JPS5970359A - Beam position detector of laser beam scanning system - Google Patents

Abstract

PURPOSE:To detect surely the position shift in orthogonal direction to the scanning direction, by providing a photoelectric converting means having a photo detecting means where the width in the laser beam scanning direction is changed sequentially in response to the position orthogonal to the scanning direction, in a deflecting scanning optical path of a laser beam. CONSTITUTION:The photoelectric converting element 5 has photo detecting plane (Fig. a) having a start end prolonged in a direction orthogonal to the scanning direction of a beam spot and an end tilted to this start end, and the output signals Vsa-Vse are applied to an operational amplifier 6. Taking the center of the beam spot as a center 15c, and when adjusting the range between 15b and 15d, a range set power supply (-Ve1) of the operational amplifier 9 is made equal to an integration output signal obtained at the repetition of the spot 15b so as to set a range set power supply (-Ve2) of an operational amplifier 10 to the integrating output signal obtained with the repetitive scanning of the spot 15d. Thus, when the position of the beam spot 15 is within the said range, light emitting diodes 11, 12 are put out at all times.

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.

In laser beam printers, reading devices, and the like, a laser beam that forms a beam spot on a surface to be scanned, such as a candy, a needle surface, or a reading surface, is deflected and controlled, and the surface to be scanned is scanned with the beam spot. In the printer, the beam spot is adjusted to match the timing of modulating the laser beam and the beam spot position using the first record information, and in the reader, to match the beam spot position and the operation timing of the photoelectric conversion means. Scan start detection should be 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 when the amount of positional deviation in the direction perpendicular to the scanning direction of the fi'π laser beam becomes large. This phenomenon will be explained with reference to FIG.

When the beam spot 2a is scanned over a photoelectric conversion element such as a photodiode having a rectangular light-receiving surface lac& as shown in Fig. 1(a), the detection output signal of the photoelectric conversion element 1 is as shown in Fig. 1(b). Characteristic A is obtained. On the other hand, the detection output signal of the photoelectric conversion element 1 has characteristic B when the beam spot 2b is scanned. These output signals A and B are
If the presence/absence is judged using the threshold value
The start of scanning (characteristic B) cannot be detected. Also, if the presence/absence is determined using a threshold value vthl that is smaller than this,
Although the start of scanning of the beam spot 2b can also be detected, a detection error of Δt occurs with respect to the detection of the start of scanning of the beam spot 2a. Moreover, by reducing the threshold value, in order to eliminate the influence of noise and problems caused by misalignment of the light-receiving surface of the photoelectric conversion element and the beam spot in the perpendicular direction, a synchroscope is used during assembly and maintenance to detect the photoelectric conversion element. The output signal was observed and relative position adjustment work was carried out. However, there is the hassle of requiring measuring equipment, and the VC has the considerable drawback of detecting misalignment conditions 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, the light receiving surfaces 3a, 3b, 5w, as shown in FIG.
A photoelectric conversion element for detecting scanning position deviation is provided, and the magnitude of the output signal obtained from this photoelectric conversion element is compared.
It is conceivable to detect the amount of deviation based on 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 detection signals of both photoelectric conversion elements have the same amplitude. If the beam spot scanning position deviates from tilting in the perpendicular direction, a difference in the strength of the detection signal will occur. By arranging these so that the magnitudes of the detection signals are equal and observing the magnitude and polarity during operation, the amount and direction of deviation in the scanning position of the beam spot can be detected.

However, even in this case, the laser beam light intensity may be biased or
If there is a difference in photoelectric conversion characteristics between two photoelectric conversion elements, a positional deviation detection error will occur, making it difficult to prevent the above-mentioned problems from occurring.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a laser beam scanning system that
An object of the present invention is to provide a beam position detection device Rk capable of reliably detecting a scanning position shift in a direction perpendicular to a laser beam scanning direction during operation of a scanning system.

[Summary of the invention]

In order to achieve this object, the present invention provides that the eleventh point in the laser beam scanning direction is at a position f? in a direction perpendicular to this scanning direction. A detection output signal having a time width corresponding to the front perpendicular direction position vK of laser beam scanning is obtained by a photoelectric conversion means W having a light receiving surface that sequentially changes according to π and disposing this light receiving surface in the deflection scanning optical path of the laser beam. This output signal is compared with a reference value by a comparison circuit means to detect the amount of deviation from the reference position, and by using the time width of the detection output signal as a position detection element, the photoelectric conversion means can be used. Variations in photoelectric conversion characteristics and beam spot light intensity? This is to reduce the detection error due to k.

[Embodiments of the invention]

Figures 3 to 5 show one embodiment of the present invention.
The figure is an electric circuit diagram, FIG. 4 is a light-receiving surface of a photoelectric conversion element and a detection signal waveform diagram, and FIG. 5 is a scanning position deviation detection characteristic diagram.

In FIG. 3, the photoelectric conversion element 5 is connected between the H input terminal of the operational amplifier 6 and the square source (-■), and the (+l input terminal of the operational amplifier 6 is grounded. The (+ input terminal of the comparator 7 is 6, and the (→input terminal is connected to the threshold power supply (10 V, ) π.Integrator circuit 8
is composed of an operational amplifier 8a, a resistor 8b, and a capacitor 8c. Operational amplifier 8a (→input terminal is comparator 7
(a) 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 front light distribution electric conversion element 5 is within a predetermined range of the light receiving surface. (1) input terminal is connected to the output terminal of the integrating circuit 8, and the comparator 9
The range setting power supply (-V.1) is connected to the (-)1 input terminal of the
The range setting power supply (V
, 2) are connected to each other. 11 and 12 are light emitting diodes, which are connected to each output terminal of comparators 9 and 10 and the positive power supply (
+V) respectively. The window type comparator 13 determines the limit of the positional shift amount 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(
→The input terminal is connected to the output terminal of the integrating circuit 8, and the (4) input terminal of the comparator 13a is the limit setting power supply.
r s t 1 ) p Cossiparator 13b (a)
A limit setting power supply (-rsfz) is connected to the input terminal. Then, the output terminal of the comparator 13b and the positive power supply (+
(2) A light emitting diode 14 should be connected between the two. A scanning start detection reference signal V 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. 4(a) VC. The comparator 7 has a light receiving surface 5a whose width in the direction is sequentially determined by the scanning position f.
As shown in FIG. 4(b), the output signal ■, of the scanning position of the beam spot 15a (V6.
By repeatedly scanning the scanning position of the beam spot 15b, V,
b. Old... Tonaro. When this output signal V is integrated by the integrating circuit 8, an integrated output signal V is obtained. varies depending on the scanning position #, as shown in FIG. 5(a) vc. beam spot 15
The scanning position of c is the center and the beam position is 15b.

15d, the range setting power supply (', i
) and set the range setting power source (-V, z)%7 to a voltage equal to (integrated output signal -vI obtained by repeated scanning) dVC of the beam spot 15d. This results in
As shown in FIG. 5(b), when the beam spot 15 repeatedly scans between the beam spots 15b and 15a at π, the two comparators 9. The output of lO is at a high level, and the light emitting diodes 11 and 12 are both turned off. Then, the scanning position of beam spot 15 is further from this range)
The output of the ff-f comparator 9 on the lsa side becomes a low level and the light emitting diode 11 lights up, and conversely, if it shifts to the beam sub-15e side, the output of the comparator 10 becomes a low level and the light emitting diode 12 lights up. . Therefore, the scanning position 1 of the beam spot 15 can be adjusted by turning off both light emitting diodes (11 and 12).

Furthermore, the limit of the scanning position at which the photoelectric conversion element 5 can detect the scanning of the beam spot 15 is the beam spot (15a, 15).
Assuming that the scanning position is e, the integrated output signal -■ obtained by repeatedly scanning the beam spot 15a. , set the limit setting power supply (-■, .fl) to a voltage equal to ,
Integral output signal -■ obtained by repeatedly scanning the beam spot 15e. , set the limit power supply to a voltage equal to (−
Vreft), when the scanning position of the beam spot 15 is within the range of the beam spots 15a and 15e and the photoelectric conversion element 5 detects the scanning, the output of the comparator 13 becomes a 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 on the basis of the rise of the output signal Vga of the comparator 7.

