JP3313985B2 - Laser beam measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam measuring apparatus for measuring dynamic laser beam performance in a laser beam printer in a rotating polygon mirror for scanning a laser beam.

[0002]

2. Description of the Related Art Conventionally, a laser beam printer is configured as shown in FIG. 6 to form a two-dimensional image.
A laser beam whose intensity is temporally changed in accordance with the image density is emitted from the fixedly arranged laser emitting unit 1,
The light is guided to a rotary polygon mirror 4 through an optical system including a collimator lens 2 and a cylindrical lens 3. This laser beam is subjected to one-dimensional main scanning by a rotating polygon mirror 4 which rotates at high speed in the direction of arrow A about a rotation axis O, and a scanning lens 5 which is an fθ lens causes a surface of a photosensitive drum 6 which is a cylindrical photosensitive member to be scanned. A line image is formed in the direction of the generatrix B.

When the photosensitive drum 6 rotates about the rotation axis X, a one-dimensional sub-scan perpendicular to the main scan is performed, and a two-dimensional image is printed out. Therefore,
The image forming state of the laser beam on the surface of the photosensitive drum 6 and the linearity of the main scanning affect the performance of the printer. Conventionally, in the stationary state where the rotation of the rotary polygon mirror 4 is stopped, the photosensitive drum 6
It detects the imaging state of the laser beam on the surface.

[0004]

However, in the above-mentioned conventional example, since the laser beam is not measured while the rotary polygon mirror 4 is rotating in an actual operating state, the rotary polygon mirror 4 rotates. Laser in a state that includes the influence of the deformation of the reflecting surface due to the mechanical force generated by the rotation and the heat conduction from the rotary driving unit, and the influence of the disturbance of the surrounding air generated by the rotation of the rotary polygon mirror 4. There is a problem that the imaging performance of the beam cannot be understood.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a laser beam measuring device for measuring the imaging performance of a laser beam in a rotating state of a rotary polygon mirror.

[0006]

According to the present invention, there is provided a laser beam measuring apparatus comprising: a laser emitting section for turning on and off a pulse in synchronization with the rotation scanning of a rotary polygon mirror; A driving unit that moves an optical system that determines the imaging performance described above, and a measurement that is arranged at a position corresponding to the imaging on the surface of the photosensitive drum and measures the imaging state of the laser beam along a direction corresponding to the generatrix of the photosensitive drum. Unit, having a scanning timing detection unit for detecting the scanning timing of the laser beam scanning by the rotating polygon mirror, the optical system position and the measurement position related to the image of the laser beam while rotating the rotating polygon mirror. In this case, the imaging state of the laser beam is measured at each position by the measurement unit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 shows a plan view of the embodiment. A collimator lens 11 that moves in the optical axis direction to change the focus position in the main scanning direction is provided on an optical path in front of a laser beam emitting unit 10 that emits a laser beam. A cylindrical lens 12 that moves in the optical axis direction to change the focus position in the sub-scanning direction, and a rotary polygon mirror 13 that rotates at a high speed in the direction of arrow T are sequentially arranged, and are arranged on the optical path in the reflection direction of the rotary polygon mirror 13. A scanning lens 14 having a focal point at a position P corresponding to a photosensitive drum, and a laser beam measuring unit 15 having a two-dimensional sensor or the like at an image forming position by the scanning lens 14. The laser beam measuring unit 15 has a moving mechanism 16 that can move to an arbitrary position in the main scanning direction, and a laser beam scanning timing detecting unit 17 having a photoelectric sensor is provided at an end position of the scanning laser beam. .

The laser beam from the laser beam emitting unit 10 passes through a collimator lens 11 and a cylindrical lens 12, is reflected by a rotary polygon mirror 13, is scanned by a scanning lens 14, and focuses on a photosensitive drum equivalent position P to form a straight line. An image is formed. The laser beam measuring unit 15 measures the intensity distribution of the laser beam at this image position,
The scanning timing detecting unit 17 detects the scanning timing of the laser beam by the rotating polygon mirror 13 and generates the timing for turning on the laser beam emitting unit 10 in a pulse and the measuring timing of the laser beam measuring unit 15.

FIG. 2 is a flowchart of the measurement operation. In the measurement of the laser beam in the main scanning direction, first, the rotating polygon mirror 13 is rotated in step S1, and the cylindrical lens 12 is moved to the in-focus position in the sub scanning direction in step S2. Keep moving. Next, in step S3, the measuring unit 15 is moved to the initial position of the main scanning position by the moving mechanism 16, and in step S4, the collimator lens 11 that changes the focus position in the main scanning direction at the moving position in the main scanning direction is moved to the initial position. Go to

In steps S5, S6, and S7, while moving the collimator lens 11 within the movement range including the in-focus position, the measuring unit 15 obtains the intensity distribution of the laser beam for each position of the collimator lens 11, and obtains the laser beam intensity distribution. The beam diameter in the main scanning direction is measured, and the position where the beam diameter becomes smallest is set as the focus position. In this manner, a change in the beam diameter with respect to the movement of the position of the collimator lens 11 can be measured. However, since this is a measurement at one point in the main scanning direction, the measuring unit 15 is appropriately moved by the moving mechanism 16 in steps S8 and S9. While the same operation is being performed, the change of the focus position in the main scanning direction is measured.

Since the measurement of the laser beam is performed while the rotary polygon mirror 13 is being rotated, a period from when the laser beam is detected by the scanning timing detecting unit 17 to when the laser beam enters the visual field of the two-dimensional sensor of the laser beam measuring unit 15 is measured. In addition, the laser beam can be measured in a nearly stationary state by pulsing the laser beam emitting unit 10 for a sufficiently short time during which the laser beam moves during scanning by the rotating polygon mirror 13.

The measurement of the laser beam is performed in a state where the intensity of the laser beam received by the laser beam measuring unit 15 is distributed in the main scanning direction and the sub-scanning direction, and when the intensity distribution shows the steepest distribution. As the focus position,
It is measured by how far it is from or has spread.

FIG. 3 is a diagram showing contour lines of the intensity distribution of the laser beam picked up by the two-dimensional sensor of the laser beam measuring unit 15 at the in-focus position. FIG. (b) is the intensity distribution when it is out of focus. FIG. 4 shows a line L of the laser beam shown in FIG.
4 (a) and 4 (b) respectively show a one-dimensional cross-section along the line, and the distribution when the vertical axis indicates intensity and the horizontal axis indicates position.
(a) and (b) are supported.

The beam diameter is defined as a distance from the position C1 to the position C2 when the threshold value H is set to a predetermined ratio to the peak value of the intensity in FIG. 4A, for example, 1 / e ² ≒ 0.35. Measure. On the other hand, FIG. 4B shows that the beam diameter D when deviated from the in-focus position is shifted from the position D1 to the position D2.
, And the beam diameter D is larger than the beam diameter C.

Further, as shown in FIG. 5, the focusing range can be measured by obtaining the beam diameter at each position while shifting the collimator lens 11. If the vertical axis indicates the beam diameter and the horizontal axis indicates the position of the collimator lens 11, the change in the beam diameter at this time will be like distributions E and F. At this time, a predetermined threshold value H is set for the beam diameter as the focusing range, and the position of the collimator lens 11 having a beam diameter equal to or smaller than the threshold value H is determined as the focusing range. That is, in the distribution E, the range from the position E1 to the position E2 of the collimator lens 11 is set as the focusing range.
Is the focusing range.

The effect of the rotation of the rotary polygon mirror 13 is determined by adjusting the rotation angle of the rotary polygon mirror 13 to a position where the laser beam enters the laser beam measuring unit 15 with the rotary polygon mirror 13 stationary. For measuring the image performance, and measuring the image performance when the rotating polygon mirror 13 is rotated,
The measurement is performed based on the in-focus position, the in-focus range, and how much the laser beam spreads. For example, in FIG. 5, a distribution curve E represents a beam diameter change curve measured when the rotary polygon mirror 13 is stationary, and a distribution curve F represents a beam diameter change curve measured when the rotary polygon mirror 13 is rotating. It can be seen that the focusing range is shifted between the two.

The laser beam measuring unit 15 is moved to a moving mechanism 16
Instead of moving the laser beam, a plurality of laser beam measuring units 15 may be arranged at appropriate positions in the moving direction. When measuring while rotating the rotary polygon mirror 13, instead of turning on the laser beam in pulses, high-speed A two-dimensional sensor having a shutter function may be used. Furthermore, the rotating polygon mirror 13
It is also possible to measure the characteristics while arbitrarily changing the number of rotations.

[0018]

As described above, the laser beam measuring apparatus according to the present invention dynamically measures the intensity distribution of the laser beam while the rotating polygon mirror for scanning the laser beam is rotating. It is possible to measure the effect of the rotation of the rotating polygon mirror on the scanning characteristics of the laser beam.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a flowchart of a measurement operation.

FIG. 3 is a contour diagram of an intensity distribution of a laser beam.

FIG. 4 is a graph showing an intensity distribution of a laser beam.

FIG. 5 is a graph showing a focusing range according to a beam diameter;

FIG. 6 is a configuration diagram of a conventional laser beam printer.

[Explanation of symbols]

 Reference Signs List 10 laser beam emitting part 11 collimator lens 12 cylindrical lens 13 rotating polygon mirror 14 scanning lens 15 laser beam measuring part 16 moving mechanism 17 scanning timing detecting part

Claims (3)

(57) [Claims] 1. A laser emitting unit which emits a pulse in synchronization with the rotation scanning of a rotary polygon mirror, a driving unit which moves an optical system for determining an imaging performance on a cylindrical photosensitive drum surface, A measuring unit arranged at a position corresponding to the image formation on the surface and measuring the image forming state of the laser beam along a direction corresponding to the generatrix of the photosensitive drum; and a scanning timing detection for detecting a scanning timing of the laser beam scanned by the rotary polygon mirror. And changing the optical system position and the measurement position related to the imaging of the laser beam while rotating the rotating polygon mirror, and measuring the imaging state of the laser beam by the measurement unit at each position. A laser beam measuring device characterized by the above-mentioned. 2. The laser beam measuring apparatus according to claim 1, wherein the measuring section moves in a direction corresponding to a generatrix of the photosensitive drum. 3. The method according to claim 1, wherein an effect of the rotation of the rotary polygon mirror is measured by comparing an image forming state of the laser beam when the rotary polygon mirror rotates and an image forming state at a standstill. Laser beam measuring device.