JP2001281571A - Synchronizing signal generating device and optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a synchronizing signal from which the influence of external noise is eliminated regardless of the scanning speed of a light beam. SOLUTION: Photodiodes 44A and 44B are arranged so that the light beam successively passes the light receiving surfaces of the photodiodes 44A and 44B (see (A)), and output A from the photodiode 44A and output B from the photodiode 44B (see (B)) are respectively inputted into a comparator (see (C)). Then, a detection signal (see (D)) staying at a high level in a period when the signal level of the output A is higher than that of the output B is generated, a delay signal (see (E)) obtained by delaying the detection signal by a specified time is generated, and an SOS signal (see (F)) equivalent to the AND of the detection signal and the delay signal is obtained. The light beam is modulated by setting timing that the SOS signal transits from the high level to a low level as reference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronizing signal generating device and an optical scanning device, and more particularly, to an optical scanning device for deflecting a light beam so as to scan an object to be scanned, and a timing synchronized with the scanning of the light beam. The present invention relates to a synchronization signal generation device that generates a synchronization signal for performing a predetermined process.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus (for example, a copying machine, a printer,
Facsimile machine or these multifunction machines)
As an exposure device for exposing a charged photoconductor according to an image to be formed and forming an electrostatic latent image on the photoconductor,
Optical scanning in which a light beam emitted from a light source such as a laser diode (LD) is modulated according to an image to be formed, and the modulated light beam is deflected by a deflecting means such as a polygon mirror to scan on a photoconductor. The device is widely used.

In this type of optical scanning device, in order to modulate the light beam at a timing synchronized with the scanning of the light beam, the scanning start side end (SO
S) when the light beam is deflected in the direction corresponding to (S), the light sensor (SO
An S sensor is provided, and the SOS sensor outputs a synchronization signal in which a pulse-shaped signal level change (detection pulse) occurs each time a light beam is received. The modulation of the light beam in each scan of the light beam is started at a timing synchronized with the synchronization signal (specifically, after a lapse of a predetermined time after a detection pulse is generated in the synchronization signal).

[0004] As described above, since the synchronization signal is a signal that defines the modulation start timing in each scan of the light beam, extraneous noise is mixed during the period when the SOS sensor is not receiving the light beam. When a pulse-like change corresponding to external noise occurs in the signal level of the synchronization signal, the modulation start timing of the light beam is disturbed,
In some cases, unsightly noise is added to an image formed by the image forming apparatus, or a streak-like image quality defect occurs.

[0005] In order to solve the above-mentioned problem, Patent No. 28
No. 80120, when a synchronization detection signal (detection pulse) is output from a synchronization detector, a clock pulse of a constant frequency is counted by a counter to generate a mask signal according to the cycle of the synchronization signal, and the generated mask signal A technique is disclosed in which a gate is applied to the next detection pulse to prevent a malfunction due to noise in a period other than a period in which the detection pulse will be generated.

[0006]

However, in the above technique, once the gate timing is disturbed due to malfunction of the counter for generating the mask signal or the like, the disturbed timing does not return or even if the disturbed timing returns. There is a problem that an image formed during that time is disturbed. Further, in an optical scanning device capable of changing the scanning speed of the light beam to a plurality of speeds, if the scanning speed of the light beam is changed, the period of the synchronization signal also changes. It is necessary to change and set according to the scanning speed, and there is a problem that the device configuration becomes complicated. Furthermore, since the period of the synchronizing signal changes continuously while the scanning speed of the light beam is being increased or decreased, the gate operation needs to be stopped, and malfunction may occur if external noise is mixed during this period. There is.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a synchronizing signal generating apparatus capable of generating a synchronizing signal excluding the influence of external noise regardless of the scanning speed of a light beam. Is the purpose.

Another object of the present invention is to provide an optical scanning device capable of modulating a light beam at a fixed timing without being affected by external noise, regardless of the scanning speed of the light beam.

[0009]

According to a first aspect of the present invention, there is provided a synchronizing signal generating apparatus for converting a light beam deflected by a deflecting means so as to scan an object to be scanned. Detection at a specific position within the beam scanning range,
Detection signal generation means for generating a detection signal having a first signal level during a period in which the light beam passes through the specific position and a second signal level in other periods;
A delay unit configured to generate a delay signal in which a change in signal level is delayed by a predetermined time with respect to the detection signal based on the detection signal; and the detection signal and the delay signal are determined based on the detection signal and the delay signal. And a synchronizing signal generating means for generating a synchronizing signal having a signal level different between a period in which both are at the first signal level and a period other than the first signal level.

The detection signal generating means according to the first aspect of the present invention detects a light beam deflected by the deflecting means so as to scan the object to be scanned at a specific position within a scanning range of the light beam, and detects the light beam. Generates a detection signal having a first signal level during a period when the signal passes through a specific position, and a second signal level during other periods. Incidentally, this detection signal is a period other than a period during which the light beam passes through the specific position (a period during which the detection signal is at the second signal level).
In addition, a pulse-like signal level change corresponding to the external noise occurs due to the influence of the external noise, and the signal level may instantaneously become the first signal level.

On the other hand, the delay means according to the first aspect of the present invention generates a delay signal having a change in signal level delayed by a predetermined time with respect to the detection signal based on the detection signal. , Based on the detection signal and the delay signal, a synchronization signal having a signal level different between a period in which the detection signal and the delay signal are both at the first signal level and a period other than the first signal level.

In the present invention, the change period of the signal level when a pulse-like change corresponding to external noise occurs in the signal level of the detection signal is, in most cases, a very short period of about several nanoseconds. Has been confirmed by Therefore,
By appropriately setting the delay time (predetermined time) by the delay means (for example, making the signal level change period longer than the signal level change period when the change in the signal level corresponding to the external noise occurs in the detection signal), Even if the level instantaneously becomes the first signal level due to the influence of the external noise, it is possible to prevent both the detection signal and the delay signal from becoming the first signal level, and to be independent of the scanning speed of the light beam. In other words, it is possible to prevent the signal level of the synchronization signal from changing due to the influence of external noise during a period other than the period when the light beam passes through the specific position.

On the other hand, the period during which the detection signal is at the first signal level varies depending on the scanning speed of the light beam, but is at least several hundred nanoseconds, and the signal level of the detection signal is affected by external noise. Is obviously longer than the period during which it is changing. Therefore, by appropriately setting the delay time (predetermined time) by the delay means (for example, making it shorter than the period during which the detection signal is at the first signal level), the light beam can be output regardless of the scanning speed of the light beam. When the signal passes through the specific position, a period in which the detection signal and the delay signal are both at the first signal level can be generated.

Thus, during a period during which the light beam passes through the specific position (specifically, after the detection signal has reached the first signal level and a predetermined time has elapsed, the detection signal is changed from the first signal level to the second signal level). The signal level of the synchronizing signal during the period until the signal level changes to the other signal level differs from the signal level in other periods regardless of the scanning speed of the light beam. Therefore, according to the first aspect of the present invention, even if the scanning speed of the light beam is changed, it is possible to generate the synchronization signal without the influence of the external noise without changing the delay time by the delay unit.

The delay means according to the present invention can be realized by a circuit having a simple configuration such as a delay circuit (for example, a CR time constant circuit or a delay circuit using a logic gate) for delaying a detection signal for a predetermined time. Further, the synchronization signal generating means according to the present invention can also be realized by a circuit having a simple configuration such as a logic circuit. For example, assuming that the first signal level is at a high level and the second signal level is at a low level, the synchronizing signal generation means can be constituted by a logic circuit for calculating a logical product (AND).
Assuming that the signal level is low and the second signal level is high, the synchronizing signal generation means can be constituted by a logic circuit that performs a NAND operation (NAND).

Further, when the scanning speed of the light beam is changed, or when the scanning speed of the light beam is increased or decreased, the period of the detection signal is changed, Japanese Patent No. 288012 is also disclosed.
Processing such as changing the count value set in the counter as in No. 0 is not required. Therefore, the present invention also has an effect that the influence of external noise can be eliminated with a simple configuration.

In the present invention, the delay time by the delay means (the predetermined time according to the present invention) is, for example, the minimum of the period during which the detection signal is at the first signal level. The value of the signal level when the detection signal is shorter than a value (for example, a value corresponding to the fastest scanning speed in a mode in which a plurality of types of light beam scanning exist) and a change in the signal level corresponding to external noise occurs in the detection signal. Can be used for a time longer than the change period.

More specifically, in a general optical scanning device, when a photoelectric conversion element is arranged so that the light beam enters when passing through a specific position within the scanning range of the light beam, the light beam is The period during which the level of the detection signal output from the photoelectric conversion element changes as it passes through the specific position is at least about 300 nsec, and is a signal corresponding to external noise generated in the detection signal due to electromagnetic waves or the like. Considering that most of the level change has a pulse width of about several nanoseconds, the delay time (predetermined time according to the present invention) by the delay means is, as described in claim 3, from 50 nanoseconds to
The time can be in the range of 200 ns.

By setting the delay time of the delay means as described above, even when the scanning speed of the light beam is high, the detection signal is not changed before the delay signal changes from the second signal level to the first signal level. Changes from the first signal level to the second signal level, so that there is no period during which both the detection signal and the delay signal are at the first signal level, and the synchronization is performed while the light beam passes through the specific position. It is possible to avoid that the signal level of the signal does not occur, and it is possible to reliably eliminate the influence of external noise.

Incidentally, the detection signal generating means according to the present invention can be configured to include, for example, a single photoelectric conversion element arranged so that a light beam passing a specific position crosses a light receiving surface. The signal level of the signal output from the photoelectric conversion element becomes the second signal level when the light beam is not incident on the light receiving surface, and when the light beam crosses the light receiving surface of the photoelectric conversion element, The second signal level changes from the second signal level to the first signal level at a certain rate of change or vice versa according to the increase or decrease of the area of the area on the surface irradiated with the light beam.

However, in the above configuration, when the light amount of the light beam changes, the first signal level itself changes and the rate of change (gradient of change) of the signal level also changes. If the detection signal is generated by comparing the level of the signal output from the detector with the threshold value, the position of the light beam at the timing when the signal level of the detection signal is switched may vary depending on the light amount of the light beam. There is.

