JPH0976559A - Multi-beam type optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of ghost in a multi-beam type optical scanner and to improve the printing quality by providing a controller for giving print data stored at each beam to a beam driver corresponding to the beam at the timing decided by a detection signal. SOLUTION: LD drivers 5a, 5b emit beams for one scanning from laser diodes LD1, LD2 at the given timing. When parallel print data are read from a buffer A3, new next print data is written in a buffer B4 from a serial-parallel converter 2. When the data written in the memory of the buffer B2 is read, new print data is written in the buffer A3. The controls of alternately writing and reading in the buffers A3 and B4 are conducted by a controller 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used for a laser printer, a digital copying machine, etc. The present invention relates to a scanning device.

[0002]

2. Description of the Related Art Conventionally, an optical scanning device (laser scanner) used in a laser printer scans a recording member such as a photosensitive drum using a single beam.
A polygon mirror (rotating polygon mirror) that rotates at high speed is used as a beam scanning means. Further, in recent years, since the optical scanning device is required to have high speed, high resolution, color, and high quality, a multi-laser scanner that optically scans a plurality of beams simultaneously to form an image has been proposed. .

FIG. 16 shows a structural example of an optical unit of a conventional multi-beam laser scanner. Here, a laser printer that forms an image on the photosensitive drum 106 is shown. LD1 and LD2 (101) are laser diodes (hereinafter also referred to as LD) serving as a light source, and two beams are simultaneously emitted to the polygon mirror 102. The polygon mirror 102 is a mirror that rotates several thousands of times per minute, and is a mirror for swinging the beams emitted from the LD1 and LD2 in the vertical direction of the paper surface. The Fθ lens is a correction lens for correcting the laser scanning speed on the photosensitive drum surface 106 so as to be constant.

The mirror 104 is generally fixed and is a mirror for reflecting the beam toward the photosensitive drum. The BD detection unit 105 is a sensor (photodiode) that detects a reference position for printing and writing. LD1 and L
The beam emitted from D2 is polarized by the polygon mirror 102 and passes through the Fθ lens. Furthermore, the mirror 104
An image is formed on the photosensitive drum by being scanned by the surface reflected by the photosensitive drum 106.

FIG. 17 is an explanatory view of the beam scanning order. FIG. 17A shows a scanning beam (single beam) having only one light source.
The beams are scanned one by one in the order of 2 and a3. FIG.
16B shows a scanning beam (multi-beam) having two light sources shown in FIG. 16, and b11 and b12 are simultaneously scanned, and then b21 and b22 are simultaneously scanned.
Further, operations such as emission / stop of the beams from the LD1 and LD2, rotation control of the polygon mirror 102, and scanning position detection and control by the BD detection unit 105 are controlled by a controller (not shown).

FIG. 18 shows an example of the structure of a conventional light source for generating multiple beams. In the light source 110, two beam generating sources 111 corresponding to the laser diodes LD1 and LD2 of FIG. 16 are fixed to flanges 112 insulated from each other, and further, the flanges are opened at a predetermined interval to make an aluminum block housing. It is fixed to 113 by screwing.

Each flange is covered with an insulating film such as alumite. FIG. 19 shows a schematic block diagram of a driving portion of a conventional laser diode (LD). The controller 121 includes a laser diode LD1 and
The print signals A and B for driving the LD 2 (123, 125) are generated. The print signals A and B are pulse signals, respectively, which are LD drive circuits A and B (122, 1).
24). FIG. 20 shows a circuit example of the conventional LD drive circuits A and B shown in FIG. Here, when the print signal A or B is input to the transistors TR101 and TR102 as a pulse signal, a drive current flows through LD1 or LD2, and beam 1 or beam 2 is output.

[0008]

However, in the conventional light source shown in FIG. 18, although LD1 and LD2 are electrically insulated, since each flange is covered with an insulating film, the space between the flanges is large. There is a capacitor capacity (stray capacity). For example, as shown in FIG. 20, when the stray capacitance C exists and the driving current of the LD1 flows at the p point, it affects the driving current of the other LD2 at the q point.

FIG. 21 shows an explanatory view of this effect. When a drive pulse is generated at point p in FIG. 20 and the drive pulse rises at point q in FIG. 20 at the same time, the overshoot of the rising edge of the pulse at point q affects the pulse waveform at point p. Exert. This effect becomes noise and causes ghosts in the image output by beam 1. Similarly, the rising of the drive waveform of LD1 may affect the drive waveform of LD2, and in any case, it becomes a factor of deterioration of print quality.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to prevent ghosts from occurring in a multi-beam type optical scanning device and improve printing quality. Another object of the present invention is to provide a multi-beam type optical scanning device at a low cost while utilizing the controller used in the conventional single-beam type optical scanning device.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to a plurality of beam generating sources for generating a plurality of beams, a plurality of beam driving units for applying drive signals to the beam generating sources for generating the beams, and scanning of the beams. Each beam is detected at the reference position to start the, and a reference position detection unit that generates a detection signal corresponding to each beam, and a synchronization clock that is a reference based on the detection signal generated by the reference position detection unit The print data generation unit that generates print data, the print data storage unit that separates and stores the print data output from the print data generation unit for each beam, and the print data stored for each beam And a control unit for giving a beam drive unit corresponding to the above at a timing determined by the detection signal to provide a multi-beam type optical scanning device. A.

Further, according to the present invention, the reference position detecting section is composed of a single photo sensor, and a detection signal for separating a detection signal corresponding to each beam from a plurality of detection signals detected by the single photo sensor. You may further provide a separation part. Further, a detection signal delay unit for correcting a relative time interval shift between the detection signals for each beam separated by the detection signal separation unit so as to match a predetermined reference interval may be further provided.

Further, the plurality of beam generating sources may each be constituted by a laser diode, and each laser diode may be connected to a common ground terminal as a multi-beam type optical scanning device, and each laser diode may be common. It may be a multi-beam type optical scanning device connected to the power supply terminal.

Further, according to the present invention, the beam driving section includes a subtracting section for subtracting two signals, and an edge signal generating section for detecting a rising edge of the given print data and generating an edge signal. The subtraction unit of the arbitrary beam drive unit A performs the subtraction between the print data given to the beam drive unit A and the edge signal generated by the edge signal generation unit of the other arbitrary beam drive unit B to perform beam drive. The present invention provides a multi-beam type optical scanning device for generating a drive signal for generating a beam corresponding to the section A.

Here, the beam generation source may be any one that can generate a laser beam, and for example, a laser diode can be used. In addition to this, a gas laser may be used. The beam driver is a circuit for driving a laser diode that generates a beam,
It is composed of switching elements such as transistors.
The reference position detector is a so-called photodetector, and it is preferable to use a photodiode for its performance. Further, it is preferable to use one photodiode because of its structure.

By irradiating the photodiode with a beam, a detection signal is output from the photodiode. Since the beam is scanned by the rotating mirror, the detection signal is output as a pulse signal. Generally, this detection signal is referred to as a BD signal (Beam, Det).
ect), and the reference position detection unit is also referred to as a BD detection unit. The BD signal is generated each time each beam is applied to the photodiode. Since each beam emits light at a predetermined timing, it is output as a discrete and continuous pulse signal.

The detection signal separating section is for separating the BD signal corresponding to each beam from the continuous pulse signal, and is configured as a BD signal separating circuit in which a timer and a logic element are combined. The print data generator may be the one used in the conventional single-beam type optical scanning device. Hereinafter, the print data generation unit will be referred to as a controller.

A RAM or the like is used as the print data storage unit 12, but it is preferable that the print data storage unit 12 is divided into two buffers (A, B) in order to speed up printing. Each buffer (A, B) is preferably divided into a memory area for storing print data for generating each beam for each beam. Then, the print data corresponding to the first beam is alternately written into the memory regions for the first beam in the buffers A and B by the control unit and is read out alternately. Further, since the print data given from the controller is generally serial data, it is preferable to convert it into parallel data by a serial-parallel conversion circuit before storing it.

The control unit is a memory control unit for controlling reading and writing of the buffers A and B, and can generally be constituted by a logic circuit such as a counter. The detection signal delay unit uses a delay element such as an LC integration circuit and is configured by a delay circuit that changes the output timing of the detection signal. The subtraction unit can be easily configured by combining a logic element such as an operational amplifier, and the edge signal generation unit can be configured by a delay element.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. The present invention is not limited to this. FIG. 1 is a block diagram of a laser diode driving portion of a multi-beam type optical scanning device according to the present invention. Here, an embodiment using two laser diodes is shown.

In FIG. 1, controller 1, LD driver circuits (5a, 5b), LD1 (6a), LD2 (6)
The a) and BD detection unit 7 may be the same as those used in the related art shown in FIGS. 16 and 19 and the like. As the controller 1, it is assumed that the same controller as in the case where optical scanning is performed using a single beam is used. Therefore, the controller 1 outputs a continuous serial video signal (hereinafter also referred to as a print signal) used when performing optical scanning with a single beam, together with the synchronization clock signal.

In this embodiment, by the following specific building blocks, the serial data for a single beam is converted into parallel data for generating two beams, and two beams are emitted at a predetermined timing. The feature is that two laser diodes are driven.
The serial-parallel conversion circuit 2 is a circuit that converts a serial print signal sent from the controller 1 into parallel data.

