JPH06294904A - Helical mirror and laser scanner using the same - Google Patents

Abstract

PURPOSE:To make a scan with the light reflected on the reflecting surface by forming the reflecting surface spirally and rotating the reflecting surface around the spiral axis thereby moving the incidence position of light, which is made incident on a reflecting surface in parallel to a spiral axis, in the direction of the spiral axis. CONSTITUTION:The helical mirror 1 has the spiral reflecting surface 4 and the spiral axis is aligned with the column axis of a body 2. The angle between the reflecting surface 4 and the spiral axis of the helical mirror 1 is set to 45 deg.. When the helical mirror 1 is used for the laser scanner, the helical mirror 1 is rotated on the spiral axis at an equal angular speed and the laser light which travels in parallel to the spiral axis is made incident on the reflecting surface 4. The point where the laser light is made incident on the reflecting surface 4 is placed in equal-speed motion in parallel to the spiral axis according to the equal-angular-velocity motion of the helical mirror 1. When the helical mirror 1 rotates clockwise, the point where the laser light is made incident on the reflecting surface 4 moves up once the point where the laser light is made incident on the reflecting surface 4 reaches the lower end of the helical mirror 1.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a laser printer,
The present invention relates to a helical mirror used in bar code readers, copying machines, etc., and a laser scanner using the helical mirror.

[0002]

2. Description of the Related Art In a laser printer, a laser scanner using a polygon mirror (polyhedral mirror) is used for scanning a laser beam on a photosensitive drum at a high speed.

If the polygon mirror has a division angle error,
The exposure width (that is, the scanning width) on the photosensitive drum changes. For this reason, a photo sensor is provided near the photoconductor drum to detect the laser light, and by this, the writing position of the image signal on the photoconductor drum is controlled so that the exposure width is apparently constant. There is.

Further, since the polygon mirror rotates at a constant angular velocity, the scanning speed of the laser light differs depending on the position on the photosensitive drum. For this reason, an f.theta. Lens is provided between the polygon mirror and the photosensitive drum, and the scanning speed of the laser light is corrected so as to be constant on the photosensitive drum.

[0005]

However, in the above-mentioned conventional structure, a photosensor is required to keep the exposure width constant, and since the scanning speed of the laser light is kept constant on the photosensitive drum, f.theta. Since the lens is required, the number of parts is increased and it is difficult to downsize the laser printer.

[0006]

In order to solve the above-mentioned problems, the helical mirror according to the invention of claim 1 forms a reflecting surface in a spiral shape, and rotates the reflecting surface around a spiral axis. The incident position of the light incident on the reflecting surface parallel to the spiral axis is moved in the spiral axis direction.

The helical mirror according to the invention of claim 2 is
In order to solve the above problems, the helical mirror according to claim 1 is characterized in that the angle formed by the spiral axis and the reflecting surface is set to 45 degrees.

In order to solve the above-mentioned problems, the laser scanner according to the invention of claim 3 forms a reflecting surface in a spiral shape, and rotates the reflecting surface around the spiral axis,
A helical mirror in which the incident position of the laser light incident on the reflecting surface parallel to the spiral axis moves in the spiral axis direction,
Rotation driving means for rotating the helical mirror around the spiral axis is provided, and the laser light incident parallel to the spiral axis is reflected by the reflecting surface of the rotating helical mirror, and scanning is performed by the reflected laser light. Is characterized by.

In order to solve the above-mentioned problems, a laser scanner according to a fourth aspect of the present invention is the laser scanner of the third aspect, wherein the angle formed by the helical axis of the helical mirror and the reflecting surface is set to 45 degrees. The helical mirror is characterized by being driven to rotate at a constant angular velocity.

In order to solve the above-mentioned problems, a laser scanner according to a fifth aspect of the present invention is the laser scanner of the fourth aspect, wherein the laser light reflected by the reflecting surface of the helical mirror is refracted only in the spiral axis direction. It is characterized in that a projection lens is provided.

In order to solve the above problems, a laser scanner according to a sixth aspect of the present invention is the laser scanner of the fourth aspect, further comprising a rotation angle detecting means for detecting the rotation angle of the helical mirror. The on / off control of the laser light is performed based on the rotation angle.

[0012]

According to the structure of claim 1, by forming the reflecting surface in a spiral shape and rotating the reflecting surface around the spiral axis,
Since the incident position of the light incident on the reflecting surface parallel to the spiral axis is moved in the spiral axis direction, scanning can be performed by the light reflected on the reflecting surface. Moreover, since the spiral reflecting surface is used, in principle, the correction of the division angle error required in the polygon mirror becomes unnecessary.

According to the structure of claim 2, the angle formed by the spiral axis and the reflecting surface is set to 45 degrees. Therefore, in addition to the function of claim 1, the laser beam is made to enter in parallel to the spiral axis. Light can be reflected in a direction orthogonal to the spiral axis. Moreover, by rotating the helical mirror at a constant angular velocity, it becomes possible to scan the laser beam at a constant velocity in the spiral axis direction.

According to the third aspect of the invention, a compact and simple laser scanner can be realized by using the helical mirror of the first aspect.

According to the structure of claim 4, by using the helical mirror of claim 2, it is possible to realize a laser scanner having a small size and a simple structure. Moreover, since the rotation driving means for rotating the helical mirror at a constant angular velocity is provided, it is possible to scan the laser beam in the spiral axis direction at a constant velocity. For this reason, when this laser scanner is used for a laser printer, for example, the f.theta. Lens for speed correction required in the polygon mirror becomes unnecessary.

According to the structure of claim 5, in addition to the operation of claim 4, since the projection lens for refracting the laser light reflected by the reflection surface of the helical mirror only in the spiral axis direction is provided, the scanning width of the laser light is provided. Can be extended. This makes it possible to obtain a desired scanning width with a small helical mirror.

According to the structure of claim 6, in addition to the operation of claim 4, a rotation angle detecting means for detecting the rotation angle of the helical mirror is provided, and the on / off control of the laser light is performed based on the rotation angle. The timing when modulating the laser light according to the image information can be easily taken.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.
The explanation is based on the following.

As shown in FIG. 1, the helical mirror 1 of this embodiment has a structure in which a protrusion 3 having a rectangular cross section is spirally formed on the side surface of a cylindrical body 2, The reflecting surface 4 is formed along one surface (one surface on the left side in the figure). That is, the helical mirror 1 has the spiral reflecting surface 4. The spiral shaft and body 2
The cylindrical axes of are in agreement.

The angle formed by the reflecting surface 4 and the spiral axis of the helical mirror 1 is set to about 45 degrees as shown in FIG. 2 (a developed view of the helical mirror 1).

When the above-mentioned helical mirror 1 is used in a laser scanner, as shown in FIG. 3, the helical mirror 1 is rotated around the spiral axis at an equal angular velocity, and a laser beam 5 traveling parallel to the spiral axis is reflected on the reflecting surface 4. Incident on.

The point at which the laser light 5 enters the reflecting surface 4 is
Along with the uniform angular velocity motion of the helical mirror 1, the constant velocity motion is performed in parallel with the spiral axis. When the helical mirror 1 rotates in the clockwise direction (CW direction in the figure), the laser light 5 reflects on the reflecting surface 4.
As shown in FIGS. 7A to 7C, the point of incidence on the point makes a uniform motion from top to bottom. When the point where the laser light 5 enters the reflecting surface 4 reaches the lower end of the helical mirror 1, the point where the laser light 5 enters the reflecting surface 4 jumps upward.
Hereinafter, this operation is repeated.

In the helical mirror 1 of this embodiment, the angle between the reflecting surface 4 and the spiral axis of the helical mirror 1 is about 45.
Since the laser beam 5 is set in degrees, the laser beam 5 is reflected by the reflecting surface 4 in the direction perpendicular to the surface. Therefore, the helical mirror 1 of the present embodiment
In the laser scanner using, the laser light 5 can be reflected in the direction perpendicular to the spiral axis of the helical mirror 1, and the laser light 5 can be moved in the spiral axis direction at a constant speed.

The scanning width (l) of the laser beam 5 is l = πD, where D is the diameter of the helical mirror 1 (see FIG. 2).

As an application example of the above laser scanner, a laser printer is cited, and the construction of its optical scanning system is shown in FIG.

The optical scanning system of a laser printer includes a semiconductor laser 11, a collimator lens 12 for converting a laser beam 5 from the semiconductor laser 11 into a parallel beam, a helical mirror 1, and a helical mirror 1 around its spiral axis. DC (direct current) motor that rotates at a constant angular velocity 1
3 and a rotary encoder 1 that is directly connected to the rotation shaft of the DC motor 13 and detects the rotation angle of the DC motor 13.
4 (rotation angle detecting means).

Further, the optical scanning system includes a projection lens 15 for refracting the laser light 5 reflected by the helical mirror 1 only in the axial direction of the photosensitive drum 17 (X-axis direction in the figure), and the laser light from the projection lens 15. A cylindrical lens 16 is provided for refracting 5 only in a direction orthogonal to the axial direction of the photoconductor drum 17 (Z-axis direction in the drawing).

The projection lens 15 is arranged so that the laser beam 5 reflected by the helical mirror 1 and the central axis of the projection lens 15 are parallel to each other. Further, the collimator lens 12 is arranged so that the parallel beam is incident on the reflecting surface 4 of the helical mirror 1 in parallel with the spiral axis of the helical mirror 1.

In the above laser printer configuration, the laser light 5 from the semiconductor laser 11 is incident on the collimator lens 12 and is converted into a parallel beam.
The light enters the reflecting surface 4 of the helical mirror 1. The laser light 5 reflected by the helical mirror 1 enters the projection lens 15, is refracted in the X-axis direction, and enters the cylindrical lens 16. The laser light 5 incident on the cylindrical lens 16 is refracted in the Z-axis direction and projected onto the photoconductor drum 17.

Laser light 5 reflected by the helical mirror 1
Is incident parallel to the optical axis of the projection lens 15, so that it always passes through the focal point (f in the figure) of the projection lens 15. Therefore,
If the positional relationship between the projection lens 15 and the photosensitive drum 17 is appropriately determined according to the focus, the width L in the main scanning direction can be set freely. In addition, the cylindrical lens 16
Thus, the surface tilt error of the reflecting surface 4 of the helical mirror 1 can be corrected.

In the laser printer of this embodiment, the DC
The motor 13 rotationally drives the helical mirror 1 having the reflecting surface 4 of 45 degrees at a constant angular velocity. Therefore, the laser beam 5 can scan the photosensitive drum 17 in the axial direction at a constant speed.

As a result, the f.theta. Lens necessary for keeping the scanning speed constant in the polygon mirror is not necessary in principle in the laser printer of this embodiment. Also,
The photosensor and the like required for correcting the division angle error of the polygon mirror are also unnecessary in the laser printer of this embodiment using the helical mirror 1.

Further, in the laser printer of this embodiment, the rotation angle of the DC motor 13 is detected by the rotary encoder 14 directly connected to the axis. Therefore, the laser beam 5 can be turned on / off at the scanning position proportional to the rotation angle of the helical mirror 1 only by controlling the on / off of the semiconductor laser 11 in synchronization with the detection signal of the rotary encoder 14. . Therefore, the timing control when modulating the semiconductor laser 11 according to the image information becomes extremely simple.

Further, in the laser printer of this embodiment, the projection lens 15 for refracting the laser beam 5 only in the X-axis direction is provided with the helical mirror 1 and the cylindrical lens 16.
And the scanning width of the laser beam 5 on the photosensitive drum 17 can be increased. In other words, the size of the helical mirror 1 required to obtain a desired scanning width on the photoconductor drum 17 can be reduced.

