JPH02296210A - Scanning optical device with autofocus mechanism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a scanning optical device that scans a light beam from a light source onto an irradiated object, and particularly to a scanning optical device that scans an object to be irradiated with a light beam from a light source. The present invention relates to a scanning optical device capable of detecting and correcting defocus of a focused spot.

[Prior Art] In recent years, laser beam printers (LBPs) have been widely used that record a desired image by scanning a laser beam and forming a latent image on a photoreceptor by flickering the laser beam. There is.

In such an LBP, in order to perform high-density recording, it is necessary to reduce the size of the beam spot irradiated onto the scanned surface of the photoreceptor in accordance with the density to be recorded.

For example, when scanning a Gaussian spot that flickers for each pixel, the exposure distribution on the scanned surface changes as shown in Figure 6 (however, the figure shows the output value from the CCD) according to the spot diameter on the scanned surface. do. In other words, when the spot diameter in the main scanning direction is small, the exposure distribution of the laser light is close to a rectangular wave that matches the blinking timing (the contrast is also high, but as the spot diameter increases, the laser light invades adjacent pixels). The amplitude of the exposure distribution will be small (and the contrast will be low), which will degrade the quality of the output image.

Therefore, for example, 800dpi (32dots/m
When constructing a high-resolution printer (m), it is necessary to increase the above contrast to 80% or more, but in order to do so, the size of the spot imaged on the photoreceptor should be 40u.
m (Gaussian distribution spot, 1/e2 diameter) or less.

On the other hand, in order to obtain a laser spot with such a small diameter, an imaging optical system with a small F-number is generally required, but as the F-number becomes smaller, the depth of focus of the imaging optical system becomes extremely shallow. For example, in a laser scanner device that can scan an imaging spot with a diameter of 40 μm in the main scanning direction, the focal position of the imaging optical system is set at ±0.
It must be kept within an extremely small range of 8 mm.

However, when a scanning optical system like the conventional example described above is actually constructed, each member constituting the optical system undergoes thermal deformation due to changes in environmental temperature, etc., and the focal position of the imaging optical system shifts to the above-mentioned position. By moving beyond the depth of focus, the spot diameter may become larger than the desired value. In such a case, in the conventional example described above, the position of each member is fixed, so the focal position or imaging position of the imaging optical system cannot be adjusted.
The contrast of the surface to be scanned becomes low and the image quality deteriorates.

Furthermore, the problem mentioned above is that even when the material of the laser optical system is changed from glass to PMMA-based open resin due to cost advantages, the refractive index of the resin changes due to moisture absorption, causing the imaging position to shift. So, it happened.

In order to prevent the image formation position from shifting due to such environmental changes and from degrading the image quality, a detection means is provided to detect the focus shift based on the scanning beam, and a focus shift correction lens is installed based on the signal from the detection means. Laser scanner devices have been proposed that are equipped with a so-called autofocus mechanism (AF mechanism) that moves in the optical axis direction to always align the image forming position of the image forming optical system on the photoreceptor (for example, Japanese Patent Application Laid-Open No. 1983-1999). 116603
(see publication).

In such conventional AF mechanisms, the laser beam spot diameter and laser beam spot light intensity on the surface of the photoconductor are guided to the photoelectric conversion element directly or using optical means such as lenses, optical fibers, and reflective mirrors. Based on the detected value, the correction lens and semiconductor laser element are moved using an actuator so that the focus of the laser beam matches the surface of the photoreceptor.

[Problem to be solved by the invention] However, if the position of the photoelectric conversion element or the optical means for guiding the laser light to the photoelectric conversion element moves due to vibrations or other causes, sufficient light may not reach the photoelectric conversion element. In addition, not only is the focusing operation not performed with high precision, but in the worst case, it becomes undetectable, and the image quality obtained from the laser beam printer is low quality (out of focus), sometimes inferior to conventional configurations without an AF mechanism. There is also.

Furthermore, in addition to the positional deviation of the defocus detection system! - The accuracy of defocus detection may decrease due to contamination of the optical system due to scattering of particles, particles, etc.

If the output from the photoelectric conversion element becomes small due to dirt in the optical system, not only will the defocus detection accuracy decrease, but also malfunctions will easily occur due to external noise. Poor image quality that is out of focus is likely to occur.

Therefore, an object of the present invention is to solve the above-mentioned problems (i.e., when it is determined that a sufficient defocus correction function cannot be achieved, the defocusing device is moved to a predetermined in-focus state and stopped there) An object of the present invention is to provide a scanning optical device having a configuration that allows

[Means for Solving the Problems] In the present invention for achieving the above object, a light beam from a light source such as a laser light source is focused and scanned on an irradiated object such as a photosensitive drum, and the irradiated object is A CCD that detects the convergence state of the light beam on the irradiated object based on the light beam scanned on the body
Based on the signal from this detection means, it is determined that the autofocus mechanism, which has a focus adjustment means such as a stepping motor that adjusts the focusing state, is unable to detect defocus sufficiently. In this case, the focus adjustment means brings the focus correction means such as the collimator lens system to a predetermined position such as a designed focus position and stops there.

The judgment that the focus shift detection cannot be performed satisfactorily is based on the fact that the focus shift detection means does not obtain a focus shift signal of a predetermined value or more even after the autofocus mechanism is operated a predetermined number of times, or the focus shift detection means detects an abnormality. If the signal is (e.g.
This is done when an extremely large signal is output.

[Function] According to the scanning optical device such as the LBP having the above configuration, if it is found that the AF mechanism cannot perform the intended function for some reason, the focus correction means is activated regardless of the defocus detection signal. (For example, collimator lens system or laser light source) is moved to the set position and stopped there, so AF
The mechanism does not make meaningless focal shift adjustments, and the focal position shift of the beam spot can be kept to a minimum.

[Embodiment] FIG. 1 shows a schematic configuration of an embodiment according to the present invention. In the figure, reference numeral 1 denotes a laser driver for generating laser light, and a solid-state laser element 2 as a laser light source connected to this laser driver 1 blinks in response to its light emission signal.

Reference numeral 3 denotes a collimator lens system that converts the laser beam emitted from the solid-state laser element 2 into substantially parallel light, and is movable within a predetermined range in the six directions of arrows, which are the optical axis directions of the laser beam, by a focus adjustment means 4, which will be described later. It becomes. A rotating polygon mirror 5 reflects and deflects the parallel light emitted from the collimator lens system 3 by rotating at a constant speed in the direction of arrow B to scan in the direction of arrow C. Reference numerals 6a, 6b, and 6c are f/θ lens groups provided in front of the rotating polygonal mirror 5, which form an image of the laser beam deflected by the polygonal mirror 5 and adjust the scanning speed to the photosensitive surface that is the scanned surface. The speed is constant on the drum 9.

The laser beam is guided onto a CCD (solid-state imaging device) 8 as a detection means through a reflecting mirror 7 outside the effective scanning area, and then scanned onto a photosensitive drum 9. The CCD 8 is configured by arranging a large number of photodetectors in the direction of arrow C at positions optically equivalent to the surface of the photosensitive drum 9, and is connected to an AF control section 10 that controls the laser driver 1 and the focus adjustment means 4. has been done.

A primary developing device, a transfer charger, a fixing device, a cleaner, etc. (not shown) are provided around the photosensitive drum 9, and a latent image formed on the surface of the photosensitive drum 9 by a laser beam is converted into a known electrophotographic image. The image is visualized through a process and transferred to a transfer material.

The AF control unit 1O adjusts the AF control at regular intervals based on signal changes from the temperature sensor 1 installed near the collimator lens system 3.
N, OFF square wave AF multiplied signal is output to the laser driver 1, and a laser beam beam for defocus detection is emitted from the laser element 2, and the signal from CC, D 8 and the signal from the temperature sensor 11 are output to the laser driver 1. Then, the focus adjustment means 4 is operated and controlled to adjust the focus shift.