The buffer A (3) and the buffer B (4) are
It is a memory for storing the converted parallel data, and a RAM is usually used. The memory 1 of the buffer A (3) and the memory 1 of the buffer B (4) store parallel data for the LD1 (6a).
Memory 2 and buffer B (4) memory 2 are LD2
The parallel data for (6b) is stored. For example, memory 1 of buffer A (3) and buffer B
By alternately reading the data in the memory 1 of (4), a drive signal for emitting a beam from the LD 1 (6a) is created. The details will be described later.

The LD drive circuits 5a and 5b are for causing the laser diodes LD1 (6a) and LD2 (6b) to emit light. For this, a circuit similar to the conventional one can be used, but a plurality of lasers are used. In order to prevent a ghost at the time of printing which is generated by simultaneously driving the diodes, it is preferable to have a circuit configuration described later. Reference numerals 13a, 13b, 14a and 14b in the figure are OR circuits.
As the BD detection unit 7, one photodiode is used as in the conventional case.

The BD signal separation circuit 8 converts the plurality of BD signals obtained by the BD detection unit 7 into B signals for each laser diode.
It is to be separated into D signals (BD1, BD2). BD
If the detector 7 is separately provided for each laser diode, it is not necessary to provide such a separation circuit, but it is difficult to provide a plurality of BD detectors because of the configuration of the optical scanning device, and position adjustment is performed. Advanced maintenance is required, which leads to cost increase. Therefore, as will be described later, B
Since the D signal separation circuit 8 can be easily configured by a timer and several logic elements, one B
The D detection unit 7 and the BD signal separation circuit 8 will be used. As a result, a simple circuit configuration can be used for BD signal detection and separation.

The delay circuits 11a and 11b are separated from each other by B.
This is a circuit that corrects the timing deviation of the D signals (BD1, BD2). The BD signals BD1 and BD2 have a timing shift due to a light source mounting error and a laser diode power difference.
The print dots are displaced, and the print quality is deteriorated.
Therefore, it is necessary to correct the timing shift by the delay circuits 11a and 11b. BD1 'and BD2' are BD signals after this correction.

The pseudo BD generation circuit 9 generates a pseudo BD signal which serves as a reference for the timing of the print signal output by the controller 1. When two beams are used, the writing speed is halved, so the BD signal separated by the BD separation circuit 8 appears in a cycle twice as long as the cycle of emitting each beam. Therefore, since the separated BD signal cannot be given to the controller 1 as it is, the pseudo BD signal is generated at a timing of 1/2 cycle of the BD signal and given to the controller 1. The generation circuit 9.

Further, in general, when scanning is performed using n beams, the pseudo BD generation circuit 9 uses the separated BDs.
It is configured to generate a pseudo BD signal with a period equal to the number of beams divided by n. This pseudo BD generation circuit 9
Can be realized, for example, by combining circuit elements such as a counter.

The memory control circuit 10 is a circuit for controlling reading and writing of the memories of the buffer A (3) and the buffer B (4). Where, for example,
When generating a drive signal for LD1 (6a),
When the memory 1 of the buffer A (3) is at the write timing, the memory control circuit 10 is at the read timing of the memory 1 of the buffer B (4).
When the memory 1 of is at the read timing, the memory of the buffer B (4) is at the write timing,
Control each memory.

The memory control circuit 10 is realized by a circuit element such as a counter, for example. The memory control circuit 10 and each memory in the buffer are connected by chip select (CS), read / write (R / W), and control signal lines of address lines. The laser emission timing generation circuits 12a and 12b are delay circuits 11a and 11
The timing signals (VD01, VD02) for emitting a beam are created based on the BD signal output from b, and can be realized by circuit elements such as a counter and a gate.

The interval between one BD signal and the next BD signal is
Since one scanning period in the horizontal direction is shown, the timing signal is output for a predetermined time within the period of a certain BD signal and the next BD signal. For example, one horizontal scanning period is 6
At 40 μsec, the timing signal is 100 μse
About c is output. Further, the timing signal (V
D01, VD02) are input to the OR circuits 14a, 14b to generate drive signals for the respective laser diodes.

Next, the outline of the operation of the laser diode driving portion of the present invention will be described with reference to FIGS. 1 and 4. Here, an example in which scanning is performed by two beams will be shown. FIG. 4 shows an embodiment of a read / write time chart for the memory in the buffer of the present invention. First, the print signal synchronized with the synchronization clock is sent from the controller 1 to the serial-parallel conversion circuit 2. The synchronous clock used at this time is a pseudo BD signal generated by the pseudo BD generating circuit 9, and is a signal indicating the start of scanning for each laser diode. As described above, in FIG. 4, the BD signal BD1 ′ input to the pseudo BD generation circuit 9 appears in a cycle that is twice the cycle in which two beams are emitted. Therefore, in the pseudo BD generation circuit 9, BD
BD of FIG. 4 at the timing of ½ of the cycle of 1 ′
A pulse signal corresponding to 1 ″ is produced and given to the controller 1 as a pseudo BD signal as shown in FIG.