For this reason, the detection signal generating means according to the present invention comprises, as described in claim 4, a pair of photoelectric conversion elements arranged so that a light beam passing through a specific position sequentially crosses a light receiving surface. It is preferable that a detection signal is generated by comparing levels of signals output from the pair of photoelectric conversion elements. Since the signals output from the pair of photoelectric conversion elements show the same change with respect to the fluctuation of the light amount of the light beam, the detection signals are generated by comparing the levels of the signals output from the pair of photoelectric conversion elements. Thus, it is possible to obtain a detection signal whose signal level switches at an accurate timing with respect to the movement of the irradiation position of the light beam, irrespective of the fluctuation of the light amount of the light beam.

According to a fifth aspect of the present invention, there is provided an optical scanning device, comprising: a light source for emitting a light beam; and a deflecting means for deflecting the light beam so that the light beam emitted from the light source scans on the object to be scanned. And a signal level of a synchronization signal generated by the synchronization signal generation device according to any one of claims 1 to 4, wherein both the detection signal and the delay signal are the first signal. And a modulating means for modulating a light beam emitted from the light source with reference to a timing at which the signal level has changed from the signal level during the period of the signal level to the signal level during the other periods. I have.

An optical scanning device according to a fifth aspect of the present invention includes the synchronization signal generating device according to any one of the first to fourth aspects. As with the invention, regardless of the scanning speed of the light beam,
It is possible to obtain a synchronization signal from which the influence of external noise has been eliminated.

The signal level of the synchronizing signal generated by the synchronizing signal generation device is determined when the detection signal and the delay signal both reach the first signal level (ie, when the detection signal reaches the first signal level). After the predetermined time has elapsed from the first signal level, and the detection signal changes from the first signal level to the second signal level. At the timing when the signal level of the synchronizing signal changes as the detection signal changes from the first signal level to the second signal level, the light beam is always constant within the scanning range regardless of the scanning speed of the light beam. , But the detection signal is the first
The position of the light beam in the scanning range at the timing when the signal level of the synchronizing signal changes with the elapse of a predetermined time after the signal level reaches the signal level changes depending on the scanning speed of the light beam.

[0026] Based on the above, the modulating means according to the invention of claim 5 is characterized in that the signal level of the synchronizing signal generated by the synchronizing signal generating device is such that both the detection signal and the delay signal are the first signal.
Since the light beam is modulated based on the timing at which the signal level changes from the signal level during the period of the signal level to the signal level during the other periods, regardless of the scanning speed of the light beam, it is affected by external noise. It is possible to modulate the light beam at a fixed timing.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. In the following, description will be made using numerical values that do not hinder the present invention, but it goes without saying that the present invention is not limited to the numerical values described below.

FIG. 1 shows an optical scanning device 10 including a synchronization signal generating device according to the present invention.
The optical scanning device 10 includes a laser diode (LD) 12 as a light source according to claim 5. On the light beam emission side of the LD 12, a collimator lens 14, an aperture 16, a cylindrical lens 18 having power only in a certain direction (a direction corresponding to a sub-scanning direction described later),
The reflection mirrors 20 are arranged in order, and the reflection mirror 20
A rotary polygon mirror 22 as a deflecting means according to the fifth aspect is disposed on the light beam emission side of (5).

The light beam emitted from the LD 12 is converted into a parallel light beam by the collimator lens 14, shaped by the aperture 16, converged in the sub-scanning direction by the cylindrical lens 18, and then reflected by the reflection mirror 20 to be rotated by the polygon mirror. 22.

The rotary polygon mirror 22 is formed in a regular polygonal column shape, and has a plurality of reflection surfaces formed on its side surface, and each reflection surface is arranged so as to extend along a vertical direction. Rotating polygon mirror 22
Is rotated at a predetermined angular velocity by a driving means such as a motor (not shown) around the axis of the regular polygonal prism. With the rotation of the rotating polygon mirror 22, the light beam incident on the rotating polygon mirror 22 is reflected by the reflecting surface and is deflected and scanned. In addition,
Hereinafter, the direction of deflection of the light beam by the rotating polygon mirror 22 is referred to as a main scanning direction, and the direction orthogonal to the main scanning direction is referred to as a sub-scanning direction.

On the light beam emission side of the rotary polygon mirror 22, f
θ lens 24, cylindrical lens 26 having power only in the direction corresponding to the sub-scanning direction, photosensitive drum 28
Are arranged in order. The light beam deflected by the rotary polygon mirror 22 passes through the fθ lens 24 and has a beam width along a direction corresponding to the sub-scanning direction having a cylindrical lens 26.
After being converged, an image is formed as an optical spot on the peripheral surface (scanned surface) of the photosensitive drum 28.

The irradiation position of the light beam scans the peripheral surface of the photosensitive drum 28 at a constant speed (main scanning) along the direction parallel to the axis of the photosensitive drum 28 with the rotation of the rotary polygon mirror 22. ) Is done. The sub-scanning is performed by transmitting the driving force of a motor (not shown) and rotating the photosensitive drum 28.

The light beam emission side of the fθ lens 24 is located at the end (SO
Folding mirror 3 at a position corresponding to S: Start Of Scan)
The light beam reflected by the turning mirror 30 is incident on the beam position detection sensor 32.
The light beam emitted from the LD 12 is turned back when the one of the reflecting surfaces of the rotary polygon mirror 22 that reflects the light beam is oriented so as to reflect the incident beam in a direction corresponding to the SOS. The light is reflected at 30 and enters the beam position detection sensor 32.

The beam position detection sensor 32 constitutes a part of the synchronization signal generator 34 according to the present embodiment. The configuration of the synchronization signal generator 34 including the beam position detection sensor 32 will be described later.
From 4, a start position signal (SOS signal) which is normally at a low level and is at a high level for a fixed period (every time a light beam enters the beam position detection sensor 32) and for a fixed short period of time
Is output.

The synchronizing signal generator 34 is connected to the synchronizing pixel clock generator 36, and the SOS signal is input to the synchronizing pixel clock generator 36. The synchronous pixel clock generator 36 generates a pixel clock PX synchronized with the SOS signal (light beam scanning cycle) based on the input SOS signal.
Generate CK. The synchronous pixel clock generator 36 is connected to a modulation signal generator 38 and an image processing device (not shown), and outputs the generated pixel clock PXCK to the modulation signal generator 38 and the image processing device, respectively.

The modulation signal generator 38 is connected to the image processing device, from which an image signal representing an image to be formed on the peripheral surface of the photosensitive drum 28 is synchronized with the pixel clock PXCK. Are sequentially input at the specified timing. The modulation signal generator 38 performs modulation for scanning and exposing the image represented by the image signal onto the photosensitive drum 28 with a light beam at a timing synchronized with the pixel clock PXCK based on the input pixel clock PXCK and image signal. Generate a signal. The modulation signal generated by the modulation signal generator 38 is input to a laser driving device 40 connected to the modulation signal generator 38, and the laser driving device 40 drives the LD 12 based on the input modulation signal.

As a result, a light beam modulated according to an image to be formed on the peripheral surface of the photosensitive drum 28 is emitted from the LD 12, and the main scanning of the light beam by the rotating polygon mirror 22 and the photosensitive drum 28 With the sub-scan due to the rotation of
The image is formed on the peripheral surface of the photosensitive drum 28 by scanning exposure. Incidentally, the synchronous pixel clock generator 36, the modulation signal generator 38 and the laser driving device 40 correspond to the modulating means according to the fifth aspect.

Next, the synchronization signal generator 34 according to this embodiment will be described. As shown in FIG. 2B, the beam position detection sensor 32 of the synchronization signal generation device 34 includes a pair of photodiodes 44 whose cathodes are connected to each other.
A, a common cathode type two-division type photodiode 44 composed of A and 44B. As shown in FIG. 2A, the photodiodes 44A and 44B have light receiving surfaces such that the light beams incident on the beam position detection sensor 32 sequentially pass through the light receiving surfaces of the photodiodes 44A and 44B. They are arranged at predetermined intervals along the scanning direction of the beam.

The cathodes of the photodiodes 44A and 44B are connected to a DC power supply (not shown), and a constant voltage V _CC is applied by the DC power supply. Photodiode 4
The anode of 4A is grounded via a load resistor 46A, and the pulse signal generating circuit 5 is connected via a signal line 48A.
2 (see FIG. 1). The anode of the photodiode 44B is grounded via a load resistor 46B, and is connected to a pulse signal generation circuit 52 via a signal line 48B. A resistor 50 is connected to the signal line 48B.
And the other end of the resistor 50 is connected to the cathodes of the photodiodes 44A and 44B.

As a result, when the light beam sequentially passes through the light receiving surfaces of the photodiodes 44A and 44B, a signal having a waveform as shown by a solid line in FIG. Is the signal line 48A
5B, a signal having the same waveform as the sensor output A and slightly delayed in phase (hereinafter referred to as a sensor output B) is output from the photodiode 44B as a signal line 48B. Is output via. The amount of delay of the phase of the sensor output B with respect to the sensor output A depends on the photodiodes 44A and 44B along the scanning direction of the light beam.
This corresponds to the time required for the light beam to scan a distance corresponding to the positional shift amount of the light receiving surface, and when the scanning speed of the light beam is changed, the delay amount of the phase also changes.

The resistor 50 is connected to the beam position detecting sensor 3.
2 is provided to prevent the output of the comparator 54 (see FIG. 3A) of the pulse signal generation circuit 52 from oscillating during the period when the light beam is not incident on the sensor output A and the sensor output A. The signal level of the output B is slightly different due to the influence of the resistor 50 (see “offset potential” in FIG. 5C).

The offset potential is obtained by setting the electric resistance of the load resistor 46A to R1 and the electric resistance of the load resistor 46B to R1.
2. Assuming that the electric resistance value of the resistor 50 is R3, the offset potential is determined by: (R1 / (R2 + R2)) × VCC. As an example, R1 = R2 = 560 [Ω], R3 = 2
Assuming that 20 kΩ and VCC = 5 V, offset potential = (560 / (560 + 220 × 10 ³ )) × 5 = 12.7
[MV]. Since the offset potential in the present embodiment is a slight potential of the above value, it does not adversely affect the position detection accuracy of the light beam.

As shown in FIG. 3A, the pulse signal generation circuit 52 has a comparator 54, and the sensor output A is input to the non-inverting input terminal of the comparator 54 via the signal line 48A. The output B is input to the inverting input terminal of the comparator 54 after the level is once inverted via the signal line 48B (see FIG. 5C). The comparator 54 compares the signal level of the signal A input through the non-inverting input terminal with the signal level of the signal B obtained by inverting the level of the signal input through the inverting input terminal,
If the signal level of the signal A is higher than the signal level of the signal B, the output signal is set to the high level, and if the signal level of the signal A is equal to or lower than the signal level of the signal B, the output signal is set to the low level.

As a result, the detection signal (corresponding to the detection signal according to the present invention) output from the comparator 54 is such that a light beam is incident on the beam position detection sensor 32 as shown in FIG. During a period in which no signal is input, the signal is always at the low level (the second signal level according to the present invention). Also, during the period when the light beam is incident on the beam position detection sensor 32,
When the area of the light beam irradiation area on the light receiving surface of the photodiode 44A gradually increases with the movement of the light beam irradiation position, the signal level of the sensor output A also gradually increases, and the signal level of the sensor output A decreases. When the signal level becomes higher than the signal level of the output B, the detection signal switches from the low level to the high level (the first signal level according to the present invention).

When the area of the light beam irradiation area on the light receiving surface of the photodiode 44A gradually decreases with the movement of the light beam irradiation position, the signal level of the sensor output A also gradually decreases. At the same time, the signal level of the sensor output B gradually increases as the area of the light beam irradiation area on the light receiving surface of the photodiode 44B gradually increases. Then, at the timing when the center of the light beam irradiation area passes through a predetermined position in the gap between the light receiving surface of the photodiode 44A and the light receiving surface of the photodiode 44B, the signal level of the sensor output A becomes equal to or less than the signal level of the sensor output B, The detection signal returns from the high level to the low level.

As described above, the pair of photodiodes 44 disposed at positions shifted along the scanning direction of the light beam.
A, 44B (sensor outputs A, 44B)
By generating a detection signal by comparing the signal levels of B), even if the irradiation light amount of the light beam fluctuates, the signal levels of the sensor outputs A and B similarly change with a phase difference corresponding to the light beam scanning speed. Therefore, when the signal level of the sensor output A becomes equal to or lower than the signal level of the sensor output B, the light beam irradiation position at the timing when the detection signal switches from the high level to the low level depends on the fluctuation of the irradiation light amount of the light beam. Is always constant.

The pulse signal generation circuit 52 corresponds to the detection signal generation means of the present invention together with the beam position detection sensor 32. The photodiodes 44A and 44B correspond to a pair of photoelectric conversion elements described in claim 4,
The comparator 54 corresponds to the means for “comparing the levels of the signals output from the pair of photoelectric conversion elements”.

The pulse signal generation circuit 52 is connected to the SOS mask circuit 56, and the detection signal generated by the pulse signal generation circuit 52 is input to the SOS mask circuit 56. As shown in FIG. 3A, the SOS mask circuit 5
Reference numeral 6 denotes a delay signal obtained by delaying the detection signal input from the pulse signal generation circuit 52 by a predetermined time (an arbitrary value within a range of 50 to 200 nsec, for example, about 100 nsec) (see FIG. 5E). Is provided. The delay circuit 58 corresponds to the delay unit of the present invention.

FIG. 4A shows an example in which a CR time constant circuit is applied as the delay circuit 58. In this example, the signal input terminal of the delay circuit is connected to one end of the resistor 70,
Is connected to the other end of the capacitor 72, one end of which is grounded, and to the input terminal of an inverting gate circuit 74 with hysteresis input (for example, 74HC14). The output terminal of the inversion gate circuit 74 with hysteresis input is connected to the inversion gate circuit 7 with hysteresis input of the same configuration.
6 and the output terminal of the inverting gate circuit 76 with hysteresis input is connected to the output terminal of the delay circuit 58.

In the delay circuit shown in FIG. 4A, assuming that the electric resistance value R4 of the resistor 70 is 1.2 kΩ and the capacitance C1 of the capacitor 72 is 330 pF, the CR time constant is about Since this is 125 ns, the detection signal input to the delay circuit passes through the CR circuit and has a waveform shown as a signal D1 in FIG. 4B, and this signal is input to the inverting gate circuit 74 with a hysteresis input. The signal output from the inverting gate circuit 74 with the hysteresis input is shown in FIG.
FIG. 4B shows a waveform as a signal D2. Further, when this signal is input to the inverting gate circuit with hysteresis input 76, the signal output from the inverting gate circuit with hysteresis input 76 becomes the signal shown in FIG. As indicated by D3, the change in the signal level of the detection signal input to the delay circuit is delayed by 100 ns and becomes a waveform signal. Incidentally, instead of applying the CR time constant circuit as described above as the delay circuit 58, it is also possible to configure the logic circuit with a logic gate.

The delay signal output from the delay circuit 58 is
The detection signal input from the pulse signal generation circuit 52 is input to the AND circuit 60 together with the detection signal, and the AND circuit 60 outputs an SOS signal (see FIG. 5F). The SOS signal is a signal corresponding to the logical product of the detection signal and the delay signal. Therefore, the SOS signal is at a high level only when both the detection signal and the delay signal are at a high level, and when at least one of the detection signal and the delay signal is at a low level. Goes low. Note that AN
The D circuit 60 corresponds to the synchronizing signal generation means of the present invention, and the SOS signal corresponds to the synchronizing signal according to the present invention.

In this embodiment, the beam position detection sensor 32, the pulse signal generation circuit 52, and the SOS mask circuit 56 constituting the synchronization signal generation device 34 are integrally mounted on the same substrate. However, it is not an essential requirement to mount them on the same substrate. For example, the beam position detection sensor 32 and the pulse signal generation circuit 52 are arranged in the housing of the optical scanning device 10 and the SOS mask circuit 5
6 is disposed outside the housing, and the detection signal output from the pulse signal generation circuit 52 is
SO through the wire harness connecting the OS mask circuit 56
The signal may be input to the S mask circuit 56.

Next, the operation of the present embodiment will be described. When the LD 12 is driven by the laser driving device 40, the LD
When a light beam is emitted from the light source 12 and the rotary polygon mirror 22 is rotated by a motor (not shown), the light beam is incident on the beam position detection sensor 32 at the same cycle as the scanning cycle of the light beam. Thereby, as shown in FIG. 5 (F), the beam position detection sensor 3
Each time a light beam is incident on the S2, an SOS signal is generated in which a signal level change (detection pulse) that becomes high only during a period when both the detection signal and the delay signal are high.

The SOS signal is supplied to the synchronous pixel clock generator 36.
The synchronous pixel clock generator 36 generates the pixel clock PXCK based on the timing when the input SOS signal switches from the high level to the low level. A modulation signal is generated at a timing synchronized with the pixel clock PXCK, and the LD 12 is driven based on the generated modulation signal, whereby an image is formed on the peripheral surface of the photosensitive drum 28 by scanning exposure.

By the way, the photodiodes 44A, 44
The signal output from B (sensor outputs A and B) and the detection signal output from the comparator 54 are mixed with external noise due to electromagnetic waves or the like. As shown, a pulse-like signal level change may occur. This signal level change is S
If it is added to the OS signal, problems such as disturbance of the image formed on the peripheral surface of the photosensitive drum 28 occur.

However, the period during which the signal level is changed due to the mixing of external noise is a very short period of about several nanoseconds. In the present embodiment, however, the delay time of the delay circuit 58 is set to 50 nsec to 200 nsec. , Which is longer than the period during which the signal level is changed due to the incorporation of external noise, the delay signal output from the delay circuit 58 as shown in FIG. As in the case of the detection signal, a pulse-like signal level change appears, but the period in which the signal level of the detection signal changes in a pulse shape and the period in which the signal level of the delay signal changes in a pulse shape are temporal. (There is no period during which both the detection signal and the delay signal are at the high level.)

Since the SOS signal is a signal corresponding to the logical product of the detection signal and the delay signal, the period in which both the detection signal and the delay signal are at the high level does not occur, as shown in FIG. As shown in FIG. 2), the pulse-like signal level does not change in the SOS signal, and problems such as disturbance of the image formed on the peripheral surface of the photosensitive drum 28 are avoided. can do.

In this embodiment, the influence of external noise is eliminated by using a signal corresponding to the logical product of the detection signal and the delay signal as the SOS signal, so that the rotation speed of the rotary polygon mirror 22 is changed. As a result, even if the scanning speed (scanning cycle) of the light beam is changed and the cycle of the detection signal is changed in accordance with the change, for example, the processing by changing the delay time in the delay circuit 58 or the like is not performed. It is possible to prevent a pulse-like signal level change from occurring in the SOS signal.

On the other hand, the delay time in the delay circuit 58 is
If the detection signal is longer than the period when the detection signal is at the high level when the light beam is incident on the beam position detection sensor 32, the detection signal and the delay signal are also generated during the period when the light beam is incident on the beam position detection sensor 32. There is no longer a period in which both are at the high level, and even if a light beam is incident on the beam position detection sensor 32, there is an inconvenience that a level change (detection pulse) does not occur in the SOS signal.

On the other hand, during the period when the detection signal is at the high level when the light beam is incident on the beam position detection sensor 32, it varies according to the scanning speed of the light beam, but at least several hundred n This is on the order of seconds, and is clearly longer than the signal level change period when the signal level of the detection signal due to external noise changes in a pulse shape.

In the present embodiment, the delay time in the delay circuit 58 is set to an arbitrary value within the range of 50 ns to 200 ns. For example, by changing the scanning speed (scanning cycle) of the light beam, the beam position detecting sensor is changed. Even if the length of the period during which the detection signal is at the high level changes in accordance with the incidence of the light beam on 32, the delay time in the delay circuit 58 is smaller than the shortest value during the period during which the detection signal is at the high level. By setting so as to prevent a pulse-like signal level change due to extraneous noise from occurring in the SOS signal, and to ensure that the detection pulse is included in the SOS signal when the light beam enters the beam position detection sensor 32. Can be compatible. Therefore, even if the scanning speed of the light beam is changed, it is possible to generate the SOS signal in which the influence of the external noise is eliminated without performing the processing such as changing the delay time by the delay circuit 58.

The light beam irradiation position at the timing when the detection signal switches from the high level to the low level is always constant even if the scanning speed of the light beam changes, and the SOS signal also changes from the high level to the low level at the above timing. Switch to level. Since the synchronous pixel clock generator 36 generates the pixel clock PXCK based on the timing when the SOS signal switches from the high level to the low level,
Irrespective of the change in the scanning speed of the light beam, the photosensitive drum 2
An image can be formed at a fixed position on the peripheral surface of the image forming device 8.