For example, when forming an image of A3 size, the scanning width on the photosensitive drum 17 is 297 mm, so if the projection lens 15 is not used, the length is 2 mm.
A large helical mirror 1 having a diameter of 97 mm and a diameter of 95 mm (see the above formula) is required. On the other hand, when the projection lens 15 that enlarges the scanning width by n times is used, the helical mirror 1
Can be reduced to 1 / n.

Although the projection lens 15 expands the spot diameter of the laser beam 5 on the photosensitive drum 17,
It can be easily adjusted by adding a lens system.

The second embodiment of the present invention will be described below with reference to FIGS. 5 to 7. For convenience of explanation, members having the same functions as those of the members shown in the drawings of the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the helical mirror 1 of this embodiment, as shown in FIG. 5 (exploded view of the helical mirror 1), the angle formed by the reflecting surface 4 and the helical axis of the helical mirror 1 is not constant but continuously changes. It is different from the above-mentioned embodiment in that.
That is, in the helical mirror 1 of this embodiment, the twist angle is not constant.

X with the helical axis of the helical mirror 1 as the x axis
In the −y coordinate system, it is assumed that the reflecting surface 4 is formed along a curve, y = f (x).

The reflection at each point on the reflecting surface 4 is equivalent to the reflection by the plane having the same inclination as that of the reflecting surface 4 at that point. In the present embodiment, consider a reflecting surface 4 in which the inclination of the reflecting surface 4 satisfies the following equation.

Dy / dx = tan θ tan2θ = k / x where k is a constant. Rewriting these equations gives dy / dx = −x / k + (x ² + k ² ) ^1/2 / k. Solving the above differential equation under the initial condition of f (0) = 0 f ′ (0) = 1, f (x) = − x / k + {x (x ² + k ² ) ^1/2 / 2 + k
² log | x + (x ² + k ² ) ^1/2 |}.

K in f (x) is defined, for example, by the following equation.

K = lA / (L-l)> 0 where l is the axial length of the helical mirror 1, 2L is the axial length of the photosensitive drum 17, and A is the axial length of the helical mirror 1. This is the distance between the surfaces of the photosensitive drums 17.

In the case of the helical mirror 1 in which the reflecting surface 4 is formed along this f (x), as shown in FIG. 6, the laser light 5 is directed onto the photosensitive drum 17 without using the projection lens 15. You can scan from to the edge.

That is, according to the helical mirror 1 of this embodiment, the photoconductor drum 1 can be used without using the projection lens 15.
The scanning width of the laser beam 5 on 7 can be enlarged. In other words, the size of the helical mirror 1 required to obtain a desired scanning width on the photoconductor drum 17 can be reduced, and the projection lens 15 is unnecessary.

When the helical mirror 1 is rotationally driven at a constant angular velocity, as shown in FIG. 7, the photosensitive drum 1
The scanning speed of the laser beam 5 on 7 is not constant. Therefore, speed correction is required to keep the scanning speed constant.

In the above embodiments, the cylindrical body 2 is used for the helical mirror 1. However, if the cylindrical body 2 is used, the weight of the helical mirror 1 can be reduced.

A laser printer has been given as an application example of a laser scanner using the helical mirror 1, but the present invention is not limited to this, and the present invention can be widely applied to copiers, bar code readers and the like.

The helical mirror 1 according to the invention of claim 1
Forms the reflecting surface 4 in a spiral shape and rotates the reflecting surface 4 around the spiral axis, so that the incident position of the laser light 5 incident on the reflecting surface 4 parallel to the spiral axis moves in the spiral axis direction. Since it did so, it becomes possible to scan with the laser beam 5 reflected by the reflecting surface 4. Moreover, since the spiral reflecting surface 4 is used, it is theoretically unnecessary to correct the division angle error required in the polygon mirror.