The controller 1 adopts this pseudo BD signal as a synchronizing clock and synchronizes with the print signal (w
1 to w4) are transmitted. The serial-parallel conversion circuit 2 takes in a serial print signal for each laser diode with the synchronous clock as a reference, and outputs it to the memory of the buffer A (3) as parallel data for each 8-bit, for example.

Two laser diodes (LD1, LD
When 2) is used, the parallel print data (w1) for the laser diode LD1 is written in the memory 1, and the parallel print data (w2) for the laser diode LD2 is written.
Are written in the memory 2. The memory control circuit 10 controls the writing of data from the serial-parallel conversion circuit 2 to the buffer A (3) using a read / write line, a chip select line, and an address line.

After the parallel print data (w1, w2) has been written in the memories 1 and 2 of the buffer A for one scan, the memory control circuit 10 reads them (r1, r2). Further, the read data (r1, r2) is used as the laser emission timing generation circuit 1
At the timing created by 2a and 12b, the OR circuit 14
It is output to the LD drive circuits 5a and 5b through a and 14b.

After that, the LD drive circuits 5a and 5b have laser diodes LD1 and LD2 at given timings.
To emit a beam for one scan. Also, buffer A
When reading parallel print data from (3) (r
1, r2), new new print data (w3, w4) is written from the serial-parallel conversion circuit 2 to the buffer B (4). When the print data written in the memory of the buffer B (4) is read out, the buffer A
New print data is written in (3). The memory control circuit 10 controls the writing and reading alternately to and from the buffer A (3) and the buffer B (4).

As described above, since two sets of buffers A and B are provided to alternately read and write the print data, it is possible to stabilize high-speed printing performed by driving two laser diodes. Is. Further, by adopting the configuration as shown in FIG. 1, the controller 1, the LD drive circuits 5a, 5b, and the BD detection unit 7 can be the same as those of the single beam type optical scanning device which has been conventionally used. Further, the transmission control of the print data in the controller 1 does not need to be the control peculiar to the multi-beam type,
Since the control similar to that of the conventional single beam type may be performed, the load on the controller does not increase.

Embodiments of the serial-parallel conversion circuit 2, the LD drive circuits 5a and 5b, the BD separation circuit 8 and the delay circuits 11a and 11b, which are the structural features of the multi-beam type optical scanning device of the present invention, will be described below. Will be described.

Embodiment 1 FIG. 2 shows an embodiment of a serial-parallel conversion circuit. Where register Reg 1 and
Reg 2 (21, 22) is for converting serial data into parallel data. MEM23 is the buffer A
Or, it is a memory in B and stores the converted parallel data. Reference numeral 24 is an inverting circuit, and 25 is a frequency dividing circuit. The frequency divider circuit 25 doubles the cycle of the synchronous clock given from the controller 1.

The MEM 23 is connected to the memory control circuit 10 of FIG. 1 by an R / W line, a CS (chip select) line and an address line, as in the normal memory control. The registers Reg 1 and Reg 2 and the MEM 23 are connected by, for example, an 8-bit bus line.

FIG. 3 shows a time chart of this serial-parallel conversion circuit. The print data is 1-bit serial-parallel data and is input to the register Reg 1 (21) or Reg 2 (22) in synchronization with the synchronous clock. Here, if high-speed and high-resolution printing is required, in order to write serial data in the register, 1
A very high-speed synchronous clock of 0 and several ns is required.

Therefore, the frequency divider circuit 25 causes the video clock (CL) having a cycle twice that of the synchronous clock (CLK).
K × 2) is generated, and the print data is Reg 1 (21) and R at the rising and falling timings of this video clock.
It should be taken alternately into eg 2 (22). For example,
The print data "1" in FIG. 3 is taken into Reg 1 at the rising edge of the video clock, and the print data "2" is taken into Reg 2 at the falling edge of the video clock.

Further, the print data alternately fetched into Reg 1 and Reg 2 is written into the MEM 23 when the memory control circuit outputs a write signal. In this way, by serially fetching the serial print data in the registers (Reg 1, Reg 2) and writing them as parallel data in the memory MEM 23, high speed and high resolution printing can be supported. Further, by adopting the configuration as described above, it is possible to use the high-speed synchronous clock as it is, prevent the synchronization deviation due to the delay of the circuit element that may occur when converting to the parallel data, and stabilize the print data. Can be captured.

Example 2 Here, a multi-beam type L is used.
An example of the D drive circuits 5a and 5b will be described. FIG.
FIG. 7 shows a schematic block diagram of a laser diode driving portion in one embodiment of the present invention. Here, it is assumed that two laser diodes (LD1 and LD2) that generate a beam are used. The light source is an LD as shown in FIG.
It is assumed that the LD 1 and LD 2 are attached to flanges, respectively, and the flanges are covered with an insulating film and fixed to a block housing made of aluminum at a predetermined interval.

In FIG. 5, the LD1 drive section 41 receives the print signal A given from the controller and generates a signal for driving the laser diode LD1. Similarly, the LD2 drive unit 42 receives the print signal B as an input,
A signal for driving the laser diode LD2 is generated. L
The D1 driving unit 41 and the LD2 driving unit 42 include an edge signal generating unit (43a, 43b) and a subtracting unit (44a, 44b) in order to remove noise components that affect each other. The edge signal generators (43a, 43b) detect the rising edge of the print signal and generate a pulse signal indicating the rising edge, and this pulse signal is input to the other subtracting section. The pulse signal input to the other subtraction unit is used to cancel the noise component as shown in FIG.

FIG. 6 shows a schematic diagram of the signal waveform of each part of FIG. In FIG. 6, since the capacitor capacitance is formed between the flanges as shown in the conventional example, the print signal A has a noise component n1 in the LD drive section 41, and has a drive waveform c. On the other hand, the edge signal generator 43b detects the rising edge of the print signal B and generates the edge signal waveform f as shown in the figure. The subtraction unit 44a subtracts the edge signal waveform f from the drive waveform c to obtain the LD
1 Drive waveform g is generated. In this way, a noise-free drive waveform is obtained as the drive waveform for the LD1, and as a result, it is possible to prevent the occurrence of ghosts.

Similarly, the noise component n2 is added to the print signal B.
Is generated, the noise component is removed from the drive waveform e with noise in the subtractor 44b by using the edge signal waveform d generated by the edge signal generator 43a.
As described above, by providing the edge signal generating section and the subtracting section in the respective laser diode driving sections of LD1 and LD2, it is possible to remove the noise components which are generated by the capacitor capacitance formed in the configuration and which affect each other. it can.

FIG. 7 shows the laser diode (L
The detailed structural example in one Example of the drive part of D) is shown. Here, LD1 and LD2 are laser diodes, and PD1 and PD2 are diodes that control the current flowing through the laser diodes. TR1 and TR2 are np for controlling the current flowing through LD1 by the print signal A or B.
It is an n-type transistor. The amplifier 51 and the power control unit 52 are for keeping the emission intensity of the laser constant.

The NOT circuit 53, the delay circuit 54, the AND circuit 55, and the transistors TR2 and TR4 detect the rising of the print signal to generate a pulse signal, and the edge signal generators (43a, 43b) described above. Equivalent to. The collector terminals of TR2 and TR4 are connected to the emitter terminals of TR1 and TR3 via resistors R10 and R5, respectively. In this way, TR1 and TR4,
The subtraction unit (44a, 44b) described above is configured by connecting TR2 and TR3.

The resistance values of the resistors R1 to R10 are, for example, R1, R6 = 5 to 30Ω, R2, R7 = 1.
00 to 1KΩ, R3, R8 = 100Ω, R4, R9 = 1
00Ω, R5, R10 = 10 to 100Ω can be used. The power supply voltage V supplied to the LD1 and LD2 is preferably in the range of +5 to + 24V, and can be set to + 24V, for example.

Points c, d, e, f, g, and h in FIG. 5 correspond to points c, d, e, f, g, and h in FIG. 7, and the signal waveform at each point is shown in FIG. It becomes a thing.
That is, even if the noise n1 occurs in the drive signal waveform at the point c, the edge signal waveform f is added to TR1, so that the laser diode LD1 has a waveform of g (= cf) in which the noise n1 is canceled. A pulse is applied.

Similarly, even if the noise n2 is generated in the drive signal waveform at the point e, the edge signal waveform d is added to TR2. Therefore, the noise n appears in the laser diode LD2.
A pulse having a waveform of h (= ed) in which 2 is canceled is applied. Therefore, since the drive signal corresponding to the print signals A and B and containing no noise component is applied to the LD1 and LD2, it is possible to prevent the occurrence of ghost in printing.

In the embodiment shown in FIG. 7, LD1 and PD1,
Also, a configuration of a type in which the power supply terminal (+ V) of LD2 and PD2 is common is shown. In addition to this, as shown in FIG.
Ground terminals (GN) of LD1 and PD1, and LD2 and PD2
A configuration of the type common to D) may be used.

FIG. 8 shows another embodiment of the circuit near LD1 and LD2 in FIG.
In order to drive D1 and PD2, a negative power source (-V
= −50V to −24V), and transistors TR1 and TR2 for driving LD1 and LD2.
And resistors R1 ′ and R3 ′ on the power supply terminal (+ V) side.

Also in the embodiment shown in FIG. 8, the pulses applied to LD1 and LD2 have the driving waveforms g and h shown in FIG. 6, and the noise component can be removed. Therefore, the print signals A and B are supplied to the drive unit of the laser diode.
Edge signal generator (4
3a, 43b) and the subtraction unit (44a, 4b) for canceling the noise component that affects the other by the edge signal generated by the edge signal generation unit at the rising edge of the pulse. A noise component can be removed from the laser diode drive signal to prevent the occurrence of ghosts during printing.

In order to remove the noise component as described above, coils (LD1, LD2) may be inserted between the power supply voltage + V and LD1 and LD2, respectively, as shown in FIG. With this coil (L1, L2),
It is possible to prevent a steep change in the drive waveform of the laser diode, and thus remove the noise component. In addition,
The inductor value of the coil may be about 10 μH, for example.

Further, as shown in FIG. 10A, by providing a plurality of transistors, it is possible to prevent a sharp change in the drive waveform of the laser diode. FIG. 10B shows a current waveform flowing through the three transistors TA, TB, TC shown in FIG. 10A and a current waveform flowing through the laser diode. Here, the timing of driving the laser diode by the three transistors TA, TB, and TC is divided into three stages so that the rising and falling of the waveform of the current flowing through the laser diode is gentle. This makes it possible to reduce the influence of a sharp change in the laser diode drive waveform on the other drive waveform. It should be noted that in order to make a drive timing shift as shown in FIG. 10B, three transistors TA, TB,
Of the TC characteristics, the current amplification factor (hfe) may be constant.

In the above, the embodiment in which the ghost is prevented by removing the noise component generated when the light source composed of the two beam generating sources is constituted by one aluminum block housing has been shown. It is also possible to remove the noise component by configuring the two beam generation sources as separate casings and fixing them on a plastic frame plate with a predetermined interval. FIG. 11 shows an embodiment in which the two beam generation sources are configured as separate block housings. FIG.
1, (a) is a plan view, (b) is a front view, and (c) is a side view. The two aluminum block cases in the figure
A flange incorporating a laser diode (LD1 or LD2) is attached.

The aluminum block casings 1 and 2 are frame plates each having a concave portion at a lower portion thereof, a convex portion B engaging with the concave portion, and a convex portion A stabilizing the aluminum block. It is attached. Here, the convex portion A has a trapezoidal shape when viewed from above so that the optical axis of the beam emitted from the laser diode forms a predetermined angle, and an aluminum block is fixed along the side surface of this trapezoidal shape. It is preferable to do so. Here, as the material of the frame plate, it is necessary to use a material that does not generate stray capacitance between the two aluminum blocks.

For this purpose, for example, as a frame,
It is preferable to use a material having no conductivity such as a plastic material. Further, as the material of the block casing for fixing the flange, it is most preferable to use aluminum in terms of molding, but a plastic material may be used. In this way, the two beam emission sources are separate block housings,
Further, by fixing this to a plastic frame, it is possible to suppress the noise component generated in the laser diode drive signal.

Embodiment 3 Next, an embodiment of the BD separation circuit 8 of the present invention will be described. In FIG. 12, the BD detection unit 7
An example of a BD separation circuit 8 that separates and extracts three BD signals (SIG5, SIG6, SIG7) from the BD signal (SIG1) given from As shown in the figure, this circuit has two timers 61 and 62 (TIMER1, T
It is easily configured by IMER2) and some logic elements.

FIG. 13 shows a time chart of BD signal separation. In this example, an optical scanning device having three laser diodes is considered. At this time, three BDs are detected by one BD detection unit, so that the BD detection unit 7 outputs BDs corresponding to the respective beams.
A signal is generated. Since the three beams have different timings with which the BD detection unit 7 is irradiated, BD signals generated by the respective beams are superimposed and output as pulse signals that are deviated in time. For example, in FIG. Signals (S1, S2, S3) such as SIG1.

The timers 61 and 62 are for generating the timing for separating each signal, and the set time of this timing is the mounting position and angle of the laser diode and the distance between other components. Should be determined by the conditions of. For example, SIG1
If the period from S1 to S2 in is about 15 μsec, the set time counted by the timers 61 and 62 is preferably about 20 μsec. here,
Re-trigger type timers 61 and 62 are used.

The time chart of FIG. 13 will be described below. First, the signal SIG input to the BD signal separation circuit 8
The timer 61 is started at the falling edge of the first BD signal (S1) of 1. At this time, the signal SIG2 is output from the timer 61.
Is output for a fixed time T. Here, the fixed time is a preset time, and is set to a time longer than the time when the next BD signal (S2) will come.

Since the timer 61 is also triggered by the following signals S2 and S3, the output of the timer 61 is S after the signal S1 is input as shown by SIG2 in FIG.
It is continuously output until after 3 is input. SIG3
Is a logical product of SIG1 and SIG2, and is obtained by removing the signal S1 from SIG1 as shown in the figure. The timer 62 is operated at the fall of SIG3. Since the timer 62 is also a re-trigger type, the output of the timer 62 is SIG4 in the figure.

Using the above SIG1 to SIG4, 3
Independent BD for each laser diode
The signals (S1, S2, S3) are taken out. That is, BD
SIG5 corresponding to the signal S3 can be taken out by the logical product of SIG3 and SIG4. In addition, the BD signal S2
SIG6 corresponding to SIG2, SIG3, and SIG
It can be obtained by ANDing with the negation of 4 and BD
SIG7 corresponding to the signal S3 is SIG1 and SIG2.
It can be taken out by the logical product with the negation of.

As described above, the BD signal detected by the plurality of beams is output as a pulse signal superposed from the BD detection section, but each of the beams can be easily converted by the BD signal separation circuit as shown in FIG. BD corresponding to
The signals can be separated. Further, also in the present invention using a plurality of beams, the BD detection unit 7 can be configured by one photodiode, so that it can have the same configuration as in the case of using a conventional single beam.

Therefore, the BD detection unit and the B
By providing the D signal separation circuit, the circuit configuration of the BD detection portion of the multi-beam type optical scanning device can be simplified. Although the example of the BD signal separation circuit in the case of using three laser beams has been shown above, the BD signal separation circuit can similarly be used in the case of using two or four or more laser beams in the same manner as the timer and the logic element. Can be configured by.

Fourth Embodiment Next, an embodiment of the delay circuits (11a, 11b) in the embodiment of FIG. 1 of the present invention will be described. Therefore, this is an example of a delay circuit in the case of an optical scanning device using two laser beams. According to the present invention, as described above, a plurality of beams are detected by one BD detection unit, and the BD for each superimposed beam is detected.
The signal is separated by the BD signal separation circuit. When two beams are used, two BD signals (BD1 and BD2) are superimposed and detected, but the two BD signals are detected as signals that are shifted by a predetermined time by the BD signal separation circuit. For example, as shown in FIG. 14, BD1 and B
D2 is detected a time interval T apart.

However, the time interval T actually detected is
Is often different from the time interval Ts scheduled at the time of design (see FIG. 14) due to a mounting position error of the BD detection unit in the optical scanning device of the present invention and a difference in beam power. The delay circuit shown below is for correcting such a timing shift of the BD signal.

FIG. 15 shows the delay circuit (11a, 11a,
11b) shows an example. In the figure, DELAY
Reference numerals 71 and 72 denote delay elements, which can be configured using, for example, an LC integrating circuit. The output signal of this DELAY is BD
1 ', BD2'. SR Flip Flock 73
The counter 74 generates the timing for counting, and is set by the input of BD1 ', BD2'
It is reset by the input of.

The counter CNT74 has BD1 'and BD
The time interval T with 2'is counted. The reference value setting circuit 76 uses a BD signal BD which is previously determined at the time of design.
A count value (reference value) corresponding to the time interval Ts between 1 and BD2 is generated. Comparator CMP75
Is to compare the actual count value of the time interval T by the counter CNT74 with the reference value of the time interval Ts at the time of design, and output the difference.

The output value of the comparator CMP75 is DE
It is fed back to the LAYs 71 and 72, and the output timings of the BD1 and BD2 are adjusted by DELAY based on this output value. For example, when the time interval T between BD1 and BD2 is narrower than the reference value, the DELAY 72 adjusts the timing at which BD2 is output slightly to the time interval Ts, and outputs it as BD2 ′. The BD1 'and BD2' correspond to the outputs of the delay circuits 11a and 11b in FIG.

As described above, since the delay circuit automatically corrects the timing deviation of the BD signal while comparing it with the reference value of the output timing of the BD signal, the printing caused by the timing deviation of the BD signal occurs. It is possible to prevent misalignment of dots. Further, since the automatic correction is performed by the feedback as described above, stable performance as the optical scanning device can be maintained even with environmental changes such as temperature changes.

The delay times of the DELAYs 71 and 72 may be adjusted by switching with a DIP switch. In this case, some setting time must be prepared at the time of design and set by the user before use, but there is an advantage that the circuit can be rationalized.

The configuration and function of the optical scanning device mainly using two beams as the multi-beam type optical scanning device of the present invention have been described above, but the same applies to an optical scanning device using three or more beams. By adopting the above configuration, it is possible to provide a multi-beam type optical scanning device that prevents the generation of noise that causes ghosts and that has stable performance even with environmental changes.

[0077]

According to the present invention, the print data is stored separately for each beam, and the print data is given to the beam drive section at a timing based on the detection signal detected by the reference position detection section. Therefore, it is possible to provide a multi-beam type optical scanning device capable of preventing the occurrence of ghost and improving the printing quality.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a laser diode (LD) driving portion of a multi-beam type optical scanning device according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram of an embodiment of a serial-parallel conversion circuit of the present invention.

FIG. 3 is a time chart of the serial-parallel conversion circuit of the present invention.

FIG. 4 is an embodiment of a time chart of reading and writing to the memory in the buffer of the present invention.

FIG. 5 is a schematic configuration block diagram of an LD drive portion in one embodiment of the present invention.

6 is an explanatory diagram of a drive signal waveform in each part of FIG.

FIG. 7 is a detailed configuration block diagram of an LD driving portion in an embodiment of the present invention.

8 is a configuration diagram of another embodiment of a portion near the LD in FIG.

9 is a configuration diagram of another embodiment of a portion near the LD in FIG.

10 is a configuration diagram of another embodiment of a portion near the LD in FIG.

FIG. 11 is an embodiment in the case where the two beam generation sources are configured as separate casings in the present invention.

FIG. 12 is a configuration block diagram of an embodiment of a BD separation circuit of the present invention.

FIG. 13 is a time chart of the separation operation of the BD separation circuit of the present invention.

FIG. 14 is an explanatory diagram of BD signal detection timing according to the present invention.

FIG. 15 is a configuration block diagram of an embodiment of a delay circuit of the present invention.

FIG. 16 is a configuration diagram of a conventional optical unit.

FIG. 17 is an explanatory diagram of scanning of a single beam and a multi beam.

FIG. 18 is a configuration diagram of a conventional light source that generates multiple beams.

FIG. 19 is a configuration block diagram of a conventional laser diode (LD) driving portion.

FIG. 20 is a configuration diagram of a conventional LD drive circuit (A, B).

FIG. 21 is an explanatory diagram of drive waveforms of a conventional LD.

[Explanation of symbols]

 1. Controller 2. Serial-parallel conversion circuit 3. Buffer A 4. Buffer B 5a. 5b. LD drive circuit 6a. , 6b. Laser diode 7. BD detector 8. BD separation circuit 9. Pseudo BD generation circuit 10. Memory control circuit 11a. , 11b. Delay circuit 12a. , 12b. Laser generation timing creation circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunji Kitagawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Yoshitaka Murakawa 1015, Kamedotachu, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor Tatsuya Itakura 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Yasuo Numata 1015, Kamikodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) Inventor, Ogawa Wajo Kanagawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Fukuoka Prefecture Fujitsu Limited (72) Inventor Fumiaki Seto 1015, Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (6)

[Claims] 1. A plurality of beam generating sources for generating a plurality of beams, a plurality of beam driving units for giving a driving signal for causing the beam generating sources to generate a beam, and a reference position for starting scanning of the beams. There is a reference position detector that detects each beam and generates a detection signal corresponding to each beam, and a print data generator that generates print data synchronized with a synchronization clock based on the detection signal generated by the reference position detector Unit, a print data storage unit that stores the print data output from the print data generation unit separately for each beam, and the print data stored for each beam to the beam drive unit corresponding to the beam. A multi-beam type optical scanning device comprising: a control unit that gives a timing determined by a detection signal. 2. The reference position detection unit is composed of a single photosensor, and further comprises a detection signal separation unit for separating a detection signal corresponding to each beam from a plurality of detection signals detected by the single photosensor. The multi-beam type optical scanning device according to claim 1, further comprising: 3. A detection signal delay unit that corrects a relative time interval shift between the detection signals for each beam separated by the detection signal separation unit so as to match a predetermined reference interval. The multi-beam type optical scanning device according to claim 2. 4. The multi-beam type optical scanning device according to claim 1, wherein each of the plurality of beam generation sources is composed of a laser diode, and each laser diode is connected to a common ground terminal. 5. The multi-beam type optical scanning device according to claim 1, wherein each of the plurality of beam generation sources is composed of a laser diode, and each laser diode is connected to a common power supply terminal. 6. The beam driving unit includes a subtracting unit that subtracts two signals, and an edge signal generating unit that detects a rising edge of given print data and generates an edge signal. The subtracting section of the section A is the beam driving section A
Is subtracted from the print data given to the beam driving unit B and the edge signal generated by the edge signal generating unit of any other beam driving unit B to generate a driving signal for generating a beam corresponding to the beam driving unit A. The multi-beam type optical scanning device according to any one of claims 1, 4 and 5.