Next, an appropriate delay time in the delay circuit 58 will be described with specific numerical values. As an image forming apparatus on which the optical scanning device 10 described in the embodiment of the present invention is mounted, a medium-sized image that sequentially forms images at a speed of 50 sheets per minute on A4 size paper conveyed in the longitudinal direction Assuming an image forming apparatus having a forming speed, the process speed (peripheral speed) of the photosensitive drum 28 is 220 mm /
Seconds. In addition, 600 dpi by a single light beam
The scanning cycle of the light beam is 192 μsec under the condition that the image is recorded at the recording density of, and the effective scanning rate for the photosensitive drum 28 (the image is actually recorded on the photosensitive body during one scanning time of the scanning optical system). Assuming that the time ratio is 90%, the distance (42.3 μ) corresponding to one pixel on the peripheral surface of the photosensitive drum 28 is obtained.
m), the time required for the light beam irradiation position to move by 25 nsec (the frequency of the pixel clock PXCK is 40 MHz)
_Z ), the scanning speed of the light beam is 1.7 μm / n second.

As an image forming apparatus having the same performance as the above conditions, for example, DocuColor 125 manufactured by Fuji Xerox
0 Although the like, because at the same time by scanning the two light beams in the apparatus is configured to perform the scanning exposure of the image, the frequency of the pixel clock of 1/2 of the above conditions 20MH _Z
It is about. Considering that most of the image forming apparatuses of this class on the market or higher-speed image forming apparatuses are configured to scan and expose an image by simultaneously scanning a plurality of light beams, it is mentioned above. The condition is that the light beam is scanned at a very high scanning speed which is about twice as high as that of the existing image forming apparatus.

On the other hand, as an example of a device that can be used as the photodiode 44 described in the embodiment of the present invention, light reception of a photodiode (S2545-02 manufactured by Hamamatsu Photonics) of a general two-division type in both shape and size is used. FIG. 6 is an enlarged view of the portion. The light receiving portion of this photodiode has a rectangular shape with a long side of 3 mm and a short side of 1.2 mm,
The light receiving unit is divided into two light receiving units corresponding to a pair of photodiodes by a slit having a width of 30 μm formed at the center of the light receiving unit in parallel with the long side, and the width of the light receiving unit corresponding to a single photodiode ( The dimension along the light beam scanning direction) is 585 μm.

The light receiving portion of the photodiode has a beam diameter of 60 μm in the scanning direction of the light beam and a beam diameter of 7 μm in the direction orthogonal to the scanning direction (sub-scanning direction).
If a 0 μm light beam (light spot) passes,
The time required for the light spot to pass through the light receiving unit corresponding to the single photodiode is 360 ns, and the sensor output A output from the photodiode A, which is located on the upstream side in the beam scanning direction, and the light receiving unit As shown in FIG. 7A, the sensor output B output from the photodiode B positioned downstream in the beam scanning direction rises within 34 nsec after the light spot hits the light receiving unit.
After maintaining the high level for 306 n seconds, the waveform falls over 34 n seconds. If the sensor outputs A and B of this waveform are input to the comparator 54, respectively,
4 is at a high level for 360 nsec.

As is apparent from the above, even when the light beam is scanned at a very high scanning speed which is about twice as high as that of the existing image forming apparatus, the period during which the detection signal is at the high level is 300 ns. The delay time in the delay circuit 58 is set to 50 nsec to 200 nsec in consideration of a period in which a pulse-like change occurs in the signal level of the detection signal when external noise is mixed.
With a value of n seconds, it is possible to generate an SOS signal excluding the influence of external noise, regardless of the scanning speed of the light beam.

In the above description, the detection signal is delayed based on a detection signal which is normally at a low level and temporarily becomes a high level when the light beam enters the beam position detection sensor 32, and a delay signal is generated. , The case where the SOS signal corresponding to the logical product of the detection signal and the delay signal is generated,
The detection signal is a signal of negative logic with respect to the above detection signal (usually a high level signal which temporarily goes to a low level when a light beam enters the beam position detection sensor 32).
In this case, a signal corresponding to the NAND of the detection signal and the delay signal may be generated as the SOS signal.

In the above description, the case where the timing at which the light beam is deflected in the direction corresponding to the SOS has been described as an example. However, the present invention is not limited to this. Of which, the end on the scan end side (EO
It can also be applied to the case where the timing at which the light beam is deflected in a direction corresponding to S: End Of Scan) is detected.

In the above description, a configuration has been described in which a light beam is detected by a pair of photoelectric conversion elements (photodiodes 44A and 44B) arranged so that the light beam sequentially crosses the light receiving surface. However, the present invention is not limited to this, and a configuration in which a light beam is detected by a single photoelectric conversion element may be used.

Further, the synchronizing signal generated by the synchronizing signal generating device according to the present invention is not limited to use for controlling the modulation start timing as described above.
For example, the present invention is applied to an optical scanning device configured to deflect and scan a plurality of light beams, and the timing at which each light beam passes a specific position (for example, a position corresponding to SOS or EOS) within a scanning range is determined. Generate a synchronization signal that represents
By comparing the generated synchronization signals, it is possible to detect the relative displacement of a plurality of images formed by the individual light beams.

[0072]

As described above, according to the first aspect of the present invention, the signal level becomes the first signal level while the light beam passes through the specific position within the scanning range, and the signal level becomes the first signal level during the other periods. A delay signal in which the change in the signal level is delayed by a predetermined time with respect to the detection signal, and a period in which both the detection signal and the delay signal are at the first signal level. Since a synchronizing signal having a signal level different from that of other periods is generated, there is an excellent effect that a synchronizing signal free of the influence of external noise can be generated regardless of the scanning speed of the light beam.

According to a second aspect of the present invention, in the first aspect of the invention, the change in the signal level corresponding to the external noise is shorter than the minimum value during the period when the detection signal is at the first signal level. Since the delay signal is generated by delaying the detection signal by a time longer than the normal change period of the signal level when the detection signal occurs, in addition to the above effects, even when the scanning speed of the light beam is high, the light beam Has the effect that the signal level of the synchronization signal does not occur while passing through the specific position, and the effect of external noise can be reliably eliminated.

According to a third aspect of the present invention, in the first aspect of the present invention, the detection signal is delayed by a time within a range of 50 ns to 200 ns to generate a delayed signal. Even when the scanning speed is high, it is possible to avoid that the signal level of the synchronization signal does not occur while the light beam passes through the specific position, and it is possible to surely eliminate the influence of external noise. Having.

According to a fourth aspect of the present invention, in the first aspect of the present invention, a signal output from a pair of photoelectric conversion elements arranged so that a light beam passing a specific position sequentially crosses a light receiving surface is provided. Since the detection signal is generated by comparing the levels, in addition to the above-described effects, a detection signal whose signal level switches at an accurate timing with respect to the movement of the irradiation position of the light beam is obtained irrespective of the fluctuation of the light amount of the light beam. Has the effect of being able to

According to a fifth aspect of the present invention, the signal level of the synchronization signal generated by the synchronization signal generation device according to any one of the first to fourth aspects is such that both the detection signal and the delay signal are the first signal. Since the light beam is modulated based on the timing at which the signal level changes from the signal level in the period during which the signal level is changed to the signal level in other periods, the light beam is fixed without being affected by external noise regardless of the scanning speed of the light beam. The light beam can be modulated at the timing described above.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical scanning device according to an embodiment.

FIG. 2A is a plan view showing an arrangement of light receiving surfaces of a pair of photodiodes of a beam position detection sensor, and FIG. 2B is a circuit diagram of the beam position detection sensor.

FIG. 3 is a block diagram illustrating a schematic configuration of a pulse signal generation circuit and an SOS mask circuit.

FIG. 4A is a circuit diagram illustrating an example of a delay circuit;
(B) is a timing chart for explaining the operation of the delay circuit shown in (A).

FIG. 5A is an image diagram for explaining a state in which a light beam irradiation area passes through a beam position detection sensor,
(B) is a sensor output A, B, (C) is a signal compared by a comparator, (D) is a detection signal, (E) is a delay signal,
(F) is a timing chart showing each example of the SOS signal.

FIG. 6 is a diagram illustrating an example of a shape of a light receiving unit of a photodiode and a beam diameter of a light beam for explaining an appropriate delay time in a delay circuit.

FIG. 7 (A) in the example of FIG.
7B is a diagram illustrating a waveform of a signal B, and FIG. 7B is a diagram illustrating a waveform of a detection signal output from the comparator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical scanning device 12 LD 22 Rotating polygon mirror 32 Beam position detection sensor 34 Synchronous signal generator 36 Synchronous pixel clock generator 38 Modulation signal generator 40 Laser drive 44 Photodiode 54 Comparator 58 Delay circuit 60 AND circuit

Claims (5)

[Claims] 1. A light beam deflected by a deflecting means so as to scan an object to be scanned at a specific position within a scanning range of the light beam, and a period during which the light beam passes through the specific position. A detection signal generating means for generating a detection signal having a first signal level and a second signal level in other periods; and a change in signal level based on the detection signal. A delay unit that generates a delay signal delayed by a predetermined time with respect to a period in which both the detection signal and the delay signal are at the first signal level and other periods based on the detection signal and the delay signal And a synchronizing signal generating means for generating a synchronizing signal having different signal levels. 2. The method according to claim 1, wherein the delay unit sets the predetermined time as:
The detection signal is shorter than the minimum value of the period during which the detection signal is at the first signal level, and is longer than the normal change period of the signal level when a change in the signal level corresponding to the external noise occurs in the detection signal. 2. The synchronization signal generation device according to claim 1, wherein the delay signal is generated by delaying the detection signal by a time. 3. The method according to claim 2, wherein the delay unit sets the predetermined time as:
2. The synchronization signal generation device according to claim 1, wherein the delay signal is generated by delaying the detection signal by a time within a range of 50 ns to 200 ns. 4. The detection signal generation means includes a pair of photoelectric conversion elements arranged so that a light beam passing through the specific position sequentially crosses a light receiving surface, and each of the detection signals is output from the pair of photoelectric conversion elements. 2. The synchronization signal generating apparatus according to claim 1, wherein the detection signal is generated by comparing the levels of the signals. 5. A light source for emitting a light beam, and a deflecting unit for deflecting the light beam so that the light beam emitted from the light source scans a scanning target. 2. The synchronization signal generation device according to claim 1, wherein the signal level of the synchronization signal generated by the synchronization signal generation device is a signal level during a period in which both the detection signal and the delay signal are at the first signal level. And a modulating means for modulating a light beam emitted from the light source with reference to a timing at which the signal level changes to a signal level in other periods.