JP2761723B2 - Scanning optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scanning optical device that scans a laser beam,
In particular, the present invention relates to a scanning optical device capable of detecting and correcting a defocus of a laser light imaging spot caused by an environmental change such as a temperature.

(Prior Art) In recent years, devices such as a laser beam printer that scans a laser beam and forms a latent image on a photoconductor by blinking the laser beam to record a desired image have been widely known. I have.

FIG. 5 shows a schematic configuration of a laser scanning unit 100 for scanning a laser beam in this type of apparatus. When a laser beam is scanned by the laser scanning unit 100, first, a light emission signal generator is generated based on an input image signal.
101 causes the solid-state laser element 102 to blink at a predetermined timing. The laser light emitted from the solid-state laser element 102 is converted into a substantially parallel light beam by a collimator lens system 103, and furthermore, a rotating polygon mirror that rotates in the direction of arrow b.
104 f [theta] lens group 1 while being scanned in the arrow c ₀ direction by
05a, 105b, and 105c form a spot image on the surface to be scanned 106 such as a photosensitive drum.

An image-scanning exposure distribution is formed on the scanned surface 106 by the scanning of the laser light, and the scanned surface 106 is scrolled by a predetermined amount perpendicular to the scanning direction for each scan. Thus, an exposure distribution according to the image signal is obtained on the scanned surface 106. Then, by printing this latent image on recording paper by a well-known electrophotographic process, a high-density image can be obtained.

(Problems to be Solved by the Invention) In such a conventional example, in order to perform high-density recording by using a latent image formed on a photoconductor, the surface to be scanned 10
It is necessary to reduce the size of the spot irradiated on 6 according to the density to be recorded. For example, when a Gaussian spot that blinks for each pixel is scanned, the exposure distribution on the surface to be scanned 106 changes as shown in FIG. That is, when the spot diameter in the main scanning direction is small, the exposure distribution by the laser light is close to a rectangular wave matched to the blinking timing and the contrast is high, but as the spot diameter increases, the laser light penetrates into adjacent pixels, and Since the amplitude of the distribution is small and the contrast is low, the quality of the output image is degraded. Therefore, for example, when configuring a printer with a high resolution of 800 dpi (32 dots / mm), the contrast is set to 80.
%, The size of the spot formed on the photoreceptor must be suppressed to about 40 μm (Gaussian distribution spot, 1 / e ² diameter) or less.

On the other hand, in order to obtain a laser spot having such a small diameter, an imaging optical system having a large F / N is generally required, but when the value of F / N increases, the depth of focus of the imaging optical system increases. Is very shallow. For example, in an apparatus capable of scanning an imaging spot having a diameter of 40 μm in the main scanning direction, the focal position of the imaging optical system is set to the scanning surface 106.
Must be kept within a very small range of ± 0.8 mm before and after.

However, when a scanning optical system such as the above-described conventional example is actually configured, the members constituting the optical system undergo thermal deformation due to a change in environmental temperature, and the focal plane moves beyond the focal depth. The spot diameter may be larger than a desired value. In such a case, in the above-described conventional example, since the positions of the respective members are fixed, the contrast on the scanned surface 106 is reduced, and the image quality when forming an image is deteriorated. Had problems.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to prevent a shift of an imaging position due to a change in an environmental temperature and to accurately scan a laser beam. Another object of the present invention is to provide a simple scanning optical device.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, a light source that emits laser light, a collimator lens that collimates laser light emitted from the light source, and a light source that passes through a collimator lens A photoelectric conversion element that receives the laser light of
Adjusting means for adjusting the position of the collimator lens in the direction of the optical axis in accordance with the output of the photoelectric conversion element. The position of the collimator lens is adjusted according to the difference between the maximum output value and the minimum output value of the conversion element.

(Operation) In the present invention having the above-described configuration, when the laser beam that blinks according to the image signal is received, the maximum output value and the minimum output value of the output value output by the photoelectric conversion element receiving the laser beam are received. By adjusting the position of the collimator lens so as to have an appropriate spot diameter according to the difference between the output values, even when the size of the spot on the surface to be scanned changes due to environmental fluctuation, the size can be adjusted to a desired size. .

(Example) Hereinafter, the present invention will be described based on an illustrated example.

FIG. 1 shows a schematic configuration of a first embodiment of the scanning optical apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a light emission signal generator for generating laser light, and a solid-state laser element 2 as a laser light source connected to the light emission signal generator blinks according to the light emission signal. Reference numeral 3 denotes a collimator lens system that converts a laser beam emitted from the solid-state laser element 2 into substantially parallel light, and can be moved by a predetermined amount in a direction of an arrow A, which is an optical axis direction of the laser beam, by a focus adjusting unit 4 described later. ing. Reference numeral 5 denotes a rotary polygon mirror which, when rotated at a constant speed in the direction of arrow B, reflects parallel light emitted from the collimator lens system 3 and scans in the direction of arrow C. Reference numerals 6a, 6b, and 6c denote fθ lens groups provided in front of the rotary polygon mirror. The fθ lens group forms an image of the laser beam deflected by the polygon mirror 6 and makes the scanning speed uniform on the surface to be scanned. L is a laser beam, and this laser beam L is guided via a reflecting mirror 7 onto a CCD (solid-state imaging device) 8 as a detecting means, and is scanned on a photosensitive drum 9 as a surface to be scanned. The CCD 8 is configured by arranging a large number of photodetectors in the direction of the arrow C at positions optically equivalent to the surface of the photosensitive drum 9, and controls the generation signal generator 1 and the focus adjustment means 4. Connected to Around the photosensitive drum 9, a developing device (not shown), a primary and transfer charger, a fixing device, a cleaner, and the like are provided. The image is formed and transferred to a transfer material.

In the above-described configuration, when a desired image is formed, first, the image signal S is input to the light emission signal generator 1, and the solid-state laser element 2 blinks at a predetermined timing. The laser light emitted from the solid-state laser element 2 is converted into substantially 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 the fθ lens groups 6a, 6b, 6c forms an image on the photosensitive drum 9 in the form of a spot.

Then, an exposure distribution for image-scanning is formed on the surface of the photosensitive drum 9 by such scanning of the laser beam L,
Further, the photosensitive drum 9 is rotated by a predetermined amount for each scan to form a latent image having an exposure distribution according to the image signal S on the drum 9 and is recorded as a visible image on a recording sheet by a well-known electrophotographic process.

By the way, when forming a high-density image by forming the laser beam L into a minute spot on the photosensitive drum 9 by the optical system as shown in FIG. 1, the focal depth becomes extremely shallow as described above. Is well known. Accordingly, the members constituting the optical system are thermally deformed due to environmental temperature changes such as heat generation during laser light emission, and the solid-state laser element 2
When the distance between the laser beam L and the surface of the photosensitive drum 9 changes, the image point of the laser beam L deviates from within the depth of focus, and the beam spot diameter increases. As shown in FIG. It may deteriorate.

Therefore, in the present embodiment, when a shift occurs in the image point of the laser beam L, the adjustment is performed. That is, first, the generated signal generator 1 generates a rectangular wave that is turned on and off at a constant interval as shown in FIG. 2A for a predetermined period, and the solid-state laser element 2 blinks according to this signal. The laser beam from the solid-state laser element 2 is scanned as described above and reflected by the reflecting mirror 7, and the CCD 8 disposed at a position optically equivalent to the photosensitive drum 9.
Projected and scanned on.

Before the laser beam L scans on the CCD 8, the control unit 10
The charge stored in each pixel of the CCD 8 is reset, and after the charge is stored in each pixel of the CCD 8 by spot scanning of one line, this charge is read out as an electric signal.

When the laser beam from the solid-state laser element 2 blinks and is scanned once, the CCD 8 is located at a position optically equivalent to the photosensitive drum 9, so that the exposure distribution on the CCD 8 surface is as shown in FIG. The distribution shape of the intensity according to the spot diameter is shown. Therefore, the output of each pixel of the CCD 8 has a distribution as shown in FIG. 2B, and the signal is sent to the control unit 10. The control unit 10 sets the contrast V as the maximum value θ _max and the minimum value θ _min of the output of the CCD 8. Calculate and measure according to the formula.

In this case, as the spot diameter in the scanning direction becomes smaller, the contrast V becomes larger.
When V is smaller than a predetermined value as compared with V calculated by the formula, a drive signal is sent from the control unit 10 to the focus adjustment unit 4 to move the collimator lens system 3 in the direction of arrow A by a predetermined amount. . Then, the contrast V is measured at the position where the collimator lens system 3 is moved, and the collimator lens system 3 is fixed at the position where this value is the maximum. The main scanning spot diameter can be minimized.

FIG. 3 is an enlarged view of the collimator lens system 3 provided with the focus adjusting means 4. As shown in the drawing, the solid-state laser element 2 is mounted on the mounting portion 41a of the holding member 41 having a substantially U-shaped cross section, and the collimator lens system 3 is moved in the holding portion 41b in the direction of arrow A which is the optical axis direction of the laser light. Hold slidably. A flange 22 is provided on the lower surface of the collimator lens system 3, and the flange 22 and the holding member 21 are connected by a piezoelectric actuator 43 having a piezoelectric element that expands and contracts in a long direction, that is, in the direction of arrow A according to the applied voltage. The piezoelectric actuator 43 is connected to the control unit 10 and is driven by a drive signal from the control unit 10.

When moving the collimator lens system 3 in the direction, that the arrow A ₁ direction piezoelectric actuator 43 is contracted, the laser beam emitted from the collimator lens system 3 because the distance between the collimator lens system 3 and the solid laser element 2 is shortened It becomes divergent light, and the focal position as the scanning optical system moves in a direction away from the fθ lens group 6c. On the other hand, when moving the collimator lens system 3 in the direction, that the arrow A ₂ direction piezoelectric actuator 43 expands, the collimator lens system in the reverse 3
Is converged, and the focal position moves in a direction approaching the fθ lens group 6c. Note that the collimator lens system 3 may be moved using a voice coil or the like instead of the piezoelectric actuator 43.

As described above, the laser beam L is imaged on the CCD 8 disposed at a position optically equivalent to the photosensitive drum 9, the spot diameter is detected, and the position of the collimator lens diameter 3 is determined based on the detection signal. With the adjustment configuration, it is possible to prevent the laser spot diameter from increasing due to environmental fluctuations such as temperature. As a result, a spot of a desired size can always be obtained, and a high-density and high-quality image can be formed.

FIG. 4 shows a second embodiment of the scanning optical apparatus according to the present invention, and the same parts as those in the first embodiment are denoted by the same reference numerals. In other words, when the change in the spot diameter on the photosensitive drum 9 is mainly due to the change in the interval caused by the change in the environmental temperature between the solid-state laser element 2 and the collimator lens system 3, the collimator lens system 3 as in this embodiment is used. If the change in the laser light between the laser beam and the rotary polygon mirror 5 is detected, it is possible to sufficiently prevent the spot diameter from being enlarged. In FIG. 4, reference numeral 21 denotes a beam splitter, which is disposed in the optical path of the laser light beam L converted into parallel light by the collimator lens system 3, and splits the laser light beam L into two light beams. Here, one light beam is not changed in direction but is
And the other light flux is focused on the CCD 23 via the condenser lens 22. In the present embodiment, when the distance between the solid-state laser element 2 and the collimator lens system 3 fluctuates, the size of the imaging spot on the CCD 23 also changes. Therefore, the laser obtained by monitoring the signal obtained by the CCD 23 The image point shift of light can be detected, and as a result,
As in the first embodiment, the laser beam L can be accurately scanned on the surface of the photosensitive drum 9. The other configuration and operation are the same as those of the first embodiment, and the description thereof will be omitted.

(Effects of the Invention) According to the present invention having the above-described configuration and operation, when a laser beam blinking according to an image signal is received, an output value output by the photoelectric conversion element receiving the laser beam is output. By adjusting the position of the collimator lens so that an appropriate spot diameter is obtained according to the difference between the maximum output value and the minimum output value, it is possible to prevent the laser spot on the scanned surface from becoming too large due to environmental fluctuations such as temperature. I can do it. Therefore, particularly when applied to an apparatus for forming an image using a photoreceptor as a surface to be scanned, there is an effect that a high-density image can be always formed without deteriorating the quality.

[Brief description of the drawings]

FIG. 1 is a schematic structural view showing a first embodiment of a scanning optical apparatus according to the present invention, and shows signals during an adjusting operation in the embodiment shown in FIGS. 2 (a) and 2 (b). (A)
Is a graph showing a signal from the light emission signal generator, and FIG.
FIG. 3 is a graph showing an output signal from a CCD, FIG. 3 is an enlarged vertical sectional view showing a mechanism for moving a collimator lens system for adjusting an imaging position, and FIG. 4 is a second embodiment of a scanning optical apparatus according to the present invention. The laser beam is transmitted to the CCD using a beam splitter located near the collimator lens system.
FIG. 5 is a schematic configuration diagram showing a conventional scanning optical device, and FIG. 6 is a graph showing a relationship between a laser beam spot diameter and an exposure distribution. DESCRIPTION OF SYMBOLS 2 ... solid-state laser element (laser light source) 3 ... collimator lens system 4 ... focus adjustment means 41 ... holding member 43 ... piezoelectric actuator 7 ... reflecting mirror 8 ... CCD (detection means) 9 ...... Photosensitive drum (scanned surface) 10 Control unit

Claims (1)

(57) [Claims] A light source for emitting laser light, a collimator lens for collimating the laser light emitted from the light source, a photoelectric conversion element for receiving the laser light after passing through the collimator lens, and an output of the photoelectric conversion element. Adjusting means for adjusting the position of the collimator lens in the optical axis direction according to the
Wherein the adjusting means adjusts the position of the collimator lens according to a difference between a maximum output value and a minimum output value of the photoelectric conversion element when a laser beam blinking according to an image signal is received. A scanning optical device, characterized in that: