JP2001221968A - Optical scanner, and focal adjustment method for optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner being capable of adjusting a focal position of a laser by the few number of times of detection. SOLUTION: The optical scanner has an optical scanning system imaging an emitted laser from a light source 1 on a body to be scanned 9 by a light deflection means 5 and an image formation element 6, a detecting means 7 detecting the image-formation state near the focal position of the laser L, focal position adjustment means 3 and 4 adjusting the image-formation state of the laser, and a control part 8 controlling the focal position adjustment means 3 and 4 based on detection of the detecting means 7. The control part 8 changes the focal position of Laser L to the focal position back and front to the detecting means 7, fetches two or more detection data with the different quantity of defocuses in each back and front of the focal position, and controls, on the basis of the two or more detection data, the focal position adjustment means 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device incorporated in a copying machine, a laser printer, and the like.

[0002]

2. Description of the Related Art For example, in an optical scanning device incorporated in a laser printer or the like, the spot diameter of a laser imaged on a surface to be scanned has been reduced for the purpose of improving image quality, and the depth of focus has been reduced. However, there is a problem that the optical element changes its shape due to a sudden change in the internal temperature when the power is turned on or when it is started for a long time, and it is not possible to obtain sufficient optical performance. Is provided.

FIG. 6 shows an overall configuration of a conventional optical scanning device, and a focus adjusting mechanism thereof will be described. The beam emitted from the light source 1 is scanned by the light deflecting means 5 via the collimator lens 2, the correction lens 3, and the mirror 9, and forms an image on the scanned object 9 by the condenser lens system 6.
The laser (two-dot chain line in the figure) deflected by the light deflecting means 5 is incident on the synchronous sensor 11 and the light receiving sensor 7 'by the mirror 10 at one end in the main scanning direction X.

The correction lens 3 is mounted on a moving stage 4, and the moving stage 4 is connected by a stepping motor 12 via a pinion and a rack.
2 is connected to the control unit 8 '. The control unit 8 'receives the output of the light receiving sensor 7' and drives and controls the stepping motor 12 based on the output of the light receiving sensor 7 '. As a result, the position of the correction lens 3 on the moving stage 4 is controlled back and forth in the optical axis direction of the laser, and the spot diameter of the laser on the scanned object 9 can be adjusted. That is, the laser defocus amount is controlled based on the output of the light receiving sensor 7 'to optimize the laser imaging state. Light receiving sensor 7 '
Is located at a defocus position substantially equivalent to the surface to be scanned of the object to be scanned 9. In this conventional example, a laser is focused on the light receiving sensor 7 'in the form of a light spot by a known knife edge method to determine the focal position. Therefore, the light emission of the light source 1 is controlled based on the laser detection by the synchronous sensor 11.

FIG. 7 shows a state where a laser beam is incident on the light receiving sensor 7 '. 3A shows a focused state, FIG. 3B shows a front focus state, and FIG. 3C shows a rear focus state. As shown in the figure, the light receiving sensor 7 'is divided into two parts, a sensor part A and a sensor part B, with the line lowered in the optical axis direction from the edge E as the center, and the light is emitted from each of the sensor parts A and B. The stored charge is output. In the front focus state, light reception is detected only by the sensor unit A as shown in FIG. 2B, and in the rear focus state, light reception is detected only by the sensor unit B as shown in FIG. 2C. The control unit 8 obtains an in-focus state as shown in FIG.
The correction lens 3 is driven to adjust the focal position of the laser and the image formation state on the surface to be scanned.

[0006]

However, in the case of the knife edge method, the laser beam to be scanned is imaged on the light receiving sensor 7 'in the form of a light spot, and the light spot is shielded in half by the edge E. In addition, it is necessary to accurately control the pulse emission. This complicates the control configuration.

Although not known, from the viewpoint of simplification of the configuration, the output from the light receiving sensor when laser scanning is performed without pulse light emission control, that is, the light amount peak value and the light receiving time are detected. There is also a method of determining a state in which is minimum as a good imaging state. However, in this case, the number of laser scanning and detection is increased,
There is a problem that it is necessary to perform control for searching for an optimal imaging state based on a large amount of detection information, and it takes time to adjust the focus.

Therefore, an object of the present invention is to obtain a laser focus position with a small number of detections even with a simple control configuration without pulse emission control, and to shorten the adjustment time of the image forming state. An object of the present invention is to provide an optical scanning device.

[0009]

In order to achieve the above object, an optical scanning apparatus according to the present invention comprises an optical scanning system for scanning a laser beam emitted from a light source onto an object to be scanned via an optical deflecting means and an imaging element. Detection means for detecting an imaging state near the focal position of the laser at a position equivalent to the surface to be scanned by the laser scanned by the optical scanning system; and a focus for adjusting the focal position of the detected laser. An optical scanning device, comprising: a position adjusting unit; and a control unit that controls the focal position adjusting unit based on the detection data output by the detecting unit. When the focus position is changed to a position before or after the focus position with respect to the means, two or more pieces of detection data having different defocus amounts before and after the focus position are fetched, and the focus position adjustment is performed based on the two or more pieces of detection data. It is characterized by controlling means.

The control means can change the focal position of the laser by driving the focus position adjusting means. Alternatively, the image forming state detecting means may include a plurality of light receiving units having different defocus positions with respect to the laser to be detected, so that the focal position of the laser can be changed. Further, a configuration for driving the focus position adjusting means and a configuration having a plurality of light receiving units may be used together.

The focus adjusting method according to the present invention further comprises detecting means for detecting an image forming state near the focal position of the laser at a position equivalent to the surface to be scanned, and determining the focal position of the laser with respect to the detecting means. Change to the front and back, at least two different defocus amounts in each of the front focus state and the rear focus state
Times, the change of the imaging state with respect to the change of the defocus amount in each focus state is approximated to a straight line based on the two detections, and the change is predicted from the intersection of two straight lines having different focus states. The focus position of the laser is adjusted to the in-focus position.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of the optical scanning device of the present embodiment. This optical scanning device includes a light source 1, a coupling lens 2, a correction lens 3, a rotating polygon mirror as light deflecting means 4, an imaging element 6, and a detection sensor 7 for detecting an imaging state of the laser L. And so on. The scanned object 9 is a photosensitive drum or the like supported at a predetermined position so that the laser L emitted from the scanning optical system forms an image on the surface. The imaging element 6 is composed of an fθ lens system and forms an image of the laser beam L on the scanned object 9 in the form of a light spot.
The moving speed of the light spot on the surface to be scanned in the main scanning direction is adjusted to be constant.

The focus position adjusting means for changing the focus position (also referred to as a waist position or a convergence point) of the laser L may be constituted by a stepping motor or the like for driving and controlling the moving stage 4 of the correction lens 3 as in the above-mentioned conventional example. it can. The correction lens 3 is placed on the moving stage 4.
A stepping motor or the like for driving the moving stage 4 is connected to the control unit 8, and the position of the correction lens 3 is controlled along the optical axis of the emitted laser of the light source. As a result, the focal position of the laser L transmitted through the correction lens 3 near the surface to be scanned is adjusted.

The means for detecting the image forming state of the laser L is constituted as follows. The detection sensor 7 is the scanning object 9
And a light receiving portion is provided at a position optically substantially equivalent to the scanned surface of the scanned body 9. That is, when the laser L is scanned, the light spot is arranged to pass over the light receiving portion of the detection sensor 7 at one end in the main scanning direction. Note that a photodiode or the like can be used as this type of detection sensor 7. The detection sensor 7 is connected to the control unit 8. The charge is accumulated in the light receiving unit by the incidence of the scanning laser L. The information on the stored charges is stored in the control unit 8.
And the imaging state of the laser L is determined. Although not shown, the control unit 8 includes a driving circuit unit that drives the position of the correction lens 3 via the moving stage 4, a CPU that can calculate the operation amount of the moving stage 4 based on the output of the detection sensor 7, and the like. And stores programs necessary for executing these arithmetic processes.

Next, control for adjusting the image forming state of the laser L by the optical scanning device having the above configuration will be described. FIG.
Indicates the output of the detection sensor 7 that has received light. The output of the detection sensor 7 when the light receiving portion is laser-scanned has a bell-shaped waveform with time on the horizontal axis. Let P be the peak light amount of this waveform, and let t be the time when the waveform is cut at a certain threshold s. In this case, the larger the peak light amount P and the shorter the time t, the better the imaging state. The time t is a detection time proportional to the light spot diameter in the main scanning direction. In the present embodiment, the imaging state is defined by the reciprocal (1 / P) of the peak light amount P or the time t, and the state in which the 1 / P or the time t is minimum is the minimum spot diameter on the surface to be scanned. This is an optimal imaging state.

In FIG. 3, the vertical axis represents the imaging state expressed by 1 / P and the like, and the horizontal axis represents the amount of movement of the correction lens 3. By repeating the process of detecting the laser L while changing the position of the correction lens 3 in the optical axis direction, that is, the focal position of the laser, and connecting a large number of detection results, a substantially “V” -shaped curve as shown in FIG. Can be

In the following, the position of the correction lens 3 once adjusted to the in-focus position by initializing the focus position or the like is set as a reference position (zero), and after the adjustment, the focal position of the laser is shifted due to some environmental change. The focus adjustment control of the present embodiment will be described with the “shifted” focus position as the focus position D.
For example, if the coupling lens 3 or the like is deformed due to a change in the temperature inside the apparatus, the focus position shifts from “0” to “D”. In addition, such focus adjustment
The focus adjustment control may be started by, for example, arranging a temperature detection sensor (not shown) near the coupling lens 3 and determining a change in temperature. Alternatively, the focus adjustment control may be periodically performed.

As shown in FIG. 3, at the focus position D,
1 / P or the time t takes a minimum value. In order to find the minimum value, for example, the correction lens 3 is sequentially driven to each defocus position and a large number of detections are required to determine the minimum peak light amount value. In addition, such trial-and-error adjustment is inefficient and takes time to adjust.

Therefore, in this embodiment, the changed focus position D is obtained by the following control calculation. For convenience of explanation, a defocus area that is in a front focus state across the in-focus position D is D ′, and a defocus area that is in a rear focus state is D ″.
And In each of the two focused states, detection is performed twice. Therefore, the number of times of detection is four times in total.

In the illustrated example, the correction lens 3 is at the previous adjustment position, that is, the reference position (zero). The correction lens 3 at the reference position is moved to the minus side, and is sequentially displaced to D1 and D2 within the defocus area D 'and having different defocus amounts. This movement from D1 to D2 is an area where the front focus state is increased, the spot diameter increases, and the time t (or 1 / P) increases in proportion to the spot diameter. The scanning and detection of the laser beam L are performed at the defocus positions D1 and D2.

Next, the correction lens 3 is driven in the opposite direction, that is, beyond the in-focus position D, to the back focus state. This defocus amount is performed with a relatively large drive amount that will surely exceed the focus position D. By this movement, the defocus position becomes D3. Even in the defocus area D ″ in the back focus state, detection is performed twice with different defocus amounts. In this example, laser detection is performed at two points D3 and D4. The drive amount from D3 to D4 is With approximately the same amount of driving from D1 to D2, the back focus state is increased, the spot diameter increases, and the time t increases in proportion to the spot diameter.
(Or 1 / P). The data of FIG. 4 is obtained by the above-described four detections.

As shown in FIG. 4, the defocus area D '
The points of the detection data (t or 1 / P) of the imaging state obtained at D1 and D2 in the (front focus state) are connected to each other to change the defocus amount in the defocus area D ′, that is, between D1 and D2. The imaging state change is approximated to a straight line L '.
Similarly, the detection data of D3 and D4 are connected to each other, and the change in the imaging state in the defocus area D ″ (back focus state) is approximated to a straight line L ″. Here, since the substantially V-shaped curve having the focus position D as the minimum value is substantially symmetrical about the focus position D, the absolute values of the change rates of the straight lines D ′ and D ″ before and after the curve are substantially equal. Therefore, as shown in Fig. 4, the minimum value defocus position, that is, the defocus position that gives the focus position D, is a straight line D 'and a straight line D ".
Required as an intersection with The in-focus position D is predicted by the calculation for finding the intersection, and the control unit 8 sends out an operation amount necessary for obtaining the in-focus position D, and drives the moving stage 4. In this example, since the defocus position before driving is the reference position (zero), if the correction lens 3 is driven to the plus side (from the previous reference position to the back focus state) by the movement amount D, the laser L It is possible to match the actual focal position to a surface (light receiving portion) equivalent to the surface to be scanned, and to obtain an optimal image forming state.

FIG. 5 shows another example of the configuration of the image forming state detecting means. In the above-described device, the detection sensor 7 includes one light receiving unit. However, the device in FIG. 5 uses a plurality of light receiving units 7a having different defocus positions with respect to the laser L to be detected.
To 7b. According to this configuration, it is possible to adjust the focal position from D1 to D4 without driving the moving stage 4. That is, the light receiving unit 7a and the light receiving unit 7b are arranged behind the position equivalent to the surface to be scanned in the optical axis direction (front focus area), and the light receiving unit 7c and the light receiving unit 7b are arranged.
On the other hand, d is disposed in front of the position equivalent to the surface to be scanned in the optical axis direction (back focus area). The area between the light receiving unit 7b and the light receiving unit 7c including the focus position of the laser L (the position equivalent to the surface to be scanned) is a range that covers the defocus due to the environmental change. Note that a configuration in which a light receiving unit is added at a position equivalent to the surface to be scanned (between the light receiving unit 7b and the light receiving unit 7c) may be used.

The defocus position is different between the light receiving section 7a and the light receiving section 7b in the front focus area along the optical axis direction of each of the lasers L detected by the light receiving section 7a. And the position of the light receiving section 7b is D2
Has become equivalent to. Also, the defocus position differs along the optical axis direction of each laser L similarly detected between the light receiving section 7c and the light receiving section 7d in the rear focus area, and the position of the light receiving section 7c corresponds to the above D3. However, the position of the light receiving section 7b corresponds to D2.
The outputs of the light receiving units 7a to 7d are taken into the control unit 8, and the detection data output by the light receiving units 7a, 7b, 7c, and 7d indicate the image forming state at the defocus positions D1, D2, D3, and D4, respectively. The focus position D is obtained by the above-described calculation.

According to the above configuration, there is no need for drive control for creating a defocus state between D1 and D4 via the focus position adjusting means, so that the control configuration is simplified and
It is excellent in that each output of D1 to D4 can be obtained by one laser scan.

[0026]

As described above, according to the present invention, when the focal position of the laser to be scanned and detected is changed to a position before and after the focus position with respect to the detection means, defocusing is performed before and after the focus position. Since two or more pieces of detection data having different amounts are fetched and the focus position adjusting means is controlled based on the two or more pieces of detection data, the focus position of the laser beam to be scanned with a simple control configuration and with a small number of detections ( (A waist position or a convergence point) can be obtained, and the time for adjusting the focal position can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an overall configuration of an optical scanning device according to an embodiment.

FIG. 2 is a diagram illustrating a detected image formation state of a laser.

FIG. 3 is a diagram illustrating a change in an imaging state with respect to a movement amount of a correction lens.

FIG. 4 is a diagram for finding a correction lens position that gives an optimal image forming state.

FIG. 5 is a plan view illustrating a configuration of an apparatus including a plurality of light receiving units.

FIG. 6 is a perspective view showing the overall configuration of a conventional optical scanning device.

FIG. 7 shows a knife edge method in a conventional apparatus.
3A shows a focused state, FIG. 3B shows a front focus state, and FIG.
FIG. 4 is an explanatory diagram showing a rear focus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light source 3, 4 Correction lens, moving stage (focal position adjusting means) 5 Light deflecting means 6 Imaging element 7 Detecting means 7a, 7b, 7c, 7d A plurality of light receiving parts with different defocus positions 8 Control part (Control means) D Focusing position with respect to the detection sensor L Laser to be scanned D ', D "Each defocus area L', L" Straight line

Claims (4)

[Claims] 1. An optical scanning system for scanning a laser beam emitted from a light source onto a scanning object via a light deflecting unit and an imaging element, and a scanning surface on which the laser beam scanned by the optical scanning system forms an image. Detecting means for detecting an imaging state near the focal position of the laser at an equivalent position; focal position adjusting means for adjusting the focal position of the detected laser; and a focal position based on the detection data output by the detecting means. Control means for controlling the adjustment means, wherein the control means, when the focal position of the laser is changed to before or after the focus position with respect to the detection means, before and after the focus position An optical scanning device, wherein two or more pieces of detection data each having a different defocus amount are taken in, and the focus position adjusting means is controlled based on the two or more pieces of detection data. 2. The optical scanning device according to claim 1, wherein said control means is capable of changing a focal position of said laser by driving said focal position adjusting means. 3. The image forming state detecting means includes a plurality of light receiving sections having different defocus positions with respect to a laser to be detected, so that a focal position of the laser can be changed. Item 2. The optical scanning device according to Item 1. 4. A detecting means for detecting an imaging state near a focal position of a laser at a position equivalent to a surface to be scanned, wherein the focal position of the laser is changed to a position before and after a focal position with respect to the detecting means. At least two detections with different defocus amounts are performed in each of the focus state and the back focus state,
The change of the imaging state with respect to the change of the defocus amount in each focus state is approximated to a straight line based on the number of times of detection, and the laser focus is moved to the focus position predicted from the intersection of the two straight lines having different focus states. A focus adjustment method for an optical scanning device, comprising adjusting a position.