JPH0376063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a beam position detection device for a laser beam scanning system.

[Prior art]

In laser beams, printers, reading devices, etc., a laser beam that forms a beam spot on a surface to be scanned, such as a recording surface or a reading surface, is deflected and controlled, and the surface to be scanned is scanned with the beam spot. In printers, scanning of the beam spot is performed in order to match the timing of modulating the laser beam with recorded information and the beam spot position, and in reading devices to match the beam spot position and the operation timing of the photoelectric conversion means. Start detection is performed. This scan start detection is performed by placing a photoelectric conversion type light receiving element in the laser beam deflection scanning optical path outside the effective area of the scanned surface, and detecting the output signal obtained when the laser beam spot scans this light receiving element. This is used as the scanning start detection reference signal.

However, if a deviation occurs in the mechanical dimensions of the laser beam scanning unit and the laser beam is no longer correctly irradiated onto the light receiving element, a detection error will occur, eventually making it impossible to detect the start of scanning. This problem appears particularly when the amount of positional deviation in the direction perpendicular to the scanning direction of the laser beam becomes large. This phenomenon will be explained with reference to FIG. A beam spot 2a is applied to a photoelectric conversion element such as a photodiode having a rectangular light-receiving surface 1a as shown in Fig. 1a.
When the photoelectric conversion element 1 is scanned, the detection output signal of the photoelectric conversion element 1 has the characteristic A shown in FIG. 1b. On the other hand, when the beam spot 2b is scanned, the photoelectric conversion element 1
The detection output signal has characteristic B. If the presence or absence of these output signals A and B is determined using a threshold value V _th , the start of scanning of the beam spot 2b (characteristic B) cannot be detected. If the presence/absence is determined using a threshold value V _th ' smaller than this, it is possible to detect the start of scanning of the beam spot 2b, but a detection error of Δt occurs with respect to the detection of the start of scanning of the beam spot 2a.
Moreover, by making the threshold value small, it becomes more susceptible to the influence of noise.

Therefore, in order to eliminate problems caused by misalignment between the light-receiving surface of the photoelectric conversion element and the beam spot in the perpendicular direction, the output signal of the photoelectric conversion element is observed using a synchroscope during assembly and maintenance, and the relative position can be determined. Adjustment work was being carried out. However, it is troublesome because it requires measuring equipment, and it also has the drawback that it is impossible to detect positional deviation when the device is in operation.

In order to detect the positional deviation state without using a measuring device and even when the device is in operation, a photoelectric conversion element for scanning positional deviation detection having light-receiving surfaces 3a and 3b is provided as shown in Fig. 2, and from this photoelectric conversion element It is conceivable to compare the magnitudes of the obtained output signals and detect the amount of deviation from the magnitude of the difference.
In this case, if the center of the beam spot 4 scans the intermediate position between the light receiving surfaces 3a and 3b of the two photoelectric conversion elements, the magnitudes of the detection signals of both photoelectric conversion elements are equal. If the beam spot scanning position deviates in either of the perpendicular directions, there will be a difference in the magnitude of the detection signal.
By arranging the two photoelectric conversion elements so that the magnitude of the detection signal is equal while scanning the center position of the beam spot, and observing the magnitude and its limit during operation, the amount of scanning position deviation of the beam spot can be determined. and the direction of deviation can be detected. However, even in this case, if the laser beam light intensity is uneven or there is a difference in photoelectric conversion characteristics between the two photoelectric conversion elements, a positional deviation detection error will occur, making it difficult to prevent the above-mentioned problems from occurring. Become.

[Purpose of the invention]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a beam position detection device that can reliably detect a scanning position shift in a direction perpendicular to the laser beam scanning direction in a laser beam scanning system while the scanning system is in operation.

[Summary of the invention]

In order to achieve this object, the present invention has a light-receiving surface whose width in the laser beam scanning direction sequentially changes according to the scanning position in a direction perpendicular to the scanning direction, and this light-receiving surface serves as a deflection scanning optical path of the laser beam. a photoelectric conversion means for outputting a photoelectric conversion output signal according to a scanning position in a direction perpendicular to the scanning direction of the beam spot disposed inside the beam spot and scanning the light-receiving surface; and the photoelectric conversion output signal obtained from the photoelectric conversion means. and comparison circuit means for comparing a reference signal corresponding to a photoelectric conversion output signal output when the beam spot scans a reference scanning position in a direction perpendicular to the scanning direction of the light receiving surface, and the comparison circuit means A scanning position shift in a direction perpendicular to the reference scanning position of the beam spot scanning the light receiving surface is detected using an output signal, and the time width of the detection output signal is used as a position detection element. This reduces detection errors due to variations in the photoelectric conversion characteristics of the photoelectric conversion means and the amount of beam spot light.

[Embodiments of the invention]

Figures 3 to 5 show an embodiment of the present invention. Figure 3 is an electric circuit diagram, Figure 4 is a diagram of the light receiving surface of the photoelectric conversion element and the detection signal waveform, and Figure 5 is a diagram of the scanning position shift. It is a detection characteristic diagram.

In FIG. 3, the photoelectric conversion element 5 is the operational amplifier 6.
The (-) input terminal of the operational amplifier 6 is connected between the (-) input terminal of the operational amplifier 6 and the negative power supply (-V), and the (+) input terminal of the operational amplifier 6 is grounded. The (+) input terminal of the comparator 7 is connected to the output terminal of the operational amplifier 6, and the (-) input terminal is connected to the threshold power supply (+V _th ). The integrating circuit 8 is composed of an operational amplifier 8a, a resistor 8b, and a capacitor 8c. The (-) input terminal of the operational amplifier 8a is connected to the output terminal of the comparator 7, and the (+) input terminal is grounded. The comparators 9 and 10 are for determining whether the scanning position of the beam spot scanning the light receiving surface of the photoelectric conversion element 5 is within a predetermined range of the light receiving surface. The (+) input terminal of the comparator 9 is connected to the output terminal of the integrating circuit 8, and the (+) input terminal of the comparator 9 is connected to the range setting power supply (-
V _e1 ) and the (-) input terminal of the comparator 10 are connected to a range setting power source (-V _e2 ), respectively.
Reference numerals 11 and 12 indicate light emitting diodes, which are respectively connected between the output terminals of the comparators 9 and 10 and the positive power supply (+V). Window type comparator 13
is for determining the limit of positional deviation of the beam spot scanning the light receiving surface of the photoelectric conversion element 5, and is composed of comparators 13a, 13b, resistors 13c, 13d, and diode 13e.
Each (-) input terminal of a, 13b is connected to the integrating circuit 8.
The (+) input terminal of the comparator 13a is connected to the limit setting power source (-V _ref1 ), and the (+) input terminal of the comparator 13b is connected to the limit setting power source (-V _ref2 ). A light emitting diode 14 is connected between the output terminal of the comparator 13b and the positive power supply (+V). A scanning start detection reference signal _Vs indicating that the beam spot has scanned the light receiving surface of the photoelectric conversion element 5 is obtained from the output terminal of the comparator 7.

In such an electric circuit, the photoelectric conversion element 5 has a starting edge that extends perpendicularly to the scanning direction of the beam spot 15 and a terminal edge that is inclined with respect to this starting edge, as shown in FIG. 4a, and has a width in the scanning direction. has a light-receiving surface 5a that varies sequentially depending on the scanning position, the output signal _Vs of the comparator 7 changes from _Vsa to the beam spot by repeatedly changing the scanning position of the beam spot 15a, as shown in FIG. 4b. 15b
By repeatedly scanning the scanning position, V _{sb .} . . is obtained. When this output signal V _s is integrated by the integrating circuit 8, the integrated output signal V ₀ changes depending on the scanning position as shown in FIG. 5a. When the scanning position of the beam spot 15c is the center and the adjustment is to be made between the scanning positions of the beam spots 15b and 15d, a voltage equal to the integral output signal -V _0b obtained by repeated scanning of the beam spot 15b is set. The integral output signal -V _0d obtained by setting the range setting power supply (-V _e1 ) and repeatedly scanning the beam spot 15d.
Set the range setting supply (−V _e2 ) to a voltage equal to . As a result, as shown in FIG. 5b, if the beam spot 15 repeatedly scans between the beam spots 15b and 15e, the two comparators 9 and 1
The output of 0 is high level and the light emitting diode 11,1
Both lights are off. and beam spot 1
The scanning position of 5 is from this range to the beam spot 15.
If it shifts to the side a, the output of the comparator 9 becomes low level and the light emitting diode 11 lights up, and conversely, if it shifts to the side of the beam spot 15e, the output of the comparator 9 goes low and the light emitting diode 11 lights up.
When the output of 0 becomes low level, light emitting diode 1
2 lights up. Therefore, when adjusting the scanning position of the beam spot 15, both light emitting diodes 11 and 12 may be turned off.

Further, assuming that the limit of the scanning position at which the photoelectric conversion element 5 can detect the scanning of the beam spot 15 is the scanning position of the beam spots 15a and 15e, the integral output signal -V obtained by repeated scanning of the beam spot 15a Set the limit setting power supply (-V _ref1 ) to a voltage far from _0a , and set the beam spot 15.
If the limit setting power source (-V _ref2 ) is set to a voltage equal to the integral output signal -V _0e obtained by repeated scanning of beam spot 15, the scanning position of beam spot 15 is within the range of beam spots 15a and 15e. In a state where the photoelectric conversion element 5 is detecting the scanning, the output of the comparator 13 becomes low level and the light emitting diode 14 lights up to notify this state.

Note that detection of the start of scanning of the beam spot 15 is performed based on the rise of the output signal V _sa of the comparator 7 .

According to the above configuration, the following effects can be obtained.

(a) Observing the scanning position deviation between the light-receiving surface of the photoelectric conversion element and the beam spot without using a measuring device,
Able to carry out adjustment work.

(b) Since the amount of scanning position deviation is detected according to the time width of the detection output of the photoelectric conversion element, it is less susceptible to changes in the light intensity of the laser beam spot or the sensitivity of the light intensity conversion element.

(c) Since the detection output of one photoelectric conversion element is processed by an electric circuit and used for scanning position detection and scanning start detection, the configuration of the photoelectric conversion means is simple.

In this embodiment, the scanning direction of the beam spot 15 with respect to the light receiving surface 5a of the photoelectric conversion element 5 may be reversed. However, in that case, it is necessary to detect the start of scanning based on the falling edge of the output signal V _sa of the comparator 7.

In the second embodiment shown in FIG. 6, a second photoelectric conversion element 16 is added to the first embodiment described in FIG. and further amplify it with comparator 1.
8 performs waveform shaping to obtain an output signal having a polarity opposite to that of the output signal of comparator 7, and the output signals of both comparators 7 and 18 are integrated by an integrating circuit 8.

In this second embodiment, as shown in FIG. If the beam spot 15 has a starting edge that is perpendicular to the scanning direction, and a terminal edge that is perpendicular to the scanning direction, and the widths of the light receiving surfaces 5a and 16a are equal at the central scanning position, the comparator 7, 18 output signals +V _s , -
V _s becomes +V _sa to -V _se in FIG. 7b. When both output signals +V _s and -V _s are integrated by an integrating circuit 8, an integrated output signal V ₀ changes depending on the scanning position as shown in FIG. 8a. At the repeated scanning position by the beam spot 15c, the output signal of the comparator 7 +V _sc and the output signal of the comparator 18 -
Since the time widths of V _sc are equal, the integral output signal V ₀ is zero, and when the beam spots 15a and 15b are repeatedly scanned, the integral output signal V ₀ is positive, and when the beam spots 15d and 15e are repeatedly scanned, the integral output signal V ₀ is negative. becomes. Therefore, the range setting power supply (+V _e1 ),
(-V _e2 ) are set to voltages equal to the integral output signals +V _0b and -V _0d , respectively, and the limit setting power supply (+V _ref1 ),
(−V _ref2 ) as integral output signals +V _0a and −V _0e , respectively.
If the voltage is set equal to , the same result as above can be obtained. Moreover, in this second embodiment, since the beam spot 15 detects the scanning position based on the difference in scanning time width between the light receiving surfaces 5a and 16a, the relative relationship between the widths of both the light receiving surfaces 5a and 16a can be accurately determined. Once set, changes in the absolute value and scanning speed will have little effect. Furthermore, as the scanning position of the beam spot 15 changes, the output time widths of the comparators 7 and 18 change in opposite characteristics, so that the integral output signal V ₀
The change in the value becomes larger, and the detection accuracy becomes higher.