The image processing section 12 outputs an image signal to the laser driver 1 according to a command from the main body operation section 13, and also outputs an image output signal indicating that this image signal is being outputted to the AF control section 10. This image output signal is output to the AF control section 10 before the image signal is output to the laser driver 1, and the output is stopped after the output of the image signal is finished.

While this image output signal is being manually input to the AF control section 10, the operation of the focus adjustment means 4 is stopped.

The main body operation section thus controls the image forming operation of the LBP via the image processing section 12, but instructions for the image forming operation are given by the operator operating an operation panel (not shown) of the operation section 13. It will be done.

Next, the focus adjustment means 4 and the conometer lens system 3 will be explained in detail with reference to FIG. In the figure, frame 41
A solid-state laser element 2, a stepping motor 42, and a guide shaft 45 are provided, and the collimator lens system 3 is movably supported in the optical axis direction by a lead screw 43a machined into the shaft 43 of the stepping motor 42 and the guide shaft 45.

One end of the shaft 43 on which the lead screw 43a is formed is supported by a bearing 44 fixed to the frame 41, and the collimator lens system 3 has a female screw (
A sliding bearing (not shown) that slides on the guide shaft 45 is provided on the opposite side m11.

Further, a limit sensor board 46 is provided under the collimator lens system 3, and limit sensors 46 are provided at both ends of the board for detecting the movement limit of the collimator lens system 3.
7.48 is provided. In this embodiment, the limit sensors 47 and 48 also serve as the home position of the collimator lens system 3.

In the focus adjusting means 4 having the configuration shown in FIG. 2, when the collimator lens system 3 moves in the direction of arrow A and its front end f comes onto the limit sensor 47, the stepping motor 42 reversely rotates to move the collimator lens system 3. The collimator lens system 3 starts to be moved in the direction of arrow A2, and is moved in the optical axis direction of the laser beam until the rear end portion is above the limit sensor 48. In this way, the stepping motor 42 is rotated by the AF control unit 10 based on the defocus detection signal from CC, D8, the collimator lens system 3 moves between the limit switches 47 and 48, and the defocus detection signal is The laser beam L is stopped at a position set by , and the laser beam L is focused on the photosensitive drum 9 .

In the above configuration, when forming a desired image, an image signal is first input to the laser driver 1, and the solid-state laser element 2 is made to blink at a predetermined timing. Solid state laser element 2
The laser beam emitted from the is converted into approximately parallel light by the collimator lens system 3, and further scanned in the direction of arrow C by the rotating polygon mirror 5 rotating in the direction of arrow B, and scanned in the direction of arrow C.
A spot image is formed on the photosensitive drum 9 by the 21 groups 6a, 6b, and 6c.

By scanning the laser beam (2), an exposure distribution for one image scan is formed on the surface of the photosensitive drum 9, and furthermore, the photosensitive drum 9 is rotated by a predetermined amount for each scan, and an image is distributed on the drum 9 according to the image signal. A latent image having an exposure distribution is formed, and this latent image is recorded as a visible image on recording paper by a well-known electrophotographic process.

Normally, images are recorded as they are, but if the various members that make up the optical system are thermally deformed due to environmental temperature changes due to heat generation from the laser element 2, etc., the focal point of the laser beam may be (When forming a high-density image, it is very shallow) As shown in Figure 5 (however, this figure shows the output value from the CCD 8), the contrast of the exposure distribution on the photosensitive drum 9 is low As a result, the image quality may deteriorate and the focus position may need to be adjusted.

Therefore, in this embodiment, in such a case, the temperature sensor 11 is used to detect when the temperature change in the environment near the optical system exceeds a set range, and the autofocus is activated to adjust the focal position of the laser beam. A sequence is set up. That is, the temperature sensor 1 immediately after the focus position adjustment is completed.
The signal value of 1 is always used as a reference temperature value and is rewritten to the previous value, and when the temperature changes from this reference temperature value by more than a set value, the focus position is adjusted again.

In this embodiment, a temperature range within which thermal deformation occurs within the depth of focus is used as a set value from the reference temperature value.

This focus position adjustment will be explained in detail below. When it is detected by the signal from the temperature sensor 11 that the environmental temperature has changed more than the set value, the AF control unit 10 changes as shown in FIG. 3(a).
An AF multiplied signal as shown in is outputted to the laser driver 1 for a certain period of time.

When the AF multiplied signal is manually input to the laser driver 1, the laser driver 1 causes the laser element 2 to emit light in a reduced amount in accordance with the AF multiplied signal rectangular wave. Such laser light from the laser element 2 is reflected by a reflecting mirror 7, and is projected and scanned onto a CCDg located at an optically equivalent position to the photosensitive drum 9. Here, the AF control unit 10 resets the accumulated charge of each pixel of CG and D8 before the laser beam scans the CCD 8, and resets the accumulated charge of each pixel of the CCD 8 after scanning the spot of one line. Read out the charge as an electrical signal.

When the solid-state laser element 2 flickers the laser beam as described above and scans once, the CCD 8 is located at an optically equivalent position to the photosensitive drum 9, so the exposure distribution on the surface of the CCD 8 is as shown in FIG. 6 above. It shows the distribution shape of the strength of the laser beam depending on the spot diameter. Therefore, the output of each pixel of the CCD 8 has a distribution as shown in FIG. 3(b), and the signal is sent to the AF control section IO. In the AF control section 10, the CCD
The maximum value of the output of 8 is θ. −1 minimum value θ. ,. As the contrast ■■=0□8-〇, 1n/θ, +1, 1x+θff1in
...-(1) Calculate and measure using the formula.

In this case, as shown in FIG. 6, the spot diameter in the scanning direction is small (so that the contrast V shown by the above equation (1) becomes large).

AF while the AF double signal is input to laser driver 1
The control unit 10 intermittently drives the stepping motor 42 (FIG. 2) to move the collimator lens system 3 back and forth in the optical axis direction at regular intervals, and measures the contrast (2) at each position. Then, when the maximum value of contrast (2) is obtained, the collimator lens system 3 is stopped, and focusing is performed by minimizing the spot diameter of the laser beam in the main scanning direction.

Here, the positions of the reflecting mirror 7, C, and CD 8 may shift due to vibrations, etc., and the laser beam may not be sufficiently guided to the CCD 8, or the scattered toner may adhere to the surface of the reflecting mirror 7 or CCD 8, causing the input light to the CCD 8 to Consider the case where the value decreases considerably.

In such a case, as shown in FIG. 5, the maximum output value from the CCD 8 will be close to or below the minimum value for AF detection, and the contrast will become extremely small at each position of the collimator lens system 3. The difference in contrast ■ becomes small, making it impossible to detect the in-focus position.

When such a state occurs, the present embodiment operates as shown in FIG. 4.

That is, first, when the output from the temperature sensor 11 changes beyond the set value', the AF is activated as shown in step 50.
The control unit 10 starts the AF operation as described above.

In this AF operation, if the defocus detection operation has not been performed continuously for the set number of times (n times) (step 51.N,
O) The sequence proceeds to step 52, where it is determined whether the AF detection signal from the CCD 8 is larger or smaller than the output value set as the minimum limit at the time of design (see FIGS. 5 and 6). Here, if the output value from the CCD 8 is smaller than the set value, the accuracy of the focus correction operation will decrease or it will become impossible to detect the focus shift, so the AF control unit 10 sends an AF signal to the laser driver 1. Subsequently, the n-1 parfocal shift detection operation is repeated until the output value from the CCD 8 reaches the set output value (step 52, No).

If the output value from the CCD 8 is greater than or equal to the set output value (step 52, Yes), the AF control unit 10 performs the focus correction operation as described above (step 53), and focuses the laser beam onto the photoreceptor 9. After matching and rewriting the signal value of the temperature sensor 11 at that time as the reference temperature value, AF is performed.
The operation is ended (step 54).

If a good output value is not obtained from the CCD 8 even after performing the n-1 parfocal shift detection operation (step 51. Yes)
After returning the collimator lens system 3 to the home position of the limit sensor 47 or 48, the AF control unit 10 adjusts the laser beam to the photoreceptor 6 based on the temperature signal value from the temperature sensor 11. The collimator lens system 3 is sent to the focused position r, and when the end face f of the collimator lens system 3 and the designed position r coincide, the operation of the stepping motor 42 is stopped (step 55). After moving the collimator lens system 3 in this manner, the AF control section 10 issues a warning indicating AF malfunction on the operation panel (not shown) of the main body operation section 13 (step 56), and ends the sequence (step 54). .

Incidentally, in the present invention, the defocus detection method for detecting the focused state of the laser beam spot and the focus adjustment means for aligning the focus of the laser beam L with the surface of the photoreceptor are arbitrary, and the above embodiments are (This is just an example.

For example, as a focus adjustment means, a piezoelectric element, a solenoid,
Various actuators such as stepping motors and DC motors, various mechanisms such as gears, cams, lid screws, etc. are used, and elements other than photoelectric conversion elements are also used as a defocus detection method.

In the method for starting A'F operation, it is not always necessary to use a temperature sensor as an environmental sensor to trigger AF operation based on changes in the environment (such as performing AF operation intermittently using a timer, or using LBP image output). It is also possible to perform AF operation intermittently based on the number of sheets.When using an environmental sensor, set values for several environmental points are set.
The AF operation may be started by comprehensively considering future detections.

In addition, the method of detecting the design position r described above uses known means such as optical, electromagnetic, etc. to obtain sufficient accuracy, and as in the above embodiment, once the design position r is returned to the home position, the collimator lens is Move the system etc. to obtain the design position,
The design position can be obtained by directly providing a detection mark or sensor at the design position.

[Effects of the Invention] As explained above, in the present invention, when it is found that defocus detection cannot be performed sufficiently (for example, even if the AF mechanism is operated a set number of times, the defocus detecting means detects a focus exceeding the set value). If a shift signal is not obtained), the focus adjustment means moves the focus correction means to the set position, which is the designed focus position, and stops, thereby eliminating the focus position shift of the laser beam spot due to malfunction of the AF mechanism. It has the effect of preventing to a minimum.

Further, even if the defocus detecting means does not function sufficiently due to dirt, vibration, etc., the minimum quality of the predetermined work that can withstand use (for example, image quality) can be maintained within the effective scanning area.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing one embodiment of the scanning optical device according to the present invention, Fig. 2 is an enlarged detailed view of the focus adjustment means and collimator lens system, and Fig. 3 is a signal during focal position detection operation. , (a) is a graph showing the waveform of the AF signal, (b) is a graph showing the output signal from the CCD 8,
Figure 4 is a sequence diagram of AF operation, and Figure 5 shows the relationship between the spot diameter of the laser beam and the exposure distribution during abnormal conditions.
FIG. 6 is a graph showing the output from the CCD 8 showing the relationship between the spot diameter of the laser beam and the exposure distribution under normal conditions.

Claims (1)

[Claims] 1. The light beam from the light source is focused and scanned on the irradiated object, and the condensation state of the light beam on the irradiated object is determined based on the light beam scanned on the irradiated object. In a scanning optical device equipped with an autofocus mechanism having a focus shift detection means for detecting a focus shift and a focus adjustment means for adjusting the focusing state based on a signal from the detection means, the focus shift can be detected sufficiently by the autofocus mechanism. A scanning optical device characterized in that, if it is determined that the focus correction means cannot be corrected, the focus adjustment means brings the focus correction means to a predetermined position and stops there. 2. According to claim 1, it is determined that defocus detection cannot be performed sufficiently if a defocus signal of a predetermined value or more is not obtained from the defocus detection means even after operating the autofocus mechanism a predetermined number of times. Scanning optics. 3. The scanning optical device 4 according to claim 1, wherein the predetermined position of the focus correction means is a designed focus position, and after the focus correction means is brought to the predetermined position, a warning indicating that autofocus is not activated is provided. 2. The scanning optical device according to claim 1, wherein 5. The scanning optical device according to claim 1, wherein the focus correction means is a collimator lens system. 6. Claim 1, wherein the irradiated object is a photoreceptor for image recording.
Scanning optical device as described.