JP2002062495A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which eliminates the need for detecting operation carried out by repeatedly driving a lens and can greatly shorten the time needed to correct a beam to a proper beam diameter. SOLUTION: A detecting means 10 has two optical sensors Sa and Sb provided on a common base 20 at an interval ΔX in the image height direction (arrow X in Fig.). The shape of an ideal depth curve is previously stored as a table in a memory of a control part 13. The optical sensors Sa and Sd measure beam diameters da' and db' respectively and they are and compared with the previously stored table of the depth curve to compute the waist position where the beam spot diameter become smaller; and the driving quantities of correcting lenses 3 and 4 are calculated from the difference from an image plane position to move them. For confirmation, the optical sensors Sa and Sb measures again the beam spot diameters to judge whether or not they are proper and if they are slightly different, the operation is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer and a digital copying machine, and a measuring instrument,
The present invention relates to an optical scanning device such as a laser beam scanning optical device incorporated as an image printing unit in an inspection device.

[0002]

2. Description of the Related Art In recent years,
In order to improve image quality, a laser beam scanning optical device that is incorporated as an image printing unit in a laser printer, a digital copying machine, or the like is required to be capable of printing at high density. For this reason, the spot diameter of the laser beam on the surface to be scanned (photoreceptor) becomes smaller, and the allowable depth of focus becomes smaller. In such devices, changes in the environment, in particular,
If the optical device generates heat during use and the optical element and its holder undergo thermal expansion, the focusing position shifts in the front-back direction of the surface to be scanned, and the beam spot diameter is so large that it is unacceptable to maintain high image quality. Problem had arisen.

As a technique for coping with such a problem, as disclosed in Japanese Patent Application Laid-Open No. 2-58016, a laser beam condensing state is detected at an optically equivalent position with respect to a photosensitive member. There is a method of correcting a beam focusing position by moving a focusing lens.

Recently, however, the scanning speed of the beam spot has become extremely high as the printing speed is set to a high speed, and the response speed of the detection circuit is increased in the conventional beam condensing state detecting means. Must be
It is necessary to use an element having a high-speed response that can sample the output of the light receiving element at intervals of the order of MHz and GHz, which has led to an increase in cost.

Therefore, in the technique disclosed in Japanese Patent Application Laid-Open No. 10-20225, a laser light source is made to emit a pulse at a fixed point, and the focused state of the pulse beam is detected. The focusing state of the laser beam can be detected by the detecting means with a simple configuration, and the optical element is driven based on the focusing state detection result to adjust the focusing position of the laser beam, thereby always obtaining a high-quality image. Have to be able to.

However, pulse light emission is premised on the detection of the image formation state of the light beam. However, in actuality, the timing of pulse light emission is shifted to lower the detection accuracy, and since the knife edge method is used, main scanning is performed. There is a problem that the imaging state of the light beam in the sub-scanning direction can be detected, but the imaging state of the light beam in the sub-scanning direction cannot be detected. It should be noted that the inventors of the present application know that in the prior art, the main scanning direction,
There is no example of technology that independently detects the sub-scanning directions. There is also a problem that a synchronous detection element is required to control the write timing in the main scanning direction.

Therefore, the imaging state can be detected independently in both the main and sub scanning directions with a simple mechanism, and the detection signal output from the light beam detection device is used as a synchronization signal, so that the synchronization detection element can be used. The present applicant has proposed a device that can obtain a synchronization signal without providing a separate device.

In this technique, since the slits are conventionally arranged perpendicular to the main scanning direction, the imaging state of the light beam in the main scanning direction can be detected, but the imaging state of the light beam in the sub-scanning direction can be detected. In consideration of this, as shown in FIG. 1, a photodiode (hereinafter referred to as P
D) The slit-shaped opening formed on the upper side is a triangular opening 20 as shown in the figure, one side 20a of which is perpendicular to the main scanning direction as before, and the other side 20b is the main scanning direction. In addition, the light beam is tilted so as to be inclined with respect to any of the sub-scanning directions, so that both the image forming states of the light beam in the main and sub-directions can be detected.

That is, when the light beam P scans over the opening 20, an output waveform as shown in FIG. 2 is observed. Light beam P
The side 20a perpendicular to the moving direction of the oblique side 20 in the main scanning direction
b indicates an output in the sub-scanning direction, and the size of the spot of the light beam P is detected by detecting the temporal speed at which this detection signal rises. Then, the size of the beam spot is finally determined by differentiating the output signal and detecting the peak value to determine the rising speed. In FIG. 2, the output of the light beam P indicated by a solid line in FIG. 1 is indicated by a solid line, and the output of the light beam P ′ indicated by the broken line is indicated by a broken line.

That is, in these prior arts,
The size of the beam spot on the image plane is detected and obtained by one light receiving sensor installed at a position equivalent to the image plane of the photoconductor. However, in such a system, the size of the beam on the image plane can be known by the detection unit, but if the size is not appropriate, the position of the lens system in the optical path is varied for correction. Action is required.

That is, in order to obtain the relationship between the position of the lens and the size of the beam diameter as shown in FIG. 3, the operation of the flowchart of FIG. 4, particularly the loop operation of steps 1 to 3 in the flowchart, is frequently performed. Must-have.

Referring to the flowchart of FIG. 4, the beam diameter is measured (step 1), stored in a memory, and the lens is minutely driven (step 2) to determine whether a depth curve as shown in FIG. 3 has been drawn. Is determined (step 3), and if not drawn, a loop operation returning to step 1 is performed. If drawn, the amount of movement of the lens is calculated based on the data stored in the memory (step 4), and the lens is moved based on the calculation result. Is moved (Step 5), the beam diameter is measured (Step 6), and it is determined whether the beam diameter is appropriate (Step 7). If not, the process returns to Step 1; I do. That is, the lens movement operation (step 2) and the beam detection operation (step 1) must be repeatedly and frequently performed, and it takes a very long time to perform the beam correction operation and at the same time consumes energy to drive the circuit. There are two problems with increasing amounts.

Accordingly, the present invention does not require the operation of repeatedly driving and detecting the lens, and can greatly reduce the time required to correct the beam to an appropriate beam diameter. Therefore, the beam is corrected more frequently than before. It is an object of the present invention to provide an optical scanning device capable of improving the quality of an image, reducing the amount of power consumed for detection and driving a lens, and obtaining an energy saving effect.

[0014]

In order to achieve the above object, an optical scanning device according to a first aspect of the present invention transmits light emitted from a light source to a surface to be scanned via a deflecting means and an imaging element. A scanning optical system for scanning, a detecting unit for detecting an image forming state of light scanned by the scanning optical system, an adjusting unit for adjusting the image forming state of the detected light, and an output from the detecting unit. And a control means for controlling the adjustment means, wherein the detection means comprises at least two or more detection units.

According to a second aspect of the present invention, in order to achieve the above object, the two or more detecting means are provided on the same base.

According to a third aspect of the present invention, in order to achieve the above object, an element for splitting light emitted from the light source is provided.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 is an overall configuration diagram (A) showing an embodiment of the optical scanning device according to the present invention, and a configuration diagram (B) of a detection unit. In the figure, 1 is a laser light source, 2 is a coupling lens, 3 and 4 are correction lenses, 5 is a deflector, 6 is an image forming element, 7 is a photosensitive member which is a surface to be scanned, and is a correction lens 3 in the main scanning direction. The focal position is adjusted, and the focal position in the sub-scanning direction is adjusted by the correction lens 4. In the figure, reference numeral 10 denotes a detecting device for detecting an image forming state of a light beam. 11 and 12 are mechanisms for moving the correction lenses 3 and 4 in the optical axis direction, respectively, and 13 is a control unit.

In this detecting means 10, two optical sensors Sa and Sb are provided on a common base 20 to reduce the number of parts and reduce costs. These optical sensors Sa and Sb are set apart from each other by ΔX in the image height direction (the arrow X direction in the figure). In the defocus direction (arrow Z direction in the figure), Z0 is an image plane position, Za and Zb are la and lb distances from the image plane position Z0, respectively, the optical sensor Sa is at the position Za, and the optical sensor Sb is at the position. Zb. As the optical sensors Sa and Sb, known means suitable for detecting the beam diameter may be used. For example, there is a type that can detect an imaged state of a light beam by itself, or a type in which a slit-shaped or triangular-shaped opening is provided on the front side in a light-receiving direction so that a beam diameter can be detected.

FIG. 6 is a diagram showing an example of how much the lens should be moved when the ideal depth curve C moves to A due to a temperature change or the like. FIG. Is shown in the flowchart of FIG. First, since the shape of the depth curve hardly changes even when the temperature changes, this curve is stored in a table in the memory of the control unit 13 in advance. Then, the beam diameter da 'is measured by the optical sensor Sa at the position Za and stored in the memory (Step 1). Next, the beam diameter db' is measured by the optical sensor Sb at the position Zb and stored in the memory (Step 1). 2) Compute the waist position (the position in the Z direction at which the beam spot diameter becomes the smallest) Zp by comparing the measured beam spot diameters da ′ and db ′ with a depth curve table that has been stored in advance, and calculate the image plane position. The amount of lens drive is calculated from the difference ΔZ from Z0 (step 3),
The lens is moved based on the value (step 4).
Then, for confirmation, the beam spot diameter is measured again by the optical sensors Sa and Sb (steps 5 and 6), and it is determined whether or not the beam diameter is appropriate (step 7). If the processing is slightly different, the process returns to step 1 and the same operation is repeated to correct the difference.

FIG. 8 shows an example in which the ideal depth curve C moves to B, but the above-described method is the same as the correction operation.

That is, in any case, the loop operation of steps 1 to 3 in FIG. 4 becomes unnecessary, the beam detection operation is performed promptly, the beam can be corrected without hindering the use of the user, and the time required for the correction can be reduced. Since the length is short, the beam can be frequently corrected, and the accuracy of the beam correction is improved. For this reason, power consumed for driving the optical sensor and driving the lens is saved, and the energy saving effect is enhanced.

FIG. 9 shows the optical sensors Sa, Sb, Sc, S
FIG. 11 shows a detection unit according to a second embodiment of the present invention in which five d and S0 are provided, and the beam spot diameters at five different positions in the defocus direction Z are measured as shown in FIG. As shown in the figure, 5 different positions in the defocus direction Z
When the beam spot diameter of a point is measured, the accuracy is improved as compared with a case where two optical sensors are used to predict the beam waist position Zp. Of course, the greater the number of optical sensors, the better the accuracy.

However, when a plurality of optical sensors are installed,
Because the position of each optical sensor in the X direction is far away,
The waist position may be slightly different in each optical sensor, and the influence may slightly affect the correction accuracy of the beam spot diameter. Originally, the position where each optical sensor is installed is a position where image formation is not performed, so there is such a subtle difference in the waist position. Although it is possible to design a scanning lens that does not have such a difference by designing the scanning lens, it is not preferable because the lens becomes large and the manufacturing cost increases.

FIG. 11 shows a detecting means according to a third embodiment of the present invention having a structure which is not affected by the slight difference in the waist position. That is, in the present embodiment, the optical sensor S
The light incident on a is split into two luminous fluxes by a splitting element 21 (a beam splitter, a half mirror, etc., whether a cube type or a flat type) placed in front of the optical sensor Sa,
The light is incident on both the optical sensors Sa and Sb. At this time,
The optical sensor Sa is at the position Za, and the optical sensor Sb is at the position Z.
Install at a position equivalent to b. Naturally, detection is performed at an appropriate position in the Z direction in consideration of the optical characteristics such as the refractive index of the splitting element 21.

With the above configuration, the characteristics of the beams detected by the optical sensors Sa and Sb are exactly the same in the image height direction (X direction), and are not affected by the shift of the waist position, thereby improving the accuracy of beam detection. As a result, the accuracy of beam correction is improved. Further, the angle of view of the light scanned by the scanning lens can be narrowed, the size of the scanning lens can be reduced, and the development cost can be reduced.

[0026]

According to the optical scanning device of the first aspect of the present invention, as described above, the detecting means for detecting the imaging state of the light scanned by the scanning optical system includes at least two or more detecting units. This eliminates the need to repeatedly drive the lens to perform detection, greatly reducing the time required to perform the operation of correcting the beam to an appropriate beam diameter, and therefore performing beam correction more frequently than before. This makes it possible to improve the quality of the image, reduce the amount of power consumed for detection and driving the lens, and obtain an effect of saving energy.

According to the optical scanning device of the second aspect of the present invention, as described above, two or more detecting means are provided on the same base. In addition, there is an effect that the number of parts can be reduced by sharing the base, and the cost of the apparatus can be reduced accordingly.

As described above, the optical scanning device according to the third aspect of the present invention includes the element for splitting the light emitted from the light source, and the light having the same image height can be split and guided to two sensors. Therefore, in addition to the same effects as those of the apparatus according to claim 1 or 2, there is no need to consider a difference in waist position due to a difference in image height in order to detect a shift in beam waist position. There is an effect that accuracy is improved and high quality image quality can be obtained. Further, the angle of view of light scanned by the scanning lens can be narrowed, so that the scanning lens can be reduced in size and the development cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a conventional optical scanning device.

FIG. 2 is a diagram showing a detection output obtained by the device of FIG. 1;

FIG. 3 is a diagram showing the relationship between the position of a lens and the size of a beam diameter.

FIG. 4 is a flowchart showing an operation necessary for obtaining a relationship between a position of a lens and a size of a beam diameter in FIG. 3;

FIG. 5 is an overall configuration diagram (A) showing an embodiment of the optical scanning device according to the present invention, and a configuration diagram (B) of a detection unit.

FIG. 6 is a diagram illustrating an example in which a necessary movement of a lens is obtained when an ideal depth curve moves.

FIG. 7 is a flowchart of an operation for performing the lens movement of FIG. 6;

FIG. 8 is a diagram illustrating an example in which a necessary movement of a lens is obtained when an ideal depth curve moves to a position different from that in FIG. 6;

FIG. 9 is a diagram illustrating a detecting unit according to a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a detection position of a detection unit of the embodiment of FIG. 9;

FIG. 11 is a diagram illustrating a detecting unit according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Coupling lens 3, 4 Correction lens 5 Deflector 6 Imaging element 7 Photoreceptor which is a surface to be scanned 10 Means for detecting the imaging state of a light beam 11, 12 Move correction lens in the optical axis direction Mechanism 13 Control unit 20 Base 21 Split element Sa, Sb, Sc, Sd, S0 Optical sensor X Image height direction Z Defocus direction Z0 Image plane position Za, Zb position Zp Beam waist position

Continued on the front page F term (reference) 2C362 AA20 AA26 AA28 AA29 AA35 AA48 2H045 AA01 CA88 CA98 CB22 CB24 DA02 DA41 5C072 AA03 BA03 BA06 HA02 HA08 HA10 HA13 HB08 HB10 HB20 RA11 XA01 XA05

Claims (3)

[Claims] 1. A scanning optical system for scanning light emitted from a light source onto a surface to be scanned via a deflecting unit and an imaging element, and a detecting unit for detecting an imaging state of light scanned by the scanning optical system. An optical scanning device comprising: an adjusting unit configured to adjust an imaging state of light to be detected; and a control unit configured to control the adjusting unit based on an output from the detecting unit. An optical scanning device comprising at least one detection unit. 2. The optical scanning device according to claim 1, wherein said two or more detecting means are provided on the same base. 3. The optical scanning device according to claim 1, further comprising an element for splitting light emitted from the light source.