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

(a) It is possible to observe and carry out adjustment work without using a measuring device in which the scanning position of the light-receiving surface of the photoelectric conversion element and the beam spot is misaligned.

(b) Since the amount of scanning position shift is detected according to the time width of the detection direction of the photoelectric conversion element, it is not easily affected by changes in the light intensity of the laser beam spot or the sensitivity of the photoelectric 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.

The second embodiment shown in FIG. 6 adds a second photoelectric conversion element 16 to the first embodiment explained in FIG.
The detected output signal of the photoelectric conversion element 16 is amplified by the operational amplifier 17, further waveform-shaped by the comparator 18 to obtain an output signal with the opposite polarity to the output signal of the comparator 7, and the output signals of both comparators 7 and 18 are amplified by the integrating circuit 8. It is designed to be integrated.

In this second embodiment, as shown in FIG. 7(a), the light receiving surface 16a of the second photoelectric conversion element 16 is parallel to the terminal edge of the light receiving surface 5a of the first photoelectric conversion element 5. If the starting edge is inclined as shown in FIG. .18 output signal child v
1°-v, it Fig. 7(b) (7) +V, , ~-V
, , Nox 5K. Both output signals are 10 V.
-V, is integrated by the integrating circuit 8 to obtain an integrated output signal V. changes depending on the scanning position as shown in FIG. 8(a). At the repeated scanning position by the beam spot 15c, the output signal +Vmc of the comparator 7 and the comparator 1
Since the time width of the output signal -Vse of 8 is equal, the integral output signal V. becomes zero, and beam spots 15a, 15b
In the repeated scanning of beam spots 15d and 15e, the integral output signal v0 is positive, and in the repeated scanning of beam spots 15d and 15e, the integral output signal V0 is positive.
. becomes negative. Therefore, the range setting power supply (+V, 1), (
V-2) respectively, and the integral output signal vOb e '0
Set the voltage equal to 4 and set the limit power supply "■r*tt
L (-vr s f 2 ) respectively as an integral output signal +VOae-V. . If the voltage is set equal to , the same result as above can be obtained. Furthermore, 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. In addition, the output time width of the comparator 7.18 changes in the opposite characteristic according to the change in the scanning position of the beam spot 15, so the change in the integral output signal v0 becomes large, and the detection accuracy becomes high (
Become.

Further, in this second embodiment, the output signal of the comparator 18 -
The falling edge of vo can also be used as a reference signal for scanning start detection.

Furthermore, the same effect can be obtained even if the light-receiving surfaces 5a and 16a of the photoelectric conversion elements 5 and 16 have their starting edges and ending edges reversed, respectively. 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. Photoelectric conversion element 5
is connected between the (A) 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, -The input terminal is connected to the threshold power supply (+V*h).

Enable input terminal Bnab of digital counter 19
je is connected to the output terminal of the comparator 7, a clock signal CLOCK is applied to the clock input terminal ck,
A clear signal CLEAR output from the delay circuit 20 is applied to the clear input terminal C1ear. counter 1
The count output signal output from the latch circuit 2 is triggered by the trigger signal TRIGER from the delay circuit 20.
The latched value is latched at 1, and the latched value is applied to the digital comparator 22 as a comparison value n.

The output signal V of the comparator 7 enables the counter 19 and is used as a scan start detection reference signal, and is further input to the delay circuit 20 to latch the output of the counter 19 every scan.
This serves as a reference for generating the clear signal CLEAR that generates BR and then clears the counter 19. The comparator 22 receives the output signal DI! of the latch circuit 21! l
and the reference value Dr,i, and the comparison output signal is sent to the light emitting diodes 26, 24, and 25 via inverters 23, 24, and
Given on 27.28.

In the above circuit configuration, the photoelectric conversion element 5 is
When the light receiving surface 5a is shown in FIG.
When the center scanning position of the beam spot 15c is scanned, an output signal V is generated from the comparator 7 as shown in FIG. Ru. When the output signal V disappears, the delay circuit 20 generates the trigger signal TRIGERI- with a time delay of tdl, and at its rising edge, the latch circuit 2 generates the count output signal of the counter 19.
Latch to 1. Thereafter, a clear signal CLEAR is generated with a further delay of td2, and the counter 19 is cleared.

