JPS59229970A - Light beam scanner - Google Patents

Abstract

PURPOSE:To obtain a light beam scanner which is easily manufactured and adjusted with good productivity by polarizing and correcting a light beam optically on the basis of deviation so that unevenness of the scanning of a light beam spot is eliminated. CONSTITUTION:A reflecting surface 8 of a rotating polygon mirror 1 is irradiated with a parallel incident laser beam 4 from a laser light source through an optical deflector 5 as a correcting means. The reflected beam from the reflecting surface 8 is converged by a convergent lens 2 such as an ftheta lens into a convergent laser beam 6, which forms an image on a surface 3 to be scanned. When the mirror 1 rotates clockwise as shown by an arrow, the laser beam 6 scans on a photoelectric detector 7 before striking the surface 3 to be scanned for every scan. The correcting means includes the optical deflector 5, a piezoelectric element driving part 9 which drives it, and a signal processing unit 10, which controls the driving part 9 on the basis of the amount of deviation detected by the detector 7 to control the amount of displacement of the deflector 5.

Description

[Detailed description of the invention]

The present invention relates to a C-beam scanning device using a rotating polygon mirror, and in particular to an improved light beam that prevents deviation of the light beam in a direction intersecting the scanning direction on each reflecting surface on the surface to be scanned. The present invention relates to a scanning device. The original beam scanning device using a rotating polygon mirror has fθ
In combination with an imaging optical system such as a lens, it is used as a scanning means to move a laser spot, etc. linearly at a constant speed on a plane, and the ratio of the total scanning length to the diameter of the laser spot is 71.
It is known to be useful because it can be obtained with a value of 0.04 or higher. By repeatedly moving the laser sporatra at high speed using such a rotating polygon mirror, linear scanning is performed in the horizontal direction, and by using a slower scanning means in the vertical direction, two-dimensional raster scanning is performed in both directions. I'll do it. In this case, if the angle formed between the reflective surface of the rotating polygon mirror and the rotation axis is different for each reflective surface of the polygon mirror due to manufacturing precision, etc., the angle formed by the rotation axis of the rotating polygon mirror may be This results in scanning unevenness 7. As a method for eliminating the scanning unevenness, for example, Japanese Patent Application Laid-Open No. 54-7
Publication No. 0846 discloses a system in which a light beam from a light source is corrected and deflected in a direction crossing the scanning direction in front of a reflecting surface of a polygon mirror that contributes to scanning using an optical deflector 7 such as a galvanometer mirror. There is. According to this method, even when performing high-resolution and high-precision scanning, it is possible to reduce scanning unevenness without causing variations in the diameter or shape of the scanning light spot. The error 'ze feJ is set to 611' with high accuracy, and this is artificially written into the storage medium, and the optical deflection is applied to the read value from the storage medium in synchronization with the rotation of the polygon mirror. It is necessary to operate the device so that the deflection angle of the device corresponds with high precision, and conventionally, it takes a lot of time and effort to adjust the deflection angle of the device. I needed to use something. SUMMARY OF THE INVENTION The main object of the present invention is to overcome the disadvantages of the conventional ones and to provide a scanning unevenness correcting optical beam scanning device which is easy to manufacture and adjust and has good productivity. Another object of the present invention is to measure scanning unevenness with a simple configuration, and to simultaneously extract a trigger signal indicating that the light beam spot has reached a specific position in the main scanning direction. That's true. A light beam scanning device according to the present invention to achieve such an object has a basic configuration that moves the light beam in one predetermined direction in order to linearly scan a scanning surface with a spot of the light beam. a main scanning means; a pair of photoelectric elements for detecting deviation that output substantially equal photoelectric signals upon being irradiated with the light beam when the spot of the light beam is on a predetermined scanning trajectory; When scanning with a spot, the light beam is irradiated 7 temporally earlier than the photoelectric element for detecting deviation.
a timing photoelectric element arranged to receive the light beam and determining the timing at which the light beam irradiates the deviation detection light quantity element; and a timing photoelectric element arranged to receive the light beam; a deviation detection means for detecting the amount of deviation of the light beam spot from the predetermined scanning trajectory from both photoelectric signals; a correction means for optically correcting the deflection of the original beam based on the amount of deviation so as to eliminate scanning unevenness of the light beam spot due to Two photoelectric elements are arranged one after the other on the predetermined scanning trajectory, and each of the four photoelectric elements, these two timing photoelectric elements and the pair of deviation detection photoelectric elements, is placed on the scanning surface at the predetermined position. Preferably, one 4-element photoelectric detector having these four photoelectric elements as elements is used. In this case, the deviation detecting means specifically (hereinafter referred to as G-1)
a first subtraction means for obtaining a difference value between both photoelectric signals of the pair of shift detection photoelectric elements; 0!2 subtraction means for obtaining a difference value between both photoelectric signals of the two timing photoelectric elements; and the timing. While the photoelectric element for use is being irradiated with a light beam, the difference value h'' obtained by the second subtraction means - the predetermined dead zone width becomes substantially zero, and the difference obtained by the first subtraction means is calculated by the first subtraction means. The details of the present invention will be explained below along with the drawings of the embodiments. This is a layout diagram structurally showing the configuration, in which a parallel incident laser beam ( 4) is irradiated through the optical deflector (5), which is a correction means, and the reflected beam from the reflecting surface (8) is condensed into a laser beam by a focusing lens (2) such as an f-theta lens.

[6], so that the image is formed on the scanning surface (6). (The force is placed in front of the effective scanning area on the scanning trajectory of the short hole surface (6) When the polygon mirror (1) rotates clockwise as shown by the arrow in the figure, the condensed laser beam (6) moves across the scanning surface ( 6)・\This photoelectric detector f before entering
Figure 1 shows the moment when the condensed laser beam (61#''-) is incident on this detector (7), and the voricon mirror (1) is further scanned. When it rotates, the condensed laser beam (6) C horizontally scans the surface (6) as shown in Figure 2 (up and down in the drawing).The correction means is an optical deflector (5). , the piezoelectric roller b part (9) that drives the two light deflectors, and the part ψU in FIG. 4, which will be described later.
signal processing unit with the circuit configuration shown) (10
), and this unit) (10) controls the drive unit (9) based on the amount of deviation detected by the force of the photoelectric detector (force) and controls the amount of deflection of the light deflector (5). The light 'a detector (7) is a condensed laser beam (6)
The position of the spot of the beam (6) in a direction perpendicular to the scanning direction (in the drawing, the front and back directions of the paper surface) is detected with respect to a predetermined scanning trajectory of the spot of the beam (6) on the scanning surface (6). An example of (n) is as shown in the sixth factor. ) evenly divides the circle into 4
A pair of photoelectric confections for detecting deviation ( 7A) (7C) are arranged facing each other with the track (61) in between, and another pair of timing photoelectric elements (7B) (7D) are arranged on the above-mentioned shape -1n (61). Choose these photoelectric elements (7A) (7B) (7C)
(7D) are arranged one by one in the four quadrants of the orthogonal coordinates whose origin is located on the scanning trajectory (61) on the scanning plane (3), and when there is no scanning deviation, the Photoelectric element - R7A) (spot approximately the center of the border of (7C))
(60) is made to pass. These four photoelectric elements (7A) (713) (7C) (7
D) output (70A) (70B) (70C) (70D)
are extracted separately and sent to the signal processing unit (described later) (
10), the beam spot (60) is used for timing protrusion in order to start drawing the beam spot (60) in a predetermined scanning direction, detecting the amount of deviation in the direction perpendicular to the scanning direction, and monitoring the laser beam power. FIG. 4 shows a specific example of the structure of the above-mentioned unit (10).
Includes tatami processing system, blood protection means, and part of combat means 6 (IolA) (101B) (101C)
(IOID) are input terminals 4) and (101A
) is the output signal (7OA) of the optical separator (7A), and (I
OlB)) This is how the photoelectric element (7B) comes out 4. - issue (70
B), (101C) is the output signal of the photoelectric element (7C), and (101D) is the output signal of the photoelectric element (7D) 7Q.
D) are each input. (102) can input 1'' from child (101A) (101C) to signal (70A)
The output 10 of this differential circuit (102) is input to a sample and hold circuit (103), which is a monostable multipipe 1/- to be described later. The amplitude 61H value is sampled and held at the timing of the output pulse of the data generator (115). The output of the sample and hold circuit (103) is given to one input of a divider (104). The signals (7 [IB) (70D) given to the other input terminals 1 (101B) and (101D) are input to the adder circuit (110) to obtain the addition output (4), and the signal (11, 2) to obtain the difference output fk+.The output of the adder circuit (110) is input to the comparator (111) and the preset comparison voltage IE(
When the output of the adder circuit (110) exceeds the comparison target (Erz) 'a', the comparator (1
The output of 11) is on a world-class level. Also, the output of the differential circuit (112) is connected to another comparator (11
3) and is compared with the zero level by this comparator (113), and only when the output of the differential circuit (112) exceeds the zero level, the output voltage l'T of the comparator (113)
]ll level. The outputs of the comparators (ili) and (F 13 ) are input to an AND circuit (114), and the AND circuit (114) sets the output level to 1 when both inputs are at the 1 peak level. The monostable multivibrator (115) is triggered when the output of the AND circuit (114) falls from the sun to the moon, and then produces an output for a preset period of time. (11
The output pulse of 5) is the spot scanning synchronization signal (125)
It is output from the signal processing unit (10) and is used as a sample and hold command signal for the sample and hold circuit (103), and is also used as a sample and hold command signal for the sample and hold circuit (116).
'r to the cross section signal of the nonΦ converter (105), which will be described later.
Furthermore, it is used as a shift pulse of a shift register (106), which will be described later, via another delay circuit (117) 7. The output signal of the photoelectric element (7B) at the leading position as shown in FIG. 6 with respect to the main scanning direction of Spora (60) is
In the example shown in Figure 7P and 4, the input terminal (101B) is input to another comparator (107) and a sample hold circuit (,109),
Another reference voltage aE (Er1) set in advance in 07)
When it exceeds (Er1), another monostable multivibrator (108) l: triggers, and this 1￥L signal ( The amplitude value of 70B) is held by the sample and hold circuit (1[]9). This sample hold is performed to accurately measure the power of the light beam by determining the value of the photoelectric signal output (70B) when the spora (60) is completely placed on the photoelectric element (7B). be. The output of the sample and hold circuit (109) is sent to the divider (10
4), and the divider (104) outputs the sample hole toy direct (il) of the differential circuit (1).
The quotient (elp) of el and the sample hold value ip+ of the output (70B) of the photoelectric shift register (106)
ノ＼It is inputted to 5. The shift register (106) has 8 as shown in FIG.
The digital signal set in parallel to the input can be shifted up to 8 steps corresponding to the octahedral polygon mirror (1) with two reflective surfaces, and the synchronization signal for data shift is Multivibrator (115)
The output pulses of the delay circuits (116) (117)19. c.
A signal delayed by a predetermined period of time is used as a clock. (119) and (120) are latch circuits that respectively latch input digital amounts in accordance with timing pulses. On the other hand, the Noratch circuit (119) is connected to the first shift register (1
The other latch circuit (120) latches the digital signal from the final stage (8th stage) of the second shift register (121) of another 8 stages, and The timing pulse for controlling the latch timing of the latch circuits (119) and (120) is supplied to the terminal (1
18). This timing pulse is generated at the time when the beam (60) reaches the end point of the effective scanning range for the scanning surface (6) in each scanning period due to the rotation of the polygon mirror (1), that is, at the end of the effective scanning time of each scanning period. Therefore, the timing pulse given to the terminal (118) can be one obtained by multiplying the output pulse of the monostable multivibrator (115) by a short delay during the effective scanning time, or ) effective scanning end point ζ different light ′I
Signals obtained by arranging an IL detector and shaping its photoelectric output can be used in various ways. (122) is a subtracter, which subtracts the output of the latch circuit (i19) from the output of the latch circuit (120) and outputs the result. The second shift register (121) has eight parallel stages similar to the first shift register (106), and has a subtracter (
The output of 122) is inputted as actual data, and the same as the first shift register (106) is input to the delay circuit (117).
The shift is controlled by the output of. The output of the subtracter (122) is sent to the digital-to-analog converter (
123) and is converted into an analog signal output (124), and this analog signal output (124) serves as a voltage converter that drives the piezo drive element of the optical deflector (5) shown in FIG. (9) I\\ will be able to input a large amount. Now, the operation of the original beam scanning device having the configuration shown in FIGS. 1 to 4 at 1:5 will be explained in conjunction with FIGS. 5, 6, and 7 as follows. First, we will describe the detection of the deviation of the beam robot from the predetermined scanning trajectory by the photoelectric detector (7).
In FIG. 1, the beam (6) reflected by the rotation of the Bonn mirror (1) on its reflective surface (8) and focused by the focusing lens scans the photoelectric detector (force) at the beginning of the scan. Assuming that the beam (60) moves from left to right in Fig. 6 and the scanning locus matches the foot trajectory that passes through the center of the boundary between the photosensitive elements (7A) and (7C), the photoelectric element ( 7A] and (7c). The phase (i+) of the output of the photoelectric element (7B) and (7c) will show a change over time like the waveforms (A, -c) in Figure 5. At time t0 at the boundary of the photoelectric element (7C), the beam spot (60) crosses the photoelectric element (7C)
If it is close to A), the difference (e) in the output of the pixel element will be positive, and conversely the difference between the beam spot (60)l] - photoelectric element (7A)
If it is closer than (7c)t, the output difference fe) is negative, and the output difference tel is compared to the power of (60), so the light beam (1) is a light whose power changes. In this beam scanning device, this output difference tel is corrected by the magnitude of the beam power, and the beam scanning is performed without depending on the magnitude of the beam power.
) in the direction perpendicular to the scanning direction. For this purpose, a photoelectric element (7B
) waveform of the output signal (70B) + maximum value of jl (p
) Use fzt. This maximum value (p) is determined as follows. signal(
70B)'? : The comparator (107) compares the comparison level (Er1.) with the comparison level (Er1.) at the time t when the signal (70B) becomes sharp, the comparator (107) operates, and the pulse width of the monostable multivibrator (108)
At time t3 delayed by τl), the value of the signal (70B) is held as a sample, and the maximum value fp) is obtained as the hold output. The divider (104) outputs (e/p), which is an amount that does not depend on the beam power. On the other hand, in order to detect the position synchronization of the beam spot (+!S[]) in the scanning direction, the waveform CB-1))'& in Fig. 5 is used, and the falling edge of the signal (70B) and the signal (701)) are used. Time t from the zero point of the waveform (B-D) at startup. seek. The signal processing unit (io) uses the zero point of the waveform CB-D) between times t3 and t4, when the waveform CB+D) becomes higher than the reference level (Era). Note that the deviation angle θ of the beam (6) in the direction perpendicular to the scanning direction of the rotating polygon mirror (1) and the detected deviation (
As shown in Figure 6, the relationship with e/p) is almost linear in the range where θ is not very large near the origin, and is linear in the correction range of the actual deviation angle θ. In the usage state of the 80-rotation polygon mirror (1), each reflective surface of the polygon mirror (η is used to contribute to scanning sequentially, but for each reflective surface, the beam (6 ), the center contributes effectively to scanning for about half of the time, and the remaining half of the time cannot normally be used for scanning. Figure 7 corresponds to the rotation of the rotating polygon mirror (1). 2 is a timing chart of the deflection correction operation, in which (a) shows the effective scanning time of each of the eight reflecting surfaces (Fl) (Fz) (Fa
) (F4XFsXFaXFyXFa), (bJ is the timing of detecting the amount of deviation, (C) is the launch timing by the timing pulse to the terminal (118), (d) is the deflection of each reflecting surface. The correction time is (T(t)(F2)(Hs)(Tom)(F
5) Timing pulses of the deflection correction operation shown in (H6) ()17) ()J8) are shown. For example, as shown in FIG. 7, during scanning with the first reflecting surface, the amount of deviation is detected at the time ((3+)) when the spot is outside the scanning range before the scanning effective time (Fl), The shift amount detection point (G
1) During the previous time (Hl), the optical deflector (5) corrects the deflection. After the effective scanning by the first reflecting surface is completed, the next shift scene is detected in the same way at time (G2), and the deflection correction is performed based on the previous shift amount during time (F2), and the following steps are performed. The same is true. In this case, the deflection correction amount corresponding to each reflective surface is corrected not only based on the deviation amount of the previous detection result, but also based on the actual value of past corrections before that rotation and one rotation before that. , after a large number of rotations, very high precision deflection correction is automatically achieved. After the time (G1) shown in FIG. 7 (bJ), the output pulse of the monostable multivibrator (115) appears in FIG. (116), the output (e/p) of the divider 3γ5 (104) is converted into a digital quantity, and the amount of deviation as a digital signal is determined by the first shift register (106) at the output timing of the delay circuit (117). ) is stored in the first stage of the first rotation of the mirror.
It will be expressed as (xe2) for the reflective surface and (nem) for the m-th reflective surface at the n-th rotation. Thread '76 (1e work) is stored in the first stage of the shift register (106).
06) No. 2.3, 4, 5, 6, 7, 8 U
In the Z-th position, the deviation Q of each reflective surface during the previous rotation is shown (
oes) (oey) (oeg) (oes) (oe4) (
oem) (Oe2) is stored in the body, and the latch circuit (ii5') is loaded with the amount of deviation (.G4) with respect to the first reflecting surface exactly one rotation before. The second shift register (121) has a digital-to-analog converter (123)
A digital amount of the amount of deviation given to the drive unit (9) via the drive unit (9) is stored, and if the amount of deviation of this digital value is similarly expressed as (num), then the second shift register (
121), at present, (lul) (O
F8) (OF7) (6u6) (olla) (ou4) (
ousHollz) is set to 6, and the latch circuit (
120), the deviation 1J (oul) with respect to the first reflecting surface just one rotation ago is latched. The subtractor (122) is therefore (out oel)=(s
ut], which is calculated as the effective scanning time (Fl
) is maintained until the end of the period. It goes without saying that the output (5lit) of this subtracter (122) is stored in the first stage of the second shift register (121). The contents of the latch circuits (119) and (120) change depending on the timing pulse applied to the set C terminal (118) at the end point (El) of the effective scanning time (E'x), and the contents of the launch circuit (119) change. becomes (Oe2) - content b of the launch circuit (120) - (6u2). As a result, the subtractor (122) is (1u2)=(.F2-0e2
), and this output (1u2) is the second
The effective scanning time (F
During the deflection correction time (F2) before the start of 2), the drive unit f91
Deflection of light deflection amount (5) by '? It! Used for positive operation. The contents of the first shift register (106) at this moment are from the input stage to I'm (tex) (oes) (oa7) (oe
6) (oes) (oe4) (oem) (Oe2) - Also, the contents of the 8-bit 2 shift register (121) are (1111) (0118) (OF7) (OF
6) (Ou5χ0u4) ((, F3) (OF2 ), which has not changed yet. Next, at time (G2), the above-mentioned split $4 device (104)
The amount of deviation (1e2) from the second reflecting surface from It is stored in the input stage of the register (106), and the second shift register (121) is also shifted at the same time.Of course, the delay time of the delay circuit (117) is the same as that of the sample and hold circuit (103), the divider (104), and the analog・It goes without saying that it is set to a longer time than the sum of the operating times of the digital converter (105).Now, after this point (G2), the 4-device 1 shift register (106)
The contents of are (1e2) (lel) (Oe8) in order from the input stage.
)(Oe7)(Oe6)(0(!5)(Oe4)(Oe
3), and the contents of the second shift register (121) are (1u2) (sut) (ous) in order from the input stage.
(OH7) (oua) (OH2) (OH4)
(o113) n In this way, the deviation m (tez) and the deflection correction ffl (tug) with respect to the second reflecting surface are
is stored, and the detection of the positive deflection 111 and the amount of deviation are repeated for each reflecting surface of the polygon mirror (1) in the same manner. After the polygon mirror (1) rotates once in a row (G'l
), the amount of deviation (,2e1) of the second rotating moon with respect to the first reflecting surface from the divider (104) is converted into a digital signal and then sent to the first shift register (10j6).
The second shift register (121) is also shifted at the same time. The first shift register (106) at this time
The contents of are (2el) (les) in order from the input stage.
(1e7) (tea) (les) (ze4)
Similarly, the contents of the second shift register (121) are (+ut) (1ug
) (zu7) (rus) (5ols) (tu<
3 (tug) (1112). The launch circuit (119) latches (, e, )'la:, the latch circuit (120) G'l (tut), and the subtracter (122)
), that is, the deflection correction amount for the first reflecting surface of the second rotation continues to be output. In this state, effective scanning of the beam by the first reflecting surface of the second rotation is performed, and when the end time <E', the content of the latch circuit (119) becomes (1e2), and the content of the latch circuit (120) becomes (1e2). is (1
u2) respectively, and the subtracter (122) changes to (1u2
1e2)''(2u2) is output, and in the same manner, the deflection correction for the second reflective surface of the second rotation is determined by the deflection correction amount (2u2).
2u2). If we pay attention to the second reflective surface, the deflection correction i(t
ug) is (ouz 0e2), the deflection correction 1f (ouz) for the second rotation is (1u21e2), and the
J gong mirror ((2u2) + (zuz
-2J), (4u2)-(3u25et). The ideal deflection correction amount for the second reflective surface is (
T12), then the amount ((ouz-0e2) rJ2)
A value proportional to is detected as (1e2), and the quantity C(xu
The value proportional to z-tea)-U,) is measured as (2e2). If expressed as this ratio coefficient k, (1e2)=k((ot12oeg)−
TW)・=・=・= (1)(zez)=k((tu
2-1e2) -HzE --...(21) Here, let the absolute value of the ratio (26z)/(tez) be α1.If the value of k is appropriately reduced, α! will become 1. Generally speaking, the absolute value of (n+182)/(He2) is αn
Since αr1 can be set to 1, by increasing the number of rotations n (Inf can be brought as close to zero as possible. Therefore, the polygon mirror +1). In this case, the deviation of the light beam becomes almost zero. It should be noted that although the above equation has been explained with focus on the second reflecting surface, it goes without saying that it is also applicable to other reflecting surfaces. Using the circuit system of the signal processing unit in Fig. 4 as a sample value control system and focusing only on one reflective surface of the polygon mirror, z = eTB (where T is the rotation period of the polygon mirror, S is a variable during Laplace transform, (e is a natural number), the function G(Z) reaching the pulse converted to Z becomes zt. Here a and b are constants. In the present invention, the timing of detecting the amount of deviation and the optical deflector (5)
11. The time difference between rf and h operation time is 11. Therefore, this should be strictly described in terms of extended Z transformation, but we will simplify the explanation by assuming that these operations occur simultaneously when the reflecting surface of the M-th polygon mirror contributes to scanning. Therefore, it is described using a simple Z transformation. In addition, in this implementation ρl, the transfer function (formula 51) is used, but it is also possible to use a transfer function expressed by a general polynomial.6 In this case, the values of the general formulas p and q are p In addition to setting = 2 and q = 1, for example, both shifts) l/register 4 [ ] 6) (121) Y can be further connected in series with 8 stages each, p:=? ), q=2, and various other options can be considered. Furthermore, in the wooden embodiment, since the polygon mirror +II has 8 stages, the number of shift stages of the shift registers (106) and (121) is also set to 8 stages, but this may be the same number or The number of shift stages may be set to be twice the number of hooks, and therefore, it is clear that the number of shift stages in this embodiment has no meaning in limiting the present invention. The present invention is suitable for use in a laser beam printer, for example, but the example shown in FIG. 1 uses a drawing laser beam to detect the deviation iQY, so the laser beam continues to be fired continuously during this detection. 1. However, depending on the wavelength used, there may be some inconveniences such as difficulty in obtaining a high-performance photoelectric detector (7J). FIG. 8 is a layout diagram of an optical system showing an embodiment in this case. In FIG. 8, the same reference numerals as in FIG.
(71) is the photoelectric detector in Fig. 1 (a photoelectric detector for detecting the amount of deviation provided in place of the force), and (12) is the irradiator that irradiates the measurement beam for detecting the amount of deviation. 71)
is a reflective surface (8) that contributes to the scanning of the polygon mirror (11).
) is arranged facing the reflective surface (8) in a fixed positional relationship with respect to the rotation axis of the polygon mirror (1), and this detector (71) includes a scanning laser beam (4 ) A focused measuring light beam (21) of any wavelength from an illuminator (12) as a separate light source is transmitted to a scanning laser beam (4) via a dichroic mirror (20) &
) is guided by the same optical system. The light-receiving surface of this detector (71) is of the four-division type in the previous embodiment. Also, the signal processing system in this case can be the one shown in FIG. 4 described above, and its detailed description will be omitted since it would be redundant. FIG. 9 ta+ shows a modification of the photoelectric detector, and here, instead of the four-part photoelectric detector (force or (71)), three photoelectric elements (72A), (72B), and (72G) are used. )
A three-part photoelectric detector (72) Y is used. That is, the scanning trajectory (61)Y of (60) in FIG. 9 (spora of the focused laser beam on the scanning plane in al)
Photoelectric elements (72A) and (72C) are arranged facing each other vertically in between, and another photoelectric element (72
B) is arranged so as to cross the scanning trajectory (61)Y. The photoelectric element (72B) that is irradiated by the spot (60) before other photoelectric elements is a timing photoelectric element, and its width in the running direction is preferably the spot.
It is preferable to make it approximately equal to the diameter of (60). The pair of upper and lower photoelectric elements (72A) (72C) are photoelectric elements for detecting misalignment, and their function is similar to that of the 4-segment photoelectric detection 2 of the above-mentioned example.
Photoelectric element (7A) (7(,
') is similar. When using this modified photoelectric detector (72), in the circuit shown in FIG.
111), differential circuit (112), comparator (113)
), in place of the AND circuit (114), a comparator (125) is connected to the input terminal (HUB) as shown in i9 factor (bl).
and its output directly to a monostable multivibrator (
115) as a trigger signal. Figure 9 (
In bl, (126) is the comparison ``acid injection power vl'' of the comparator (125), and the input terminal (101A) receives the ``c output signal'' of the photoelectric element (72A).
101C) is the received light output signal of the photoelectric element (72C).
And the input Dil'a element (101B) has a photoelectric element (7
2B) are respectively inputted. Now, assuming that the width dimension of the light beam (72B) in the scanning direction is approximately equal to the diameter of the spora (60), the photoelectric element (72B) is ), an output signal that changes over time as shown in waveform (1) in Figure 10 is obtained, and the
As a result, from the differential circuit (102) that calculates the difference between the output signals of the photoelectric elements (72A) and (72C), an output signal that changes over time as shown in the waveforms (A-C) in Fig. 10 is obtained. Here, the photoelectric element (7) is detected by the comparator (125).
By slicing the output signal fBl'a=ratio 11R level Vr of 2B), its peak 8. A trigger pulse is output from the comparator (125) at lI point tp, and this trigger pulse triggers the monostable multivibrator (115). The monostable multivibrator (115) gives a pulse to the sample and hold circuit (103) at a preset time tsi after being triggered and outputs the output signal LA-C of the differential circuit (102).
is taken into the sample hold circuit (1[13) and held. In this way, even in the modified example of FIG. The width dimension in the scanning direction of the spot (60) was set to be approximately equal to the diameter of the spot (60); however, in order to measure the beam power, the above width dimension may be made larger than the diameter of the spot (60). In this case, the timing of detecting the amount of deviation is based on the rising or falling point of the output signal of the photoelectric element (72B), and after a period of time from that point, the differential circuit (102B) is detected.
) may be used to send an output signal representing the amount of deviation from the current value. Regarding the determination of the timing of detecting the amount of deviation, many variations are possible in addition to the above example. It is also possible to determine the timing by using the difference between the outputs of the photoelectric elements (7B) and (7D).
) (7D) output difference (13-D) is shown in Figure 5, but this difference signal CB-D) w is passed through the circuit shown in No. 111 and then output to the monostable multivibrator in Figure 4. (1
15) Try to trigger a keto trigger. In Figure 11, the difference signal (B-D) is transmitted through two comparators (127) (1
28), and one comparator (127) compares the positive and negative threshold levels (V+II) (V
Koto Ic J: Difference signal (B-D) level (V+H
) and then drops to the level (V-H) to obtain a signal Sl that becomes logic "1", and in the other comparator (12B), the difference signal (13-1)) becomes the level (V-H). Signals 82 and 82 are logic bits for a period of more than 10H), and these two signals Sl and 82 are connected to an exclusive OR circuit (
129), and the difference signal (
A trigger signal 83 is obtained with a pulse width only while the level (B-D) falls to the level (v+10 colors (■-H)), and this trigger signal S3 triggers the monostable multipipe lake (t15) of the circuit shown in Figure 4. as if a
6. As described above, according to the present invention, a trigger (timing) signal as scanning position information of a light beam spot can be obtained, and a reflective surface that contributes to scanning can be obtained while the polygon mirror serving as the main scanning means is rotating. The amount of scanning deviation due to the inclination angle of is automatically detected as the deviation amount for each reflecting surface, and based on this deviation amount, deflection correction is performed corresponding to each reflecting surface that contributes to scanning while the polygon mirror is rotating. Therefore, there is no need to adjust the scanning deviation as a device, and there is no need to make the deflection operation amount of the deflection means for deflection correction completely correspond to the deflection correction amount as a deflection command value. Even if an inexpensive element with a hysteresis characteristic is used as a drive element for a deflection means, a highly accurate deflection correction operation can be achieved due to the correction value based on the actual value of the correction amount. There is no need to strictly control the accuracy of the angle of inclination of each reflective surface, and the manufacturing of the polygon mirror itself becomes easier, providing numerous advantages in terms of production and use of the optical beam scanning device. be. Furthermore, the embodiment of the present invention described above has the advantage that even in a scanning device where the optical beam power changes, it is possible to perform scanning f and Y detection without depending on the beam power, and at the same time, it is possible to monitor the beam power. ing. Further, in order to detect the timing of irradiating the photoelectric element for detecting the deviation of a pair of spotters, a photoelectric element for timing is provided (π), so that the amount of deviation of the spot from the scanning trajectory can be accurately detected. For example, when a spot is located at the center of the light receiving part of a photoelectric element for detecting deviation, the output signal of that element can be sampled, so there is no need to sample the rising or falling parts of the output signal, and the long-term This has the effect of greatly improving stability and accuracy.

[Brief explanation of drawings]

Fig. 1 is a layout diagram schematically showing the main configuration of the first embodiment of the present invention, Fig. 2 is a layout diagram showing the previous optical system during scanning, and Fig. 6 is a schematic diagram showing an example of a photoelectric detector. 4 is a block diagram showing a configuration example of a signal processing unit as a main part of the present invention, FIG. 5 is a waveform diagram for explaining the operation of a photoelectric detector, and FIG. 6 is a photoelectric detector as well. Figure 7 is a diagram showing the relationship between the detection output of the detector and the deviation angle of the scanning beam due to the inclination of the reflective surface of the polygon mirror.
The figure is a layout diagram schematically showing the main configuration of the second embodiment of the present invention, FIG. 9(a) is a front view schematically showing a modified example of the photoelectric detector, and FIG. Main part block diagram showing the changed part of the circuit in Fig. 4 when using a photoelectric detector, Part 1
Fig. 0 is a waveform diagram for explaining the output signal processing of the photoelectric detector according to Fig. 9 (tag (b)), and Fig. 11 is a circuit block showing a trigger signal generation part used in yet another modification of sampling timing determination. 12 are waveform diagrams for explaining the operation of the modified relay shown in the previous figure. (1) Single rotation polygon mirror + +2) : Focusing lens, (6) : Scanning surface, (4) - Incident laser beam, (5
) - Optical deflector - (61: Focused laser beam, (6o>
: Beam spot, (73, (71): Photoelectric detector, (
7A) (713) (7C)t7D): Photoelectric element, (8)
: Reflective surface, (9): Piezo drive unit, (10): Signal processing unit, (11C measurement light beam, (12): Irradiator,
(102): Differential circuit, (103): Sample and hold circuit, (104): Divider, (+05): A
/IE converter, (106): first shift register, (
108) (115) : Monostable multivibrator, (
119) (120): Latch circuit, (12i): Second
Shift register, (122): Subtractor. Agent Patent attorney San Akira Kimura,, 3 Figures 4 Figures 1 (Figure 5 Figure 6 Off) m-”shi-ichiichi

Claims (1)

[Scope of Claims] (1) Scanning means for moving the light beam in one predetermined direction in order to linearly scan a scanning surface with the spot of the light beam; a pair of photoelectric elements for detecting deviation, which are irradiated with the light beam and become substantially equal to each other when in orbit, and output different photoelectric signals in accordance with the deviation when the spot deviates from the scanning orbit; and; when scanning with the spot of the light beam, the light beam is arranged to be irradiated by the original beam temporally earlier than the photoelectric element for displacement detection, and the light beam irradiates the photoelectric element for displacement detection. a timing photoelectric element for determining timing; and detecting a deviation of the light beam spot from the predetermined scanning trajectory from both photoelectric wires of the pair of deviation detection photoelectric elements in response to an output signal of the timing photoelectric element; and a correction means for optically correcting the deflection of the light beam based on the amount of shift so as to eliminate uneven scanning of the light beam spot by the scanning means. A light beam scanning device. (2) Two timing photoelectric elements are arranged one after the other on the predetermined scanning trajectory, and each of the four photoelectric elements, these two timing photoelectric elements and the pair of deviation detection photoelectric elements, is arranged one after the other on the predetermined scanning trajectory. , the light beam scanning device according to item 1 of the patent application, characterized in that one light beam scanning device is arranged in each of four quadrants of orthogonal coordinates on the scanning plane, the origin of which is located on the predetermined scanning trajectory. (6) The deviation detecting means comprises the pair of gaps 11. a first subtraction means for obtaining a difference value between the two photoelectric signals of the two photoelectric elements for detection; a second subtraction means for obtaining a difference value between the two photoelectric signals of the two photoelectric elements for timing; When the difference value obtained by the second subtraction means becomes substantially zero with a predetermined dead zone width 7 while the beam is being irradiated, the difference value obtained by the first subtraction means is extracted as the deviation amount. 3. The light beam scanning device according to claim 2, further comprising: sampling means for;