of lines in the main-scanning direction, each semiconductor laser element Using a photodetector that has a light-receiving area that allows the laser beams emitted from each to enter, the photodetector detects the laser beams emitted sequentially from each semiconductor laser element at fixed time intervals. Detected in chronological order,
The detection level of each laser beam outputted in time series from the photodetector is compared with a preset reference level, and each semiconductor laser element is set so that the detection level of each laser beam is equal to the reference level. A laser drive control method that performs drive control. 2. In a laser printer configured to simultaneously perform optical recording of multiple lines in the main scanning direction by providing a plurality of semiconductor laser elements in an array diagonally in the sub-scanning direction, The laser beams emitted from each semiconductor laser element are detected by the photodetectors in time series using photodetectors each having a light-receiving area that allows the emitted laser beams to enter. The detection level of each laser beam output in time series from the photodetector is compared with a preset reference level, and the detection level of each semiconductor laser element is adjusted so that the detection level of each laser beam is equal to the reference level. A laser drive control method that performs drive control.