Further, in this second embodiment, the falling edge of the output signal _-V0 of the comparator 18 can be used as a reference signal for detecting the start of scanning.

Further, the light receiving surfaces 5a, 16 of the photoelectric conversion elements 5, 16
The same effect can be obtained even if the starting edge and the ending edge of a are reversed. In these cases, scan start detection is chosen to be based on a change in the output signal at an edge perpendicular to the scan direction.

The third embodiment shown in FIGS. 9 and 10 is an example in which one photoelectric conversion element 5 is used as shown in FIGS. 3 to 5, and the signal processing thereof is digitized. The photoelectric conversion element 5 is connected between the (+) input terminal of the operational amplifier 6 and the positive power supply (+V), and the (-) input terminal of the operational amplifier 6 is grounded. The (+) input terminal of the comparator 7 is connected to the output terminal of the operational amplifier 6, and the (-) input terminal is connected to the threshold power supply (+
V _th ). The enable input terminal Enable of the digital counter 19 is connected to the output terminal of the comparator 7, the clock signal CLOCK is applied to the clock input terminal ck, and the clear signal CLEAR output from the delay circuit 20 is applied to the clear input terminal Clear. . The count output signal output from the counter 19 is latched by a latch circuit 21 triggered by a trigger signal TRIGER from a delay circuit 20, and the latched value is applied to a digital comparator 22 as a comparison value _Dio .
The output signal V _s of the comparator 7 is
9 and is used as a scan start detection reference signal, and is further input to the delay circuit 20 to generate the trigger signal TRIGER which latches the output of the counter 19 every scan, and then clears the counter 19. Clear signal CLEAR
It becomes the standard for generating. Comparator 22
compares the output signal Dio of the latch circuit 21 _with the reference value _Dref , and the comparison output signal is sent to the inverters 23 and 2.
4, 25 through light emitting diodes 26, 27, 2
given to 8.

In the above circuit configuration, the photoelectric conversion element 5
is the light-receiving surface 5a shown in FIG.
When c scans, an output signal _Vs is generated from the comparator 7 and the counter 19 is enabled, as shown in b in the same figure, and the clock signal during that period is
The number of CLOCKs N _c is counted. When the output signal V _s disappears, the delay circuit 20 generates the trigger signal TRIGER with a time delay of td ₁ and latches the count output signal of count 19 in the latch circuit 21 at the rising edge of the trigger signal TRIGER. Thereafter, a clear signal CLEAR is generated with a further delay of td ₂ hours, and the counter 19 is cleared. If the count output signal at this time, that is, the comparison value D _io given to the comparator 22 is _Dioc , then the light emitting diode 27 can be turned on by setting the reference value D _ref as D _ref =D _ioc . When the beam spot 15b scans the light receiving surface 5a, the comparison value D _io becomes D _iob and D _iob <D _ref , so the light emitting diode 26 lights up and the beam spot 15d
When scanning the light receiving surface 5a, the comparison value D _io is D _iod
Since D _iod > D _ref , the light emitting diode 28
lights up.

The fourth embodiment shown in FIGS. 11 and 12 is the sixth embodiment.
This is an example in which the signal processing is digitized using two photoelectric conversion elements 5 and 16 as in the second embodiment shown in FIGS. The photoelectric conversion elements 5 and 16 are the (+) of the operational amplifiers 6 and 17, respectively.
It is connected between the input terminal and the positive power supply (+V), and the (-) input terminal of each operational amplifier 6, 17 is grounded. Each (+) input terminal of the comparators 7, 18 is connected to the output terminal of the operational amplifier 6, 17, respectively, and each (-) input terminal is connected to the threshold power supply (+V _th ), respectively. The output signal V _s1 of the comparator 7 is used as a scanning start detection reference signal and is input to one input terminal of the NAND gate 29 . The output signal V _s2 of the comparator 18 is input to the delay circuit 20 and also to the NAND gate 3.
It is input to the 0 input terminal. Each NAND gate 2
The other input terminal of 9 and 30 has a clock signal.
CLOCK is input. The digital up/down counter 31 has an up count input terminal U _p .
The down-count input terminal Dowt is connected to the output terminal of the NAND gate 30, the initial value DATA is applied to the data input terminal Data, and this initial value DATA is input as a load input from the delay circuit 20. It is taken into the counter 31 by the load signal LOAD applied to the terminal Load. The count output signal output from the output terminal Q of the counter 31 is latched by a latch circuit 21 triggered by a trigger signal TRIGER from the delay circuit 20, and the latched value is applied to a digital comparator 22 as a comparison value _Dio .
The comparator 22 is the output signal of the latch circuit 21.
D _io is compared with a reference value D _ref , and the comparison output signal is applied to light emitting diodes 26 , 27 , 28 via inverters 23 , 24 , 25 .

In the above circuit configuration, the photoelectric conversion elements 5 and 16 have light receiving surfaces 5a and 16a shown in FIG. 12a.
When the beam spot 15c scans the central scanning position of the light receiving surfaces 5a and 16a, the light receiving surface 5a is first scanned and the output signal _Vs1 of the comparator 7 is generated, so that the clock signal CLOCK is
It is applied to the up count input terminal _Up of the up down counter 31 via the NAND gate 29,
Clock signal while output signal V _s1 is generated
Count up by the number of CLOCKs N _e1 . Next, the light receiving surface 16a is scanned and the output signal V _s2 of the comparator 18 is generated, so the clock signal CLOCK is generated.
is applied to the down-count input terminal Down of the up-down counter 31 via the NAND gate 30, and counts down by the number N _c2 of the clock signal CLOCK while the output signal V _s2 is being generated.
When the output signal V _s2 of the comparator 18 disappears,
The delay circuit 20 generates a trigger signal with a time delay of td ₁ .
TRIGER is generated and counter 3 occurs at the rising edge.
A count output signal of 1 is latched in the latch circuit 21. After that, the load signal is further delayed by TD ₂ hours.
When LOAD occurs, counter 31 contains the initial value.
DATA is imported. As a result, the output signal of the latch circuit 21, that is, the comparison value _Dio input to the comparator 22, is N _c1 in scanning at the center scanning position.
= N _c2 , so D _io = DATA.
Therefore, the reference value D _ref of the comparator 22 is set as D _ref =
If it is set as DATA, the light emitting diode 27 can be turned on. And beam spot 15
When b scans the light receiving surfaces 5a and 16a, the comparison value is
Since D _io becomes D _iob and D _iob <D _ref , the light emitting diode 26 lights up and when the beam spot 15d scans the light receiving surfaces 5a and 16a, the comparison value D _io becomes
Since D _iod becomes D _iod > D _ref , the light emitting diode 28 lights up.

The third and fourth embodiments described above are also similar to the first and second embodiments.
This embodiment can be modified and implemented in the same manner as the embodiment described above, and the same effects can be obtained.

In each of the above four embodiments, the photoelectric conversion elements 5 and 16 are used to detect the start of scanning, but a photoelectric conversion element dedicated to detecting the start of scanning may be provided at the same scanning position as these photoelectric conversion elements.

Further, the width of the light-receiving surface of the photoelectric conversion element in the scanning direction does not need to change continuously, but may be stepwise.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a light-receiving surface whose width in the laser beam scanning direction sequentially changes according to the scanning position in the direction perpendicular to the scanning direction, and the light-receiving surface is located in the deflection scanning optical path of the laser beam. a photoelectric conversion means for outputting a photoelectric conversion output signal in accordance with a scanning position in a direction perpendicular to the scanning direction of the beam spot disposed on the light receiving surface; and a photoelectric conversion output signal obtained from the photoelectric conversion means. comparison circuit means for comparing a reference signal corresponding to a photoelectric conversion output signal output when the beam spot scans a reference scanning position in a direction perpendicular to the scanning direction of the light receiving surface; Since the scanning position shift in the perpendicular direction with respect to the reference scanning position of the beam spot scanning the light receiving surface is detected by the signal, detection errors due to variations in the photoelectric conversion characteristics of the photoelectric conversion means and the light amount of the beam spot can be avoided. It has the effect of reducing

[Brief explanation of drawings]

Figures 1a and b are beam spot scanning and output characteristic diagrams for the light receiving surface of the photoelectric conversion means, Figure 2 is a diagram of the light receiving surface and beam spot scanning of the improved photoelectric conversion means, and Figures 3 to 12 are diagrams of the present invention. Embodiments of the invention are shown; FIG. 3 is an electric circuit diagram of the first embodiment, FIGS. 4a and 4b are beam spot scanning and output characteristic diagrams for the light receiving surface of the photoelectric conversion means, and FIGS. 5a to c 6 is an electric circuit diagram of the second embodiment, FIGS. 7 a and b are beam spot scanning and output characteristics diagrams for the light receiving surface of the photoelectric conversion means, and FIGS. 8 a to c is its position detection characteristic diagram, and Fig. 9 is the third
10a and 10b are the position detection signal waveform diagrams, FIG. 11 is the electrical circuit diagram of the fourth embodiment, and Figures 12a and 12b are the position detection signal waveform diagrams. be. 5...Photoelectric conversion element, 5a... Light receiving surface, 8...
Integrating circuit, 9, 10, 13... comparator.

Claims (1)

[Scope of Claims] 1. In a laser beam scanning system that scans a beam spot by controlling the deflection of a laser beam that forms a beam spot on a surface to be scanned, a scanning position whose width in the laser beam scanning direction is perpendicular to the scanning direction. The light receiving surface is arranged in the deflection scanning optical path of the laser beam and scans the light receiving surface. A photoelectric conversion means for outputting a conversion output signal, and a photoelectric conversion output signal obtained from the photoelectric conversion means and a photoelectric conversion output when the beam spot scans a reference scanning position in a direction perpendicular to the scanning direction of the light receiving surface. A comparison circuit means for comparing a reference signal corresponding to the converted output signal is provided, and a scanning position shift in a direction perpendicular to the reference scanning position of the beam spot scanning the light receiving surface is determined by the output signal of the comparison circuit means. 1. A beam position detection device for a laser beam scanning system, which detects the position of a laser beam. 2. In claim 1, the comparison circuit means includes an integration circuit that integrates the output signal of the photoelectric conversion means, and a discrimination circuit that determines the relationship between the output signal of the integration circuit and the reference signal. A beam position detection device of a laser beam scanning system, characterized in that: 3. In claim 1, the photoelectric conversion means is arranged side by side in the scanning direction, has the same width in the scanning direction at the reference scanning position in the orthogonal direction, and has opposite width change characteristics depending on the position in the orthogonal direction. a waveform shaping circuit comprising two photoelectric conversion elements having surfaces, the comparison circuit means waveform shaping the output signals obtained from the two photoelectric conversion elements so that the two output signals have opposite polarities; The present invention is characterized by comprising an integrating circuit that integrates these two output signals of opposite polarity and outputs the difference, and a discrimination circuit that determines the relationship between the magnitude of the output signal of the integrating circuit and the magnitude of the reference signal. Beam position detection device for laser beam scanning system. 4. In claim 1, the comparison circuit means includes a counter that counts clock pulses while the photoelectric conversion output signal is present, and a discrimination circuit that discriminates the relationship between the counted value of this counter and a reference value. A beam position detection device of a laser beam scanning system, characterized in that: 5. In claim 1, the photoelectric conversion means is arranged side by side in the scanning direction, has the same width in the scanning direction at the reference scanning position in the orthogonal direction, and has opposite width change characteristics depending on the position in the orthogonal direction. The comparison circuit means includes two photoelectric conversion elements having a surface, and the comparison circuit means counts up the clock pulse while the output signal of one photoelectric conversion element is present, and counts up the clock pulse while the output signal of the other photoelectric conversion element exists. 1. A beam position detection device for a laser beam scanning system, comprising: an up-down counter that counts down the up-down counter; and a determination circuit that determines the relationship between the counted value of the up-down counter and a reference value.