JPH0735989B2 - Polygon mirror measuring instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention measures surface tilt, jitter, and surface entrance / exit during rotation of a polygon mirror used in a laser printer or the like.
The present invention relates to a polygon mirror measuring device.

(Prior Art) As evaluation characteristics of the deflection performance of conventional polygon mirrors, various types of evaluation are performed in consideration of the importance of variations in tilt angle of the reflecting surface (surface tilt) and uneven scanning (jitter). A method and an evaluation device are disclosed (for example, Japanese Patent Laid-Open No. 1-
221631, JP 64-63916, JP 64-28535
(See the official gazette).

Further, apart from the above-mentioned one, there has been proposed an apparatus for measuring the surface entrance / exit in consideration of the fact that the surface entrance / exit, that is, the fluctuation of the surface position affects the jitter measurement value.
(232226 publication).

Further, there has been proposed a device for simultaneously measuring these (application “optical deflector evaluation device” filed on September 13, 1990).

(Problems to be Solved by the Invention) Generally, a photodetector that detects a scanning light and generates a trigger signal generates a trigger signal by cutting a rising signal of the light amount at a constant voltage, and therefore, a rising slope of the light amount. The larger is, the more accurate the measurement can be. The rising slope is
If the spot size on the sensor is proportional to the scanning speed, and the spot size is considered to be the diffraction limit, the rising slope is proportional to the beam size on the reflecting mirror. In addition, there are cases where minute irregularities are present on the surface of the polygon mirror depending on the processing state. If the beam is small, the irregularities affect the surface. Therefore, the beam on the polygon mirror is preferably large. However, in recent years, the polygon mirror is generally made thin, and if the beam is enlarged on the reflecting surface, the polygon mirror is deflected up and down to reduce the amount of light. Therefore, if a surface tilt correction system of the type that has a focus on the polygon mirror only in the sub-scanning direction, the vertical direction becomes extremely small no matter how large the beam is,
Although this problem is solved, this optical system corrects the influence of the surface tilt, so that the surface tilt measurement cannot be performed using the same beam. On the other hand, for surface entering / exiting measurement, in order to eliminate the effect of unevenness on the surface, it is desirable to use an optical configuration in which the polygon mirror surface and the sensor are conjugated to form a point image on the polygon mirror. Since it has been corrected, it cannot be used for measuring troubles. Therefore, when using multiple light sources and arranging suitable optical systems respectively, the above problems do not occur, but if they are provided on the same plane, the beam for measuring tilting and entering / exiting the surface will be detected by the light for trigger generation. There is a problem that a trigger signal is generated when it is incident on the container and a great amount of labor is required to remove it by an electric circuit or software.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and the means will be described with reference to FIG. 1 corresponding to the embodiment. The incident light is from the first light source (1). Light (L1) polygon mirror (19)
The first focusing optical system (4)
(6) and the first cylindrical lens (5) having a focal point only in the sub-scanning direction on the polygon mirror surface (19a), and the first trigger sensor (8) from the first light source (1). Polygon mirror (1 so that reflected light (L2a) enters
With respect to 9), the second cylindrical lens () is provided obliquely downward and in a plane including the rotation axis and the incident light optical path so that the first trigger sensor (8) and the polygon mirror surface (19a) are conjugated. 7) is provided, and the second trigger sensor (10) is obliquely below the polygon mirror (19) and is the first trigger sensor so that the reflected light (L2b) from the first light source (1) enters. The third trigger sensor (10) is provided at a constant angle with respect to (8), and the third cylindrical lens (9) is provided so that the second trigger sensor (10) and the polygon mirror surface (19a) are conjugated. (12) so that the reflected light (L2c) from the first light source (1) is incident on the polygon mirror (19) obliquely downward and at a constant angle with respect to the first trigger sensor (8) in the scanning direction. And install it on the opposite side of the second trigger sensor (19). A fourth cylindrical lens (11) is provided so that the third trigger sensor (12) and the polygon mirror surface (19a) are conjugated, and the incident light (L3) from the second light source (2) is reflected by the polygon mirror (19). ) Obliquely from below, and the second condensing optical system (13) (14) is provided in front of the polygon mirror (19), and the second light source (2)
The reflected light (L2a) from the first light source (1) is obliquely above the polygon mirror (19) so that the incident light (L3) from the first trigger sensor (8) is incident on the polygon mirror (19). At the time point, a first optical position detector (15) for measuring the beam incident position in the direction perpendicular to the beam scanning direction is provided at the position where the reflected light (L4) from the second light source (2) is incident. , Incident light (L5) from the third light source (3) is horizontally incident on the polygon mirror (19), and the polygon mirror surface (19
a) A first condensing lens (16) having a focal point is provided in front of the polygon mirror (19), and reflected light (L2a) from the first light source (1) is the first trigger sensor (8). The second optical position detector (18) for measuring the beam incident position in the scanning direction is provided at the position where the reflected light (L6) from the third light source (3) is incident when A second condenser lens (17) is provided so that the optical position detector (18) and the polygon mirror surface (19a) are conjugated, and the second trigger sensor (10) and the third trigger sensor (12) Jitter is measured from the output of the first trigger sensor (8), and the surface tilt is measured from the output of the first optical position detector (15) at the time of the output of the first trigger sensor (8), and the output of the first trigger sensor (8) is measured. This is a polygon mirror measuring device for measuring the entrance and exit of the surface from the output of the second optical position detector (18).

(Operation) The operation of the present invention will be described below.

Incident light (L1) emitted from the first light source (1) passes through the first condensing optical systems (4) and (6), and the first cylindrical lens (5) allows the polygon mirror only in the sub-scanning direction. It is focused so that it has a focal point on the surface (19a). When the polygon mirror (19) rotates counterclockwise, the reflected light is first
After passing through the cylindrical lens (9), the light enters the second trigger sensor (10) (L2b). Next, the reflected light passes through the second cylindrical lens (7) and enters the first trigger sensor (8) as the polygon mirror (19) rotates (L2a). At this time, the incident light (L3) from the second light source (2) passes through the second condensing optical systems (13) and (14) and is reflected by the polygon mirror surface (19a) to reach the first light position. It is incident on the detector (15) (L4) and there is an output from the first trigger sensor (8).
The output of 5) is sent to the computer. Also at this time,
The incident light (L5) from the third light source (3) passes through the first condenser lens (16), is reflected by the polygon mirror surface (19a), passes through the second condenser lens (17), and The second optical position detector (1) when it is incident on the second optical position detector (18) (L6) and the output of the first trigger sensor (8) is present.
The output of 8) is sent to the computer. First and second
The outputs of the optical position detectors (15) and (18) are processed by a computer, and the amount of surface tilt and the amount of entering and leaving the surface are output. Next, the reflected light from the first light source (1) passes through the fourth cylindrical lens (11) as the polygon mirror (19) rotates, and enters the third trigger sensor (12) (L2c). . The outputs of the second trigger sensor (10) and the third trigger signal are input to the counter, and the jitter can be obtained by measuring the difference in the generation time of each output signal.

Next, the operation of the optical system will be described.

The first to collect the incident light (L1) emitted from the first light source (1)
The light collecting optical systems (4) and (6) collect light on the first, second, and third trigger sensors (8), (10), and (12). The first cylindrical lens (5) focuses the incident light (L1) emitted from the first light source (1) on the polygon mirror surface (19a) only in the sub-scanning direction. The second, third, and fourth cylindrical lenses (7), (9), and (11) have a refractive power only in the sub-scanning direction, and the first, second, and third trigger sensors (8) in the sub-scanning direction, respectively. (10) and (12) and the polygon mirror surface (19a) are located at a conjugate position. For example,
Even if the reflecting surface of the polygon mirror (19) is tilted in the sub-scanning direction, the polygon mirror surface (19a) and the sensor surface are conjugate with each other, so that there is no fluctuation in measurement. The second condensing optical system (13) (14) for condensing the incident light (L3) emitted from the second light source (2) is the first optical position detector via the polygon mirror surface (19a). (15) Focus the light on top. The first condenser lens (16) for condensing the incident light (L5) emitted from the third light source (3) has a polygon mirror surface (19).
a) Focus the light on top. The second condenser lens (17) is the third
The light (L6) reflected by the polygon mirror surface (19a) of the light source (3) is focused on the second light position detector (18), and is reflected by the polygon mirror surface (19a) and the second light. The position detector (18) is located at a conjugate position. for that reason,
For example, even if the angle of the reflected light (L6) changes due to the unevenness of the surface of the polygon mirror surface (19a), the position of focusing on the second optical position detector (18) does not change, so the polygon mirror surface (19a) ) Can only be measured.
Further, the incident light (L1) from the first light source (1) enters the polygon mirror (19) from diagonally below and is emitted obliquely above (L2a) (L2b) (L2c). Incident light (L3) emitted from the second light source (2) enters obliquely above the polygon mirror (19) and exits obliquely below (L4). Third light source (3)
The incident light (L5) emitted from the inside enters and exits at the same height as the polygon mirror (19) (L6). Therefore, the scanning light from the polygon mirror (19) of the light emitted from the first, second, and third light sources (1), (2), and (3) enters the respective target sensors and does not interfere with each other.

(Example) An example will be described with reference to FIG.

Incident light (L1) from the first light source (1) receives a first concave lens (4), a first converging optical system (4) (6) including a first convex lens (6), and a polygon mirror surface. After passing through the first cylindrical lens (5) that converges light only on the sub-scanning direction on (19a), the light is made incident obliquely above the polygon mirror (19) to move the first trigger sensor (8) to the first 1
So that the reflected light (L2a) from the light source (1) of
It is provided obliquely below the polygon mirror (19) and in a plane including the rotation axis and the incident beam optical path, and the second cylindrical is arranged so that the first trigger sensor (8) and the polygon mirror surface (19a) are conjugated. A lens (7) is provided, and the second trigger sensor (10) is obliquely below the polygon mirror (19) so that the reflected light (L2a) from the first light source (1) is incident on the second trigger sensor (10). It is provided at a constant angle in the scanning direction with respect to the trigger sensor (8), and a third cylindrical lens (9) is provided so that the second trigger sensor (10) and the polygon mirror surface (19a) are conjugate with each other. Reflected light (L2a) from the first light source (1) to the trigger sensor (12)
Is provided obliquely below the polygon mirror (19) so as to be incident on the polygon mirror (19) and at a constant angle in the scanning direction with respect to the first trigger sensor (8), on the opposite side of the second trigger sensor (10), A fourth cylindrical lens (11) is provided so that the third trigger sensor (12) and the polygon mirror surface (19a) are conjugated, and the incident light (L3) from the second light source (2) is reflected by the polygon mirror (19). ) Is incident obliquely from below, and a second condensing optical system (13) (14) including a second concave lens (13) and a second convex lens (14) in front of the polygon mirror (19).
Is provided diagonally above the polygon mirror (19) and at the time when the reflected light (L2a) from the first light source (1) enters the first trigger sensor (8), the second light source (2) The first light position detector (15) for measuring the beam incident position in the direction perpendicular to the scanning direction of the beam is provided at the position where the reflected light (L4) from the third light source (3) The incident light (L5) is horizontally incident on the polygon mirror (19), and a first condenser lens (16) having a focus on the polygon mirror surface (19a) is provided in front of the polygon mirror (19). (L6) from the third light source (3) when the reflected light (L2a) from the first light source (1) enters the first trigger sensor (8).
A second optical position detector (18) for measuring the beam incident position in the scanning direction is provided so that the beam is incident, and the second optical position detector (18) and the polygon mirror surface (19a) are conjugated. Is provided with a second condenser lens (17). In this embodiment, optical path changing mirrors (21), (22),
(23), (24), (25), (26), (27), (28),
(29), (30), (31) and (32) are used to achieve miniaturization. The outputs from the second trigger sensor (10) and the third trigger sensor (12) are input to the counter, and the jitter is measured from the time difference between the input signals. Also, the output of the first optical position detector (15) when the first trigger sensor (8) outputs and the output of the second optical position detector (18) when the first trigger sensor (8) outputs. Are sent to a computer and are arithmetically processed to be troubled and come and go.

The incident light (L1) emitted from the first light source (1) passes through the first condensing optical system (4) (6) including the first concave lens (4) and the first convex lens (6). The first cylindrical lens (5) focuses the light only on the polygon mirror surface (19a) in the sub-scanning direction. When the polygon mirror (19) rotates counterclockwise, the reflected light first passes through the third cylindrical lens (9) and enters the second trigger sensor (10) (L2b). Next, the reflected light passes through the second cylindrical lens (7) and enters the first trigger sensor (8) as the polygon mirror (19) rotates (L2a). At this time, the light from the second light source (2) passes through the second condensing optical system (13) (14) including the second concave lens (13) and the second convex lens (14), and the polygon mirror The surface of the first optical position detector (15) is reflected by the surface (19a) and is incident on the first optical position detector (15), and there is an output of the first trigger sensor (8). The output is sent to the computer. At this time, the light from the third light source (3) passes through the first condensing lens (16), is reflected by the polygon mirror surface (19a) and passes through the second condensing lens (17). The output of the second optical position detector (18) is sent to the computer when it is incident on the second optical position detector (18) and there is an output of the first trigger sensor (8). The outputs of the first and second optical position detectors (15) and (18) are arithmetically processed by a computer, and the amount of face tilt and the amount of face in and out are output respectively. Next, the light from the first light source (1) passes through the fourth cylindrical lens (11) and is incident on the third trigger sensor (12) as the polygon mirror (19) rotates. The outputs of the second trigger sensor (10) and the third trigger sensor (12) are input to the counter, and the jitter can be obtained by measuring the difference in the generation time of each output signal.

Next, the optical system will be described. A first condensing optical system including a first concave lens (4) and a first convex lens (6) for condensing light (L1) emitted from the first light source (1). (4) (6)
Collects light on the first, second and third trigger sensors (8), (10) and (12) after expanding the beam diameter. The first cylindrical lens (5) receives the incident light (L1) emitted from the first light source (1) only on the polygon mirror surface (19) in the sub-scanning direction.
a) Focus on top. Therefore, the beam diameter on the polygon mirror surface (19a) in the sub-scanning direction is extremely small, and even if the polygon mirror (19) is thin, the beam is not kicked in the sub-scanning direction. The second, third, and fourth cylindrical lenses (11) have a refractive power only in the sub-scanning direction, and the first, second, and third trigger sensors (12) and the polygon mirror surface (19a) in the sub-scanning direction, respectively. ) Is placed at a conjugate position. For example, even if the reflecting surface of the polygon mirror (19) is tilted in the sub-scanning direction, the polygon mirror surface (19a) and the sensor surface are conjugated, so there is no change in measurement due to this. The second condensing optical system (13) (14) including the second concave lens (13) and the second convex lens (14) that condense the light emitted from the second light source (2) After enlarging, the light is focused on the first optical position detector (15) via the polygon mirror surface (19a). A first condenser lens (16) for condensing the light emitted from the third light source (3)
Focuses the light on the polygon mirror surface (19a). Second
The condensing lens (17) focuses the light emitted from the third light source (3) and reflected by the polygon mirror (19) onto the second optical position detector (18), and the polygon mirror surface (19a ) And the second
The optical position detector (18) is located at a position conjugate with the optical position detector (18). Therefore, for example, even if the angle of the reflected light changes due to the unevenness of the surface of the polygon mirror surface (19a), the position where the light is focused on the sensor does not change, so only the position of the polygon mirror surface (19a) can be measured. . As described above, in the present invention, since the error is reduced by the optical system, highly accurate measurement can be performed for each measurement item. Furthermore, the window plate (2
0) to prevent wind from the polygon mirror (19) and to cover each optical path with a windbreak pipe (not shown in the figure) to eliminate errors due to changes in the refractive index of the air, making it possible to perform more accurate measurements. It will be possible. Further, the light from the first light source (1) enters the polygon mirror (19) from obliquely below and exits obliquely above. The light emitted from the second light source (2) enters obliquely above the polygon mirror (19) and exits obliquely below. The light emitted from the third light source (3) enters and exits at the same height as the polygon mirror (19). Therefore, the scanning light from the polygon mirror (19) of the light emitted from the first, second, and third light sources (3) respectively enters the target sensor and does not interfere with each other.

As described above, according to the present invention, it is possible to simultaneously measure the jitter, surface tilt, and surface entrance / exit, and since the surface tilt correction optical system is adopted for the jitter optical system, the error due to the surface tilt at the time of jitter measurement is removed. Even if the beam diameter is expanded in order to avoid the influence of surface irregularities, the beam diameter can be made extremely small in the sub-scanning direction, so that a polygon mirror having a small thickness can be used without any problem. In addition, since the optical path of each optical system is shifted in the vertical direction with respect to the scanning direction, each optical system does not interfere with each other and each optical system adopts an optical system suitable for each measurement, so highly accurate measurement is possible. it can. As described above, according to the present invention, a plurality of measurements regarding the polygon mirror can be simultaneously measured with high accuracy in a short time.

(Effects of the Invention) As described in detail above, the present invention has the following effects.

B) Jitter, trouble, and entrance / exit can be measured at the same time.

B) Since the jitter correction optical system is used for the jitter optics, errors due to surface tilt are eliminated during jitter measurement, and even if the beam diameter is widened to avoid the effects of surface irregularities, the sub-scanning direction Since the beam diameter can be made extremely small, a polygon mirror with a small thickness can be used without problems.

C) Since the optical paths of the optical systems are shifted in the scanning direction and in the vertical direction, the optical systems do not interfere with each other.

D) Since each optical system employs an optical system suitable for each measurement, it is possible to measure with high accuracy.

(E) Since the position of the polygon mirror surface can be accurately specified by the surface entering / exiting measurement system, stable measurement can be performed for each measurement.

As described above, the present invention has an advantage that a plurality of measurements regarding the polygon mirror can be simultaneously measured with high accuracy and stability in a short time.

[Brief description of drawings]

 Drawing is a perspective view of one example of the present invention. DESCRIPTION OF SYMBOLS 1 ... 1st light source 2 ... 2nd light source 3 ... 3rd light source 4 ... 1st concave lens 5 ... 1st cylindrical lens 6 ... 1st convex lens 7 ... 2nd cylindrical lens 8 ... 1st trigger Sensor 9 ... Third cylindrical lens 10 ... Second trigger sensor 11 ... Fourth cylindrical lens 12 ... Third trigger sensor 13 ... Second concave lens 14 ... Second convex lens 15 ... First optical position detector 16 ... 1st condensing lens 17 ... 2nd condensing lens 18 ... 2nd optical position detector 19 ... Polygon mirror 19a ... Polygon mirror surface 20 ... Window plates 21-32 ... Mirror L1 ... From 1st light source Incident light L2a, L2b, L2c ... Reflected light from the first light source L3 ... Incident light from the second light source L4 ... Reflected light from the second light source L5 ... Incident light from the third light source L6 ... Light reflected from light source 3

Claims (1)

[Claims] 1. An incident light (L1) from a first light source (1) is incident obliquely above a polygon mirror (19), and first condensing optical systems (4) (6) and a polygon mirror surface. (19a)
A first cylindrical lens (5) having a focal point only in the sub-scanning direction is provided on the upper side, and a first trigger sensor (8) is attached to the first
The first trigger sensor (8) is provided obliquely downward with respect to the polygon mirror (19) so that the reflected light (L2a) from the light source (1) is incident on the plane including the rotation axis and the incident light optical path.
And the polygon mirror surface (19a) are conjugated to each other.
The cylindrical lens (7) is provided, and the second trigger sensor (10) is placed obliquely below the polygon mirror (19) so that the reflected light (L2b) from the first light source (1) enters. The first trigger sensor (8) is provided at a constant angle in the scanning direction, and the third trigger lens (10) and the polygon mirror surface (19a) are provided with a third cylindrical lens (9) so as to be conjugate with each other. 3 trigger sensors (12)
So that the reflected light (L2c) from the first light source (1) is incident on the polygon mirror (19) obliquely downward and at a constant angle with respect to the first trigger sensor (8) in the scanning direction. , Provided on the opposite side of the second trigger sensor (10), and provided with a fourth cylindrical lens (11) so that the third trigger sensor (12) and the polygon mirror surface (19a) are conjugated.
The incident light (L3) from the second light source (2) is made incident obliquely below the polygon mirror (19), and the polygon mirror (19)
The second condensing optical system (13) (14) is provided in front of the polygon mirror (19), obliquely above the polygon mirror (19) and at the first light source (1).
When the reflected light (L2a) from the second light source (2) is incident on the first trigger sensor (8), the reflected light (L2a) from the second light source (2)
At the position where 4) is incident, a first optical position detector (15) for measuring the beam incident position in the direction perpendicular to the scanning direction of the reflected light (L4) is provided, and the first light position detector (15) from the third light source (3) is provided. Incident light (L
5) is made to enter the polygon mirror (19) horizontally, and the first condensing lens (1
6) is provided in front of the polygon mirror (19), and when the reflected light (L2a) from the first light source (1) enters the first trigger sensor (8), it is emitted from the third light source (3). A second optical position detector (18) for measuring the beam incident position in the scanning direction is provided at the position where the beam is incident, and the second optical position detector (18) and the polygon mirror surface (19a) are conjugated. As described above, the second condenser lens (17) is provided, the jitter is measured from the outputs of the second trigger sensor (10) and the third trigger sensor (12), and the output of the first trigger sensor (8) is measured. of time,
A feature is that the surface tilt is measured from the output of the first optical position detector (15), and the surface entrance / exit is measured from the output of the second optical position detector (18) at the time of the output of the first trigger sensor (8). And a polygon mirror measuring instrument.