JPH0370174B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a light beam scanning device that projects and deflects a light beam onto an oscillating or rotating mirror and travels to a surface to be scanned. This invention relates to a device for measuring nonparallelism with respect to a swing axis or rotation axis, that is, so-called surface inclination.

[Conventional technology]

A light beam scanning means is known in which a light beam is projected onto an oscillating or rotating mirror surface in a direction perpendicular to its axis, and scans by reflecting the light beam onto the surface to be scanned. Specifically, it is required that the mirror surface be held parallel to the swing axis or rotation axis.

If this parallelism is inaccurate, the trajectory of the light beam will not match the desired scanning line.
If the replicated image is distorted, or if the angles of each mirror surface relative to the axis of rotation are different, especially in a device that uses a polygon mirror, that is, a rotating polygon mirror, the scanning pitch will be uneven.
Unsightly stripes appear on the reproduced image, significantly reducing the quality.

Therefore, when manufacturing this type of light beam scanning device, it goes without saying that the mirror itself must be manufactured accurately, and the assembly of the device must be carried out with precision and precision to meet the above requirements. ing.

[Problem that the invention seeks to solve]

Accuracy in manufacturing the mirror or device according to the above-mentioned prior art is of course necessary, but it alone is not sufficient to maintain accuracy as a light beam scanning device.

This is despite the fact that the mirror that reflects the light beam swings or rotates at a fairly high speed to deflect the light beam.
This means that detection or measurement of mirror surface tilt is only performed when the mirror is stationary.

In other words, to detect or measure the tilt of the mