JP2694265B2 - Scan position detecting device in optical scanning system - Google Patents

Description

The present invention relates to, for example, a device for detecting the position of a minute scratch or an adhered substance on the surface of an object, a device for detecting the size of a minute object, or a laser type device. Scanning spots (positions) of the scanned light beam in an optical scanning system that forms the main part of various devices such as printers and PPCs.
More specifically, the present invention relates to a scanning position detecting device for detecting a beam, and more specifically, a demultiplexer for obtaining a single branched scanning light beam from a main scanning light beam scanned by a light deflector to a target range including an irradiation target. And a transmission type grating having a large number of periodic slits is arranged in the scanning range of the one branch scanning light beam, and the one branch scanning is transmitted through the slit group of the transmission type grating. Scanning in an optical scanning system provided with a photodetector for detecting a light beam as a pulse train, and detecting the scanning position of the main scanning light beam based on the detection result of the pulse train output from the photodetector. The present invention relates to a position detection device (hereinafter, simply referred to as a scanning position detection device). [Prior Art] The scanning position detecting device has conventionally been configured as shown in FIG. That is, in this figure, 01 is the main scanning light beam 0A to the target range including the irradiation object (not shown).
Reference numeral 02 denotes a light deflector that reciprocally scans, and 02 is a demultiplexer for obtaining the branched scanning light beam 0B from the main scanning light beam 0A. Reference numeral 03 denotes a transmissive grating arranged in the scanning range of the branched scanning light beam 0B. In this transmissive grating 03, a plurality of slits 0s having a constant width are arranged at constant intervals (equal intervals). The slit group 03s is formed. And 0
4 is a photodetector that detects the branched scanning light beam 0B that has changed in intensity by passing through the slit group 03s in the transmission type grating 03 as a pulse train, and 05 is a signal processing unit for the pulse train output from the photodetector 04. In order to detect the scanning position of the main scanning light beam 0A in real time by counting the number of pulses in the pulse train, an amplifier, a waveform shaping circuit, a pulse counter, etc. are included. [Problems to be Solved by the Invention] In the above conventional scanning position detecting device, the branched scanning light beam 0B is converted into a pulse train, and the scanning position of the main scanning light beam 0A is counted by counting the number of pulses of this pulse train. Since a digital measuring method is used to detect, the scanning time from the reference time point triggered by the timing light receiving element is detected, and the scanning angle is detected by the angle sensor attached to the optical deflector 01. Compared with the one that adopts a traditional analog-type measurement method such as detecting, the influence of the non-linearity of the optical deflector 01 or the motor for driving it or the non-linearity of the angle sensor is directly However, it still has the following problems. That is, the resolution of the scanning position detecting device based on the pulse counting method is the same as that of the transmission type grating used for it.
It is determined by the width of each slit 0s in 03, but the width of the slit 0s cannot be narrower than a certain value in relation to the spot width of the branch scanning light beam 0B, and the spot of the branch scanning light beam 0B Since there is naturally a limit to the width reduction, in the conventional scanning position detecting device using the single transmission type grating 03, its resolution is determined by the minimum slit width regulated by the spot width of the branched scanning light beam 0B. It was impossible to raise the resolution beyond the limit. Further, as in this conventional example, in order to eliminate interruption and waste of scanning time, it is common to reciprocally scan the light beam 0A (0B) by using the reciprocating rotary type optical deflector 01. In such a case, in the above-mentioned conventional scanning position detecting device, the output pulse train from the single photodetector 04 used for the conventional scanning position detecting device is irrespective of the scanning direction (forward and backward) of the light beam 0A (0B). Since the shape is always constant, the light beam 0A (0B) is emitted from the detection pulse train itself.
The scanning direction of the optical beam 0A (0B) cannot be determined. Therefore, in order to detect the scanning direction of the light beam 0A (0B), for example, a special sensor such as a sensor for detecting the rotation direction of the optical deflector 01 must be provided. did not become. The present invention has been made in consideration of the above matters,
The purpose is to be able to exhibit a resolution significantly higher than the limit resolution determined by the minimum slit width regulated by the spot width of the scanning light beam, and also to easily determine the scanning direction of the scanning light beam from the detection pulse train itself. It is to provide a scanning position detecting device capable of performing the same. [Means for Solving the Problems] In order to achieve the above object, according to the present invention, one branched scanning light beam is obtained from a main scanning light beam scanned by a light deflector to a target range including an irradiation target. And a transmission type grating having a slit group in which a large number of slits having a constant width are arranged at a constant interval, is arranged in the scanning range of the one branched scanning light beam, and the slit group is A photodetector that detects the transmitted one branch scanning light beam as a pulse train is provided, and the scanning position of the main scanning light beam is detected based on the detection result of the pulse train output from the photodetector. In the scanning position detecting device in the optical scanning system, the transmission type grating has a first slit group in which a plurality of slits having a constant width are arranged at a constant interval. A first grating portion and a second grating portion having a second slit group in which a large number of slits having the same width as the slits of the first slit group are arranged at the same intervals as in the first slit group, and Both of these grating portions are vertically separated from each other in a state of being shifted in the width direction so that the slits forming the first slit group and the slits forming the second slit group do not overlap each other.
It is arranged in parallel in a step, and further, is irradiated with one branch scanning light beam that has passed through the demultiplexer, and is configured to obtain a single spot on the irradiation surface in the juxtaposed direction, The photodetector detects a branched scanning light beam that has passed through the first slit group as a first pulse train, and a branched scanning light beam that has passed through the second slit group as a second pulse train. Signal processing for detecting the scanning position of the main scanning light beam based on a pulse train obtained by combining the first pulse train and the second pulse train output from each of the photodetectors. And a light shielding plate for preventing crosstalk between the first grating portion and the first detector and the second grating portion and the second detector. [Operation] According to the scanning position detecting device of the present invention having the above-mentioned characteristic configuration, the detection resolution of the scanning position of the branched scanning light beam, and further of the main scanning light beam, is the minimum regulated by the spot width of the branched scanning light beam A resolution significantly higher than the limit resolution determined by the slit width (at least twice as much as that in the conventional case) is exhibited, and even when the split scanning light beam is reciprocally scanned, the first photodetector and the second light are detected. Since a signal whose level is inverted when the scanning direction is inverted appears from the logical signal obtained by combining the first pulse train and the second pulse train output from the detector, respectively, the scanning directions of the main scanning light beam and the branch scanning light beam are changed. Can be easily determined from the detection pulse train itself. [Embodiment] Hereinafter, a specific example of the scanning position detecting device of the present invention will be described.
This will be described with reference to FIGS. 1 to 4 show a first embodiment of the present invention. As shown in FIG. 1, an optical deflector 1 which is composed of, for example, a reciprocating rotary mirror and which is generally called an optical scanner is used to reach a target range including an object to be measured or an irradiation object such as a PPC photosensitive drum. In an optical scanning system configured to reciprocally scan a main scanning light beam A such as a Ne gas laser, in order to obtain one branched scanning light beam B from the main scanning light beam A, a demultiplexer including, for example, a half mirror 2 is provided on the optical path of the main scanning light beam A. Reference numeral 3 denotes a transmission type grating (diffraction grating) provided at a position where one branching scanning light beam B from the demultiplexer 2 can be irradiated, and is configured as follows. That is, for example, as shown in an enlarged view in FIG. 2, the transmission type grating 3 has two grating portions 3I and 3II which are arranged in upper and lower portions.
It is arranged in parallel on the stage. Each of the grating portions 3I and 3II includes a first slit group 3Is and a second slit group 3IIs in which a large number of slits s having the same width a are arranged at a constant interval b. In this embodiment, the width a of the slit s and the width (b-a) of the shielding portion between two adjacent slits s are set equal to each other, that is, a = 1 / 2b,
Moreover, the first grating portion 3I in the upper stage and the second grating portion 3II in the lower stage are arranged such that the slits s in them are displaced from each other by half the width a in the width direction, and one slit is passed through the duplexer 2. The branched scanning light beam B is irradiated together, and a single circular spot SP having a radius equal to the width a of the slit s is obtained over the irradiation surface in the juxtaposed direction. The grating portions 3I and 3II constituting the transmissive grating 3 are formed by, for example, depositing a substance such as a metal that does not transmit light at a predetermined interval on the surface of a glass plate, and a portion where no light non-transmitting substance is deposited becomes a slit s It is manufactured by using the portion on which the light non-transmissive material is deposited as a shielding portion. In that case, the grating portions 3I and 3II may be integrally manufactured so that the slits s thereof are displaced from each other, but they may be separately manufactured and then combined so that the slits s are displaced from each other. 4I and 4II are a first photodetector and a second photodetector, and the first photodetector 4I uses the branched scanning light beam that has passed through the first slit group 3I s of the first grating portion 3I as a first pulse train. The second photodetector 4II is configured to detect the branched scanning light beam that has passed through the second slit group 3IIs of the second grating portion 3II as a second pulse train. A signal processing unit 5 detects the scanning position of the main scanning light beam A on the basis of a pulse train obtained by combining the first pulse train and the second pulse train output from the photodetectors 4I and 4II, respectively. Is configured. The detailed configuration is as shown in FIG. 6 is the first grating portion 3I and the first detector 4I
And a light shield plate for preventing crosstalk, which is interposed between the second grating portion 3II and the second detector 4II.
That is, the light shield plate 6 has the first grating portion 3I.
Of the branched scanning light beam B transmitted through the first slit group 3I s of
And the second slit group 3II s of the second grating portion 3II
It is provided in order to reliably prevent crosstalk with the branched scanning light beam B that has passed through. FIG. 3 is a block circuit configuration diagram showing details of the signal processing unit 5, and FIG. 4 is a chart showing waveforms and timings of signals in the respective units. That is, the first pulse train output from the first photodetector 4I passes through the first amplifier 7I and is then waveform-shaped by the comparator 8I to become a signal as shown in FIG. 4, which is the first exclusive OR described later. It is supplied to the circuit 9 and the inverter 11. On the other hand, the second pulse train output from the second photodetector 4II passes through the second amplifier 7II and is then waveform-shaped by the comparator 8II to become a signal as shown in FIG. 4, and the first exclusive OR circuit 9 And the second described below
It is supplied to the exclusive OR circuit 14. In this case, the phase of the signal obtained by waveform-shaping the first pulse train is 90 degrees (1/4 cycle) ahead of the phase of the signal obtained by waveform-shaping the second pulse train,
On the contrary, it is 90 degrees (1/4 cycle) behind in the backward scan. Therefore, the output signal from the first exclusive OR circuit 9, that is, the combined signal as an exclusive OR of the signals, as a whole (that is, a special waveform generated at the time of inversion between the forward scanning and the backward scanning). Except for the above), a pulse train having a half cycle of both of these signals, respectively. Then, the output signal is input to the monostable multivibrator 10 and one shot is triggered at the rising and falling edges thereof, and as a result, the output signal from the monostable multivibrator 10 waveform-shaped the first pulse train. The pulse train has a period of 1/4 of that of the signal and the signal obtained by waveform-shaping the second pulse train. This signal is input as a clock signal to the up / down counter 15 and the latch circuit 13 described later. On the other hand, the signal obtained by waveform-shaping the first pulse train input to the inverter 11 is inverted there, and then delayed by a 1/4 cycle by the delay circuit 12 and then input to the latch circuit 13, where the monostable multivibrator is provided. Latch circuit 13 is latched by the rising edge of the clock signal from 13
The output signal of has a waveform as shown in FIG. The output signal from the latch circuit 13 and the second
The signal obtained by shaping the waveform of the pulse train is input to the second exclusive OR circuit 14, and a signal as an exclusive OR of the signals is obtained. The signal output from the second exclusive OR circuit 14 is an up / down counter that is an up / down signal that is inverted from an up-count signal to a down-count signal when inverted from the forward scan to the backward scan.
Input to 15. Therefore, the up / down counter 15 receives the branch scanning light beam B from the counting result based on the output clock signal from the monostable multivibrator 11 and the output up / down signal from the second exclusive OR circuit 14, which are input to the up / down counter 15. As a result, the scanning position coordinates of the main scanning light beam A are detected and output. The detection resolution of the scanning position coordinates at that time is 1/4 of the respective cycles of the signal obtained by waveform-shaping the first pulse train and the signal obtained by waveform-shaping the second pulse train of the clock signal. Therefore, a resolution four times as high as the resolution corresponding to the array period of the slits s in each of the slit groups 3I s and 3II s formed in 3 can be obtained. This corresponds to at least twice the resolution of the conventional case. By the way, in the above-described first embodiment, the branch scanning light beam B having a circular cross section is used, and the transmission type grating 3 having an integral plane structure is provided in a direction orthogonal to the optical axis of the branch scanning light beam B. Although the spot SP formed over the first grating portion 3I and the second grating portion 3II has a circular shape, the spot SP is replaced by the spot.
The shape of the SP may be a long elliptical shape as shown in FIG. In such a case, there is an advantage that the S / N is improved, and the transmission grating 3
In the above, the allowable range of the degree of coincidence between the boundary center line of the first grating portion 3I and the second grating portion 3II and the scanning center line of the branched scanning light beam B becomes loose, and the slit groups 3I s, 3II s There is an advantage that a miscount due to a defect is unlikely to occur. As means for making the shape of the spot SP into a long elliptical shape, the first grating portion 3I and the second grating portion 3II are provided by inclining with respect to the optical axis of the branched scanning light beam B having a circular cross section, or Alternatively, the transmission type grating 3 may be provided perpendicularly to the optical axis of the branched scanning light beam B, and a cylindrical lens may be placed behind the demultiplexer 2. The present invention is not limited to the above-mentioned embodiment, but can be carried out by being modified in various ways, and the first grating portions 3I, 3II constituting the transmission type grating 3 can be implemented.
The upper and lower sides of the slits s constituting the first slit group 3I s and the slits s constituting the second slit group 3IIs are shifted in the width direction so as not to overlap with each other.
It is sufficient if they are arranged side by side. Then, the first slit group 3I s and the second slit group 3I
The width of each slit s in I s and the width of the shielding portion between two adjacent slits s may not necessarily be equal. Further, the spot SP straddles each of the slits s in the upper and lower two-stage slit groups I and II, and in the case of a circle, the orthogonality does not exceed the interval b of the slits s, and in the case of an elliptical shape, the spot SP is short. The diameter may be set to a size that does not exceed the interval b of the slits s. [Advantages of the Invention] The scanning position detecting device of the invention is configured as described above, and has the following effects. That is, as the detection resolution of the scanning position of the branched scanning light beam, and further of the main scanning light beam, a high resolution of 4 times the resolution corresponding to the arrangement interval of the slits in each slit group in the transmission type grating is obtained.
A remarkably higher resolution than the limit resolution determined by the minimum slit width regulated by the spot width of the branched scanning light beam can be obtained. When the branched scanning light beam is reciprocally scanned, the level is inverted at the time of reversing the scanning direction from the logic signal obtained by combining the first pulse train and the second pulse train output from the first photodetector and the second photodetector, respectively. Since the signal appears, the scanning directions of the main scanning light beam and the branched scanning light beam can be easily determined from the detection pulse train itself. Therefore, as is conventionally the case, special means such as a scanning direction detecting sensor is used. In addition to eliminating the need to provide it, accurate position detection can be performed even if the scanning direction, the scanning amount, and the scanning speed of the branched scanning light beam are arbitrarily changed within the scanning range. That is, unlike the scanning position detecting device of the present invention, it does not straddle the first grating portion and the second grating portion in the juxtaposed direction.
As described in JP-A-55-57826, compared to the case where there are as many branched lights as there are grating portions and a single spot is formed by the number of each grating portion (hereinafter referred to as a comparative example). , At least having the following advantages: A. In the comparative example in which the branched light is present by the number of the grating portions, only the case where the number of the branched lights is 2 will be described.
A single spot formed on the grating portion and formed by the other branched light is formed on the second grating portion. In this case, if there is no deviation in both spots and they are arranged in each grating portion, Like the single spot in the invention, there is no problem because a 90 ° phase difference occurs, but in the comparative example, two branched light beams are formed by using an optical system branching means such as a beam splitter or a diffraction grating. Therefore, the arrangement of both spots may be deviated due to the influence of the optical system branching means. Therefore, when a shift occurs in the comparative example, the phase difference disappears, and eventually it becomes difficult to detect the scanning direction, and the single spot in the present invention is two single spots by the two split lights. Compared to using
There is no spot deviation and there is always a 90 ° phase difference, which is clearly advantageous in that the scanning direction can be determined. B. More specifically, in the comparative example, the method of making the branched light incident on the detector is different. Of the two signal tubes may change due to the change in the positional relationship of the two signal tubes.
Since it is determined whether the signal phase is advanced or delayed, if the phase difference disappears due to the optical system branching unit even though it advances in a certain direction, it becomes impossible to determine the scanning direction, An error will also occur. On the other hand, according to the present invention, as described above, the spot on the transmission type grating can be set to a circular single spot or an elliptical single spot long in the juxtaposing direction of two grating portions. It has the advantage of being able to prevent buffering between the two signals of the first photodetector and the second photodetector, and a spot of a single light beam that has passed through the same optical system is incident on both photodetectors. Therefore, the phase difference between the two signals is less likely to change than in the comparative example, and therefore, there is no possibility of causing an error in position detection.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 show an embodiment of the present invention, FIG. 1 is a diagram schematically showing the overall configuration of a scanning position detecting device of the present invention, and FIG. FIG. 3 is a partially enlarged front view of a transmission type grating which is a main part of the scanning position detecting device, FIG. 3 is a circuit configuration diagram showing a configuration of a signal processing unit of the scanning position detecting device, and FIG. 4 is a signal in each part of the signal processing unit. 2 is a chart showing waveforms and timings of FIG. FIG. 5 is a partially enlarged front view of a transmission type grating in another embodiment of the present invention. FIG. 6 is a diagram schematically showing the overall configuration of a conventional scanning position detecting device. 1 ... Optical deflector, 2 ... Demultiplexer, 3 ... Transmission type grating, 3I ... 1st grating part, 3Is ... 1st
Slit group, 3II ... 2nd grating part, 3II s ...
… Second slit group, 4I …… First photodetector, 4II …… Second
Photodetector, 5 ... Signal processing unit, 6 ... Shading plate, A ... Main scanning light beam, B ... Branching scanning light beam, s ... Slit.

Claims (1)

(57) [Claims] A slit is provided with a demultiplexer for obtaining a single branched scanning light beam from a main scanning light beam scanned by a light deflector to a target range including an irradiation target, and a plurality of slits having a constant width arranged at a constant interval. A transmission type grating having a group is arranged in a scanning range of the one branch scanning light beam, and a photodetector for detecting the one branch scanning light beam transmitted through the slit group as a pulse train, In the scanning position detecting device in the optical scanning system configured to detect the scanning position of the main scanning light beam based on the detection result of the pulse train output from the photodetector, the transmission type grating has a constant width. First grating portion having a first slit group in which a large number of slits are arranged at regular intervals, and a width equal to the width of the slit of the first slit group. Second slit portion having a second slit group in which a large number of slits are arranged at the same intervals as those in the first slit group, and both of these grating portions are a slit and a second slit constituting the first slit group. The slits forming the group are arranged side by side in two rows in a state of being shifted in the width direction so as not to overlap with each other, and further, one branch scanning light beam that has passed through the demultiplexer is irradiated together. , A single spot is formed on the irradiation surface in the juxtaposed direction, and the photodetector detects the branched scanning light beam transmitted through the first slit group as a first pulse train. It comprises a first photodetector and a second photodetector that detects the branched scanning light beam that has passed through the second slit group as a second pulse train. And a signal processing unit for detecting a scanning position of the main scanning light beam based on a pulse train obtained by synthesizing the first pulse train and the second pulse train that are output, and further, the first grating portion and the first detection unit. Position detecting device in an optical scanning system, wherein a light-shielding plate for preventing crosstalk is interposed between the detector and the second grating portion and the second detector. 2. The scanning position detecting device in the optical scanning system according to claim 1, wherein the transmission type grating is arranged so as to be orthogonal to the optical axis of one branch scanning beam. 3. The scanning position detecting device in an optical scanning system according to claim 1, wherein the transmission type gratings are arranged so as to be inclined with respect to the optical axis of one branch scanning beam and intersect with each other. 4. A slit is provided with a demultiplexer for obtaining a single branched scanning light beam from a main scanning light beam scanned by a light deflector to a target range including an irradiation target, and a plurality of slits having a constant width arranged at a constant interval. A transmission type grating having a group is arranged in a scanning range of the one branch scanning light beam, and a photodetector for detecting the one branch scanning light beam transmitted through the slit group as a pulse train is provided; In the scanning position detecting device in the optical scanning system configured to detect the scanning position of the main scanning light beam based on the detection result of the pulse train output from the photodetector, the transmission type grating has a constant width. First grating portion having a first slit group in which a large number of slits are arranged at regular intervals, and a width equal to the width of the slit of the first slit group. Second slit portion having a second slit group in which a large number of slits are arranged at the same intervals as those in the first slit group, and both of these grating portions are a slit and a second slit constituting the first slit group. The slits forming the group are arranged side by side in two rows in a state of being shifted in the width direction so as not to overlap with each other, and one branch scanning light beam that has passed through the demultiplexer is irradiated together. , A single spot is formed on the irradiation surface in the juxtaposed direction, and the photodetector detects the branched scanning light beam transmitted through the first slit group as a first pulse train. It comprises a first photodetector and a second photodetector that detects the branched scanning light beam that has passed through the second slit group as a second pulse train. And a signal processing unit for detecting a scanning position of the main scanning light beam based on a pulse train obtained by synthesizing the first pulse train and the second pulse train that are output, and further, the first grating portion and the first detection unit. A light-shielding plate for preventing crosstalk between the detector and the second grating portion and the second detector, and the transmission type grating is orthogonal to the optical axis of one branch scanning beam. And a cylindrical lens disposed between the transmission grating and the rear stage of the demultiplexer, the scanning position detecting device in the optical scanning system.