The helical mirror 1 according to the invention of claim 2
Is the helical mirror 1 of claim 1, wherein the angle formed by the spiral axis and the reflecting surface 4 is set to 45 degrees. Therefore, in addition to the effect of the first aspect, the laser beam 5 is made parallel to the spiral axis. By making it incident, the laser light 5 can be reflected in a direction orthogonal to the spiral axis. Moreover, by rotating the helical mirror 1 at a constant angular velocity, it becomes possible to scan the laser beam 5 in the spiral axis direction at a constant velocity.

In the laser scanner according to the invention of claim 3, the reflecting surface 4 is spirally formed, and the reflecting surface 4 is rotated about the spiral axis so that the reflecting surface 4 is incident on the reflecting surface 4 in parallel with the spiral axis. A helical mirror 1 in which the incident position of the light 5 moves in the spiral axis direction, and a rotary encoder 1 for rotationally driving the helical mirror 1 around the spiral axis.
4 is provided, the laser light 5 incident parallel to the spiral axis is reflected by the reflecting surface 4 of the rotating helical mirror 1, and scanning is performed by the reflected laser light 5. Therefore, the helical mirror 1 according to claim 1 is provided. By using it, a laser scanner with a small size and a simple structure can be realized.

A laser scanner according to a fourth aspect of the present invention is the laser scanner according to the third aspect, wherein an angle formed by the helical axis of the helical mirror 1 and the reflecting surface 4 is set to 45 degrees. Since it is rotationally driven at a constant angular velocity, a small and simple laser scanner can be realized by using the helical mirror 1 of the second aspect. Moreover, since the rotary encoder 14 that rotationally drives the helical mirror 1 at a constant angular velocity is provided, the laser beam 5 can be scanned at a constant velocity in the spiral axis direction. Therefore, if this laser scanner is used in a laser printer, for example, the f.theta. Lens for speed correction required in the conventional polygon mirror becomes unnecessary.

A laser scanner according to a fifth aspect of the present invention is the laser scanner of the fourth aspect, further comprising a projection lens 15 for refracting the laser light 5 reflected by the reflection surface 4 of the helical mirror 1 only in the spiral axis direction. Therefore, in addition to the effect of the fourth aspect, the scanning width of the laser light 5 can be widened. This makes it possible to obtain a desired scanning width with the small helical mirror 1.

A laser scanner according to a sixth aspect of the present invention is the laser scanner according to the fourth aspect, further comprising rotation angle detecting means for detecting the rotation angle of the helical mirror 1, and the laser beam is detected based on the rotation angle. Since the ON / OFF control of 5 is performed, in addition to the effect of the fourth aspect, it is possible to easily set the timing when modulating the laser light 5 according to the image information.

[0055]

As described above, the helical mirror according to the first aspect of the present invention forms the reflecting surface in a spiral shape and rotates the reflecting surface around the spiral axis so that the reflecting surface is parallel to the spiral axis. Since the incident position of the light incident on is moved in the spiral axis direction, scanning can be performed by the light reflected by the reflecting surface. Moreover, the correction of the division angle error required in the polygon mirror is theoretically unnecessary.

The helical mirror according to the invention of claim 2 is
As described above, in the helical mirror of claim 1, since the angle formed by the spiral axis and the reflecting surface is set to 45 degrees, in addition to the effect of claim 1, the laser light is incident parallel to the spiral axis. By doing so, the laser light can be reflected in the direction orthogonal to the spiral axis. Moreover, by rotating the helical mirror at a constant angular velocity, it is possible to scan the laser beam in the spiral axis direction at a constant velocity.

As described above, the laser scanner according to the invention of claim 3 forms the reflecting surface in a spiral shape and rotates the reflecting surface around the spiral axis so that the reflecting surface is incident parallel to the spiral axis. The helical mirror is arranged so that the incident position of the laser light is moved in the direction of the spiral axis, and the rotation driving means for rotating the helical mirror around the spiral axis is provided. Since the laser light incident in parallel with is reflected and scanning is performed by the reflected laser light, there is an effect that a small-sized and simple-structured laser scanner can be realized by using the helical mirror of the first aspect.

As described above, the laser scanner according to the invention of claim 4 is the laser scanner of claim 3, wherein the angle formed between the helical axis of the helical mirror and the reflecting surface is 4.
Since the helical mirror is set to 5 degrees and the helical mirror is rotationally driven at a constant angular velocity, a laser scanner having a small size and a simple structure can be realized by using the helical mirror of claim 2. Moreover, since the rotation driving means for rotating the helical mirror at a constant angular velocity is provided, it is possible to scan the laser beam in the spiral axis direction at a constant velocity. Therefore, for example, when this laser scanner is used in a laser printer, there is an effect that the f.theta. Lens for speed correction required in the conventional polygon mirror becomes unnecessary.

As described above, the laser scanner according to the invention of claim 5 is the laser scanner of claim 4, wherein the projection lens for refracting the laser light reflected by the reflecting surface of the helical mirror only in the spiral axis direction is used. Since it is provided, the scanning width of the laser beam can be widened in addition to the effect of the fourth aspect. As a result, it is possible to obtain a desired scanning width with a small helical mirror.

As described above, the laser scanner according to the invention of claim 6 is the laser scanner of claim 4, further comprising a rotation angle detecting means for detecting the rotation angle of the helical mirror. Since the on / off control of the laser light is performed based on this, in addition to the effect of the fourth aspect, there is an effect that the timing when modulating the laser light can be easily taken according to the image information.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, (a)
Is a perspective view showing a schematic configuration of the helical mirror, and (b) is a sectional view taken along the line AA ′ of the helical mirror in (a).

FIG. 2 is a development view of the helical mirror of FIG. 1 along a spiral axis.

3 is an explanatory diagram showing the principle of a laser scanner using the helical mirror of FIG.

FIG. 4 shows an application example of the laser scanner of FIG. 3, and is a schematic configuration diagram of an optical scanning system of a laser printer.

FIG. 5 shows a second embodiment of the present invention and is a development view along the spiral axis of the helical mirror.

6 is an explanatory view showing a laser scanner using the helical mirror of FIG.

7 is a graph showing the relationship between the x coordinate of the helical mirror of FIG. 5 and the projection position of laser light on the photosensitive drum.

[Explanation of symbols]

 1 Helical Mirror 4 Reflecting Surface 11 Semiconductor Laser 13 DC Motor 14 Rotary Encoder (Rotation Angle Detection Means) 15 Projection Lens 17 Photosensitive Drum

Claims (6)

[Claims] 1. A spiral reflecting surface is formed, and the reflecting surface is rotated about a spiral axis so that the incident position of light incident on the reflecting surface parallel to the spiral axis moves in the spiral axis direction. A helical mirror that is characterized. 2. The helical mirror according to claim 1, wherein the angle between the spiral axis and the reflecting surface is set to 45 degrees. 3. A reflection surface is formed in a spiral shape, and the reflection surface is rotated around the spiral axis so that the incident position of the laser light incident on the reflection surface parallel to the spiral axis moves in the spiral axis direction. The helical mirror and the rotation driving means for rotating the helical mirror around the spiral axis are provided. The reflecting surface of the rotating helical mirror reflects the laser light incident parallel to the spiral axis, and the reflected laser light is reflected. A laser scanner characterized by scanning with light. 4. The laser scanner according to claim 3, wherein the angle formed by the helical axis of the helical mirror and the reflecting surface is set to 45 degrees, and the helical mirror is rotationally driven at a constant angular velocity. 5. The laser scanner according to claim 4, further comprising a projection lens for refracting the laser light reflected by the reflection surface of the helical mirror only in the spiral axis direction. 6. A rotation angle detecting means for detecting the rotation angle of the helical mirror is provided, and the on / off control of the laser light is performed based on the rotation angle.
Laser scanner as described.