JPH01259316A - Light beam scanner - Google Patents

Abstract

PURPOSE:To easily judge abnormality of the beam diameter by counting an effective output time of an output signal of a light beam detecting means, comparing its output time with a prescribed time of a reference and outputting an error signal, when said output time is outside of the range. CONSTITUTION:A laser beam 7 is brought to photoelectric conversion by a photodiode of the tip of an optical fiber 14, and brought to current - voltage conversion by an operational amplifier 16 and a feedback resistor 17. A voltage level of this output signal is compared with a reference voltage 19 by a comparator 18, and in case the output signal is higher than the reference voltage 19, a BD signal is outputted. Subsequently, in a timer circuit and a latch circuit 23, a turn-on time (effective output time) of said BD signal is counted, compared with an output time of a reference in case of a normal beam diameter, and when it is outside of the range, an error signal ERR is outputted. Therefore, abnormality of the beam diameter is judged easily and deterioration of an image can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device having a light beam monitoring function, and particularly to a light beam scanning device used in a laser beam printer or the like.
The present invention relates to a light beam scanning apparatus having a light beam scanning means for forming an image by scanning a light beam and irradiating the photoreceptor with the light beam.

[Prior Art] Conventionally, in a laser beam printer or the like, a light beam scanning device of this type that horizontally scans a light beam is generally known to have a configuration as shown in FIG.

In FIG. 5, 2 is a laser unit that modulates the laser beam on and off based on the image signal (VDO signal) 1. 4 is a motor that rotates the rotating polygon mirror 5 at a constant speed. Reference numeral 5 denotes a rotating polygon mirror that deflects the laser beam 3 modulated on and off by the laser unit 2.

Reference numeral 6 denotes an imaging lens that forms an image of the laser beam 7 deflected by the rotating polygon mirror 5 onto the photosensitive drum 8 . A beam detector 9 detects the laser beam deflected by the rotating polygon mirror 5. The beam detector 9 is arranged on the optical path between the light reception start position A of the rotating drum and the rotating polygon mirror 5. When the beam detector 9 detects the 1 nose beam, it detects the beam position detection No. 43 (BD double signal 11). Output.

As the beam detector 9, a photoelectric conversion element such as a photodiode can be used. Reference numeral 12 denotes a transfer paper serving as a recording medium on which the latent image formed on the photosensitive drum 8 is transferred via developer (toner) of a developing device (not shown).

Next, the operation of the conventional example will be explained.

Laser unit 2 emits laser beam 3 according to image signal 1
occurs. The laser beam 3 modulated in an on-off manner is deflected by a rotating polygon mirror 5 and focused on a rotating drum 8 via an imaging lens 6 . Since the rotary polygon mirror 5 is rotated at a constant speed by the motor 4, the imaging position of the deflected laser beam 7 moves in the direction of arrow AA on the photosensitive drum 8 (horizontal scanning).

A latent image is formed on the photosensitive tram 8 as a recording medium by exposure to the laser beam 7. Further, the photosensitive tram 8 rotates in the direction of arrow BB force, and the latent image formed on the photosensitive drum 8 is developed by a developing device (not shown), and the developed image is transferred onto the transfer paper 12.

Prior to horizontal scanning of the laser beam 7, the beam detector 9
When B detects the laser beam 7, the beam detector 9 detects the laser beam 7.
A D signal 11 is output. Based on this BD (i number 11), a control unit (not shown) controls the timing of transferring the VDO number 1 to the laser unit 2. Therefore, the VDO signal for one scan is synchronized with the BD signal 11. 1 is transferred to the laser unit 2, and the transfer paper 12 is transferred to the laser unit 2 by a double operation sequence.
The image is played above. Furthermore, the exposure start position on the photosensitive drum 8 in the main scanning direction AA is also defined by the BD signal 11 .

FIG. 6 shows the timing of generation of the above-mentioned BD signal 11 and VDO signal 1. In FIG. 6, at timing E, first, a VDO signal 1 for detecting the exposure start position is sent to the laser unit 2. A laser beam generated by this vDo signal is detected by a beam detector 9, and at timing F, a BD signal 11 is generated.

[When the ID signal 11 is transferred to the control unit (not shown), after a time T from timing F, the vDo signal 1 is transferred for a time a]
A control unit (not shown) transfers the information to the laser unit 2.
takes control. Thereafter, the pulse E for detecting the exposure start position is transferred to the laser unit 2 as a horizontal synchronization signal every time T2.

[Problems to be Solved by the Invention] However, the conventional device as described above does not have any means for detecting the beam diameter of a horizontally scanned light beam such as a laser beam.
If distortion occurs in the optical system, even if an abnormality occurs in the beam diameter due to a change in the characteristics of the laser diode in the laser unit (for example, due to deterioration), image formation will continue as is, and the quality of the reproduced image or recorded image will deteriorate. However, there were problems such as a significant drop in performance.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a light beam scanning device having a light beam monitoring function capable of detecting an abnormality in the beam diameter of a light beam.

[Means for Solving the Problems] In order to achieve the above object, the first aspect of the present invention is a light beam scanning device having a light beam scanning means for forming an image by scanning a light beam and irradiating the photoreceptor with the light beam. In,
A light beam detection means for detecting the light beam, a comparison means for comparing the level of the detection signal of the light beam detection means and a reference voltage, and a timer for measuring the output time of the output signal of the comparison means and determining that the output time is within a predetermined allowable time. The present invention is characterized by comprising a clock means for outputting an error signal when the time is outside the range.

Further, in order to achieve the above object, a second aspect of the present invention is to detect a light beam in a light beam scanning device having a light beam scanning means for forming an image by scanning the light beam and irradiating the photoreceptor with the light beam. A light beam detection means, a differentiation circuit that differentiates the detection signal of the light beam detection means, and a comparison that compares the level of the output signal of the differentiation circuit and a reference voltage, and outputs an error signal if the output signal does not reach the reference voltage. It is characterized by comprising means.

[Function] According to the above-described first configuration, when the beam diameter of the horizontally scanned beam increases or decreases from a normal size, the detection signal of the light beam detection means and the reference voltage The output time of the output signal of the comparing means (
Since the time when the light beam is turned on) is outside the predetermined allowable time range that is set based on the output time for a normal beam diameter, an error signal is output from the timing means and an abnormality in the light beam diameter is detected. This makes it possible to prevent deterioration in the image quality of reproduced images and recorded images.

Further, the present invention provides the above-mentioned second configuration, so that the beam diameter of the horizontally scanned beam is expanded from the normal size,
When the light intensity decreases, the level of the output signal of the differentiating circuit that differentiates the detection signal of the light beam detection means does not reach the reference voltage determined based on the case of a normal light beam, so an error signal is output from the comparison means. Therefore, it is possible to detect an abnormality in the diameter of the light beam or a decrease in the light intensity of the light beam, and it is also possible to prevent deterioration in the quality of reproduced images and recorded images.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1(A) and 1(B) each show the basic configuration of an embodiment of the present invention.

In this figure (A), A is a light beam detection means for detecting the light beam in a light beam scanning device having a light beam scanning means for scanning a light beam and irradiating the photoreceptor to form an image. . Reference numeral B denotes comparison means for comparing the levels of the detection signal of the light beam detection means A and the reference voltage.

Reference numeral C denotes a timer that measures the output time of the output signal of the comparator B and outputs an error signal if this output time is outside a predetermined allowable time range.

Further, in this figure (B), A is a light beam detection means similar to the above. D is a differentiation circuit for differentiating the detection signal of the light beam detection means A.

E compares the level of the output signal of the differentiating circuit with the reference voltage, and the output signal is the base! ! : Comparison means that outputs an error signal if the voltage does not reach the voltage.

FIG. 2 shows a circuit configuration of a first embodiment of the present invention, and parts similar to those of the conventional example shown in FIG. 5 are given the same reference numerals.

In FIG. 2, 13 is a slit arranged on the scanning plane of the laser beam 7, that is, on the optical path between the light reception start position A of the rotating drum 8 and the rotating polygon mirror 5, and the laser beam incident on one end surface of the optical fiber 14 The amount of incident beam 7 is limited.

A photodiode 15, which is a photoelectric conversion element, is arranged on the other end face of the optical fiber 14. Slit 13
The laser beam 7 that has passed through is photoelectrically converted by a photodiode 15, and current-voltage converted by an operational amplifier 16 and a feedback resistor Rf17. The voltage level of the output signal of the operational amplifier 16 as a detection signal is compared with the reference voltage 19 by the comparator 1B, and the output signal is the reference voltage 19.
When the potential is higher, a BD (beam position detection signal) 11 is output from the comparator 18.

The signal BDII is sent to a control section (not shown), and at the same time is inputted to the trigger input terminal of the timer circuit 20 and the data input terminal of the latch circuit 23.

The timer circuit 20 starts timing operation at the rising edge of the signal BDII, and resistor R21 and capacitor C2
The end time t of the timing operation is determined by the time constant determined in step 2.
0 is determined. The timer circuit 20 then outputs a timing signal TM from the output terminal Q. This timing signal TM is input to the trigger input terminal of the latch circuit 23. The latch circuit 23 performs a data input latching operation at the rising edge of the timing signal TM, and outputs an error signal ERR from the output terminal Q when the BD signal 11 is at H (high) level.

Next, the operations of the m first fruits will be explained in more detail with reference to FIGS. 3 and 4.

FIG. 3 shows the relationship between the beam diameter of the laser beam 7 and the detected waveforms output from the slit 13 and the operational amplifier 16. (A) in this figure shows the state when the normal laser beam A is scanned. When the laser beam A moves at a constant speed to the position A', the light intensity distribution of the laser beam A and the slit Due to the relationship between the aperture areas 13 and 13, a detected waveform as shown by C is obtained from the output end of the operational amplifier 16. On the other hand, (B) of this figure shows the state when the laser beam B, whose beam diameter has expanded due to optical distortion or failure of the laser diode, is scanned.
As in case A), when the laser beam B moves at a constant speed to the position B', a detected waveform like D is obtained from the output terminal of the operational amplifier 16.

Here, comparing the detection waveforms in (8) and (B), the areas of the two detection waveforms C5D obtained from the operational amplifier are constantly controlled to a predetermined amount or the amount of light emitted by the laser diode, so they are approximately equal. , when the laser beam B with a wide complete distribution of the laser beam is scanned, the slit 1
3, the time during which the laser beam is incident becomes longer.

That is, in FIG. 3, the time tl and h during which light exceeding a predetermined amount of light (above the broken line T in the figure) is incident on the slit 13 is 1. <12. Therefore, by making the value of the reference voltage (E) 19 in FIG. 2 equal to the level of the broken line TH in FIG. 3, the signal B as shown in FIG.
D is obtained from comparator 18.

(8) in Figure 4 shows the signals BD, TM and ER when the normal laser beam A is scanned in (^) in Figure 3.
CB in FIG. 4 shows the output state of the signals BD, TM, and ERR when the abnormal laser beam B with a wide beam diameter in FIG. 3 (B) is scanned. . As described above in FIG. 3, the on time (effective output time) of the signal BD is not shown by [l and t2]. The timer circuit 20 starts measuring time in response to the rising edge of the signal BDII, and operates the mono-multivibrator only for a fixed time t0 determined by the time constant of the resistor R21 and the capacitor C22, thereby generating a waveform as shown in FIG. outputs a timing signal TM.

The above time L0 is set as an allowable range of laser beam diameter that can be recognized as normal (i.e., a normal beam diameter range),
The signal B11 is latched by the latch circuit 23 at the rising edge of the signal TM. In Figure 4,
Since ti<to<h, the error signal ERR is generated from the latch circuit 23 in the case of (B) in FIG.

Furthermore, in the above embodiment, the error signal ERR is generated only when the laser beam diameter widens, but the mono-multivibrator operating time t' of the timing signal TM is adjusted in consideration of the minimum required beam diameter. t゛. By setting <ti, abnormal narrowing of the laser beam diameter may be detected, and by connecting the two detection means described above in parallel, thickening or thinning of the laser beam diameter can be detected simultaneously. It may be configured as follows.

In the first embodiment described above, an abnormality in the laser beam diameter was detected by measuring the time taken for the laser beam to pass through the slit 13. It is possible to detect abnormalities in the laser beam diameter.

FIG. 7 shows a circuit configuration of a second embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals.

As shown in FIG. 7, the laser beam incident on the photodiode 15, which is a photoelectric conversion element,
The signal is photoelectrically converted by the operational amplifier 16 and the feedback resistor 17, and then current-to-voltage converted by the operational amplifier 16 and the feedback resistor 17. The output signal (detection signal) of the operational amplifier 16 is input to the comparator 18, and at the same time, is input to the differentiating circuit composed of a capacitor C824 and a resistor R125. The level of the output signal of this differentiating circuit, which indicates a change in the amount of incident laser beam light, is compared with a reference potential E1 indicated by 26 by a comparator 27,5. US potential E.

In the case of a higher potential, the signal DC from the comparator 27
T is output. The output No. 48 DC,T is latched by the latch circuit 30 at the previous stage, and the signal LCT is output from the latch circuit 30.

The detection signal input from the operational amplifier I6 to the non-inverting input terminal (positive terminal) of the comparator J8 is sent to the comparator 18.
The signal B is sliced and waveform-shaped by the reference potential E.
It is output as D. At the falling edge of the signal nD, the latch circuit 31 at the subsequent stage performs the above-mentioned 4tcr latch operation, and after a slight delay through the delay circuit (delay element) 2g, the signal BD is applied to the clear terminal of the latch circuit 30, and the latch circuit 30 clear operations are performed.

FIG. 8 shows the timing of the output signal in the second embodiment, where (A) shows a case where a normal laser beam is incident on the photodiode 15, and (B) shows a case where a laser beam with a wide beam diameter is applied. The case where the light is incident on the photodiode 15 is shown. In the normal state shown in FIG. 8A, the rise of the detection signal waveform (detection waveform) of the operational amplifier 16 is fast, so the potential level of the differential waveform output by the capacitor C824 and resistor R325 of the differential circuit becomes larger than the reference potential E1 of the comparator 27, the signal OCT is generated from the comparator 1 notor 27, and the latch circuit 30 operates using this No. 43 DCT as a trigger force (to generate the S No. LCT. so that the signal B[l
Since the latch circuit 31 latches the signal LCT at the falling edge of , the error signal ERR is not generated from the latch circuit 31 at the subsequent stage.

On the other hand, in the case of the abnormal state shown in FIG. 8(B), the rise of the detection signal waveform (detected waveform) of the operational amplifier 16 is slow, so the differential waveform of the differentiating circuits 24 and 25 does not reach the reference potential E1. . Therefore, the comparators 27)
T is not generated, the latch operation of the latch circuit 30 at the previous stage is not performed, and the signal LCT is not generated from the latch circuit 30. Therefore, the latch circuit 31 at the subsequent stage generates the error signal ERR at the falling edge of the signal BD.

[Effects of the Invention] As explained above, according to the present invention, the effective output time of a signal output from the light beam detection means for detecting a horizontally scanned light beam is measured, and the effective output time is set as a reference. The error code is output by comparing it with a predetermined time, or by detecting the amount of change in the light intensity of the signal output from the light beam detection means using a differential circuit and comparing it with a reference value. It is possible to easily determine an abnormality in the beam diameter of a beam such as a laser beam, and furthermore, it is possible to prevent deterioration of an output image.

[Brief explanation of the drawing]

1(A) and (B) are block diagrams showing the basic configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the circuit configuration of the first embodiment of the present invention, and FIG. 3 is a block diagram showing the circuit configuration of the first embodiment of the present invention. An explanatory diagram showing the relationship between the laser beam and the waveform of the detection signal (detection waveform) in the embodiment of FIG. 4 is a timing chart showing the timing of each signal in the embodiment of FIG. 2, and FIG. 5 is the configuration of the conventional example. FIG. 6 is a timing chart showing the signal timing of the conventional example, FIG. 7 is a circuit diagram showing the circuit configuration of the second embodiment of the present invention, and FIG. 8 is a practical example of FIG. 7. 3 is a timing chart showing the timing of each signal in FIG. 2... Laser unit, 5... Rotating polygon mirror, 6... Imaging lens, 13... Slit, 14... Optical fiber, 15... Photodiode, 16... Operational amplifier, 17... Feedback resistor, 18.27... Comparator, 20... Timer circuit, 23JO, 31... Latch circuit, 24.25... Differential circuit. 1st missing column θ times details 1 without page 2nd figure a: l -m''``'f Explanation Giant 3rd Eye (B) Ichimu Nodo - High Shadoki Princess with the inferior Koivu] 1 - ShiL Salmon ＼ku wo kakakobu stab - 27r also Ll Ko, fX U.S. Igeri 0 Thailand S Nkhunayat Diagram 6 Procedural Amendment July 11, 1986

Claims (1)

[Scope of Claims] 1) A light beam scanning device having a light beam scanning means for forming an image by scanning a light beam and irradiating the photoreceptor with the light beam, comprising: a light beam detection means for detecting the light beam; Comparing means for comparing the level of the detection signal of the light beam detecting means and the reference voltage, and measuring the output time of the output signal of the comparing means and generating an error signal if the output time is outside a predetermined allowable time range. 1. A light beam scanning device comprising: a timekeeping means for outputting a time. 2) A light beam scanning device having a light beam scanning means for forming an image by scanning a light beam and irradiating it onto a photoreceptor, comprising: a light beam detection means for detecting the light beam; and a detection means for the light beam detection means. A differentiating circuit that differentiates the signal, and a level comparison between the output signal of the differentiating circuit and a reference voltage,
A light beam scanning device comprising: comparison means for outputting an error signal when the output signal does not reach the reference voltage.