The count output signal at this time, that is, the comparator 22
When the comparison value Dlts given to is Dine, the reference value is 1. , as Dr, ,=Di,. If so, the light emitting diode 27 can be turned on. When the beam spot 15b scans the light receiving surface 5a, the comparison value DIn becomes Dl s b and DImb<Drsf
Therefore, when the light emitting diode 26 lights up and the beam switch 15d scans the light receiving surface 5a+Ir, the comparison value DI becomes DI! l d becomes DI+ad>Drs
f, so the light emitting diode 28 lights up.

The fourth embodiment shown in FIGS. 11 and 12 is shown in FIGS.
This is an example in which the signal processing is digitized using a VC and two photoelectric conversion elements of 5.16 VC as in the second embodiment shown in the figure. The photoelectric conversion elements 5゜16 are each connected between the (1) input terminal of the operational amplifier 6.17 and the positive power supply (+■), and the (→input terminal of each operational amplifier 6.17 is grounded. Each (1) input terminal of is connected to the output terminal of the operational amplifier 6.17, respectively,
Each input terminal is connected to a threshold power supply (+Vth).

The output signal V, □ 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. Output signal of comparator 18■
1□ is input to the delay circuit 20 and also to the input terminal of the NAND gate 30. Each NAND game) 29,
A clock signal CLOCK is input to the other input terminal of 30.

The digital up/down counter 31 has an up count input terminal Up connected to the output terminal of the NAND gate 29, a down count input terminal Down connected to the output terminal of the NAND gate 30, and a data input terminal Data.
The initial value DATA is applied to VC, and this initial value DATA
is taken into the counter 31 by the load signal LOAD applied from the delay circuit 20 to the load input terminal Load. The count output signal output from the output terminal Q of the counter 31 is the trigger signal TRI from the delay circuit 20.
It is latched by a latch circuit 21 triggered by GER, and the latched value is applied to a digital comparator 22 as a comparison value. The comparator 22 converts the output signal DI n of the latch circuit 21 into a reference value D r * f
The comparison output signal is output from inverters 23 and 2.
4.25 to the light emitting diodes 26, 27.28.

In the above circuit configuration, when the photoelectric conversion element 5.16 is the light receiving surface 5a, 16a shown in FIG. 12(a),
When the beam spot 15c scans the center scanning position of the light receiving surfaces 5a and 16a, the light receiving surface 5a is first scanned and the output signal v,1 of the comparator 7 is generated, so that the clock signal CLOCK is increased and decreased via the NAND gate 29. It is applied to the up-count input terminal Up of the counter 31, and counts up by the number Jl of the clock signal CLOCK while the output signals 1 and 1 are being generated.

Next, the light receiving surface 16a is scanned and the output signal vs2 of the comparator 18 is generated, so that the clock signal CLOCK is sent to the up/down counter 31 via the NAND gate
The clock signal CL is applied to the down count input terminal of
Count down by the number of OCKs Nc2. When the output signal V, □ of the comparator 18 disappears, the delay circuit 20
The trigger signal TRIGBR is generated due to the time delay of the td process, and the count output signal of the counter 31 is latched into the latch circuit 21 at the rising edge of the trigger signal TRIGBR. Thereafter, a load signal LOAD is generated with a further delay of td2, and the initial value DATA is taken into the counter 31. As a result, the latch circuit 21
output signal, that is, the comparison value Di! input to the comparator 22. l is N for scanning at the center scanning position, ,=Nc2
Therefore, D! l=DATA. Therefore, the reference value of the comparator 22 is 7. , becomes,,,==
If it is set as DATA, the light emitting diode 27 can be turned on. When the beam spot 15b scans the light receiving surfaces 5a and 16a, the comparison value D1m is DI
Since m b becomes DIn, <Dr, f, the light emitting diode 26 lights up, and when the beam spot 15d scans the light receiving surfaces 5a and 16g, the comparison value DIn becomes the beam 61. Since Dt tra > Dr e t , the light emitting diode 28 lights up.

The third point mentioned above. The fourth embodiment is also the same as the first embodiment. It can be modified and implemented in the same manner as the second embodiment, and the same effects can be obtained.

In each of the above four embodiments, the photoelectric conversion element 5.16 is 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, and may be stepped.

〔Effect of the invention〕

As described above, according to the present invention, scanning of a beam spot is detected by a photoelectric conversion means having a light receiving surface whose width in a laser beam scanning direction changes sequentially according to a position perpendicular to the scanning direction, and the scanning time is Since the scanning position shift amount with respect to the reference position is detected based on the width, there is an effect that detection errors due to variations in the photoelectric conversion characteristics of the photoelectric conversion means and the beam spot light amount can be reduced.

[Brief explanation of the drawing]

Figure 1 (a), (b) &i: Beam spot scanning and output characteristic diagrams for the light receiving surface of the photoelectric conversion means; Figure 2 is a light receiving surface and beam spot scanning diagram of the improved photoelectric conversion means; Figures 3 to 3; FIG. 12 shows an embodiment of the present invention, FIG. 3 is an electric circuit diagram of the first embodiment, and FIG. 4(a). (bl is the beam spot scanning and output characteristic diagram for the light receiving surface of the photoelectric conversion means, Fig. 5 (a) to (c) k"L
6 is an electric circuit diagram of the second embodiment, FIGS. 7(a) and 7(b) are beam spot scanning and output characteristics diagrams for the light receiving surface of the photoelectric conversion means, and FIG. 8 is a diagram of its position detection characteristics. f
a) to (C) are position detection characteristic diagrams, FIG. 9 is an electric circuit diagram of the third embodiment, and FIGS. 10 (a) and (b) are position detection 5...photoelectric conversion. Element, 5a... Light receiving surface, 8... Integrating circuit, 9, 10, 13...
···comparator. Figure 1 Figure 2 n D Figure 7 JP-A-59-70359 (9) Figure 8 +r'-b scanning value! Mu

Claims (1)

[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 position where the width of the laser beam in the scanning direction is perpendicular to the scanning direction. A photoelectric conversion means has a light-receiving surface that changes sequentially according to the laser beam, and the light-receiving surface is placed in the deflection scanning optical path of the laser beam, and a photoelectric conversion output signal obtained from this photoelectric conversion means is compared with a reference signal to receive light. Comparison circuit means for detecting the relationship between the time width of the beam spot scanning the surface and the reference time width is provided, and the scanning position in the perpendicular direction of the beam spot scanning the light receiving surface is provided based on the output signal of the comparison circuit means. A beam position detection device for a laser beam scanning system characterized by detecting deviation. 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 for a laser beam scanning system, comprising: 3. In claim 1, the front light distribution electric conversion means are arranged side by side in the scanning direction, have the same width in the scanning direction at the reference position in the orthogonal direction, and have opposite width change characteristics depending on the position in the orthogonal direction. The comparison circuit means is a waveform shaping circuit that shapes the output signals obtained from the two photoelectric conversion elements so that the two output signals have opposite polarities. , an integrating circuit that integrates these two output signals of opposite polarity and outputs the difference thereof, and a discrimination circuit that discriminates the relationship between the magnitude of the output signal of the integrating circuit and the magnitude of the reference signal. A beam position detection device for a 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 determination that determines the relationship between the counted value of this counter and a reference value. A laser beam scanning system beam position detection device characterized by being equipped with a circuit. 5. In claim 1, the photoelectric conversion means are arranged side by side in the scanning direction, have equal widths in the scanning direction at the reference positions in the orthogonal direction, and have width change characteristics corresponding to the positions in the orthogonal direction. Two photoelectric conversion elements having opposite light-receiving surfaces are provided, and the comparison circuit means counts up the f clock pulse while the output signal of one photoelectric conversion element is present, and the output signal of the other photoelectric conversion element is present. 1. A beam position detecting device for a laser beam scanning system, comprising: an up/down counter that counts down clock pulses during a period of time; and a determination circuit that determines the relationship between the counted value of the up/down counter and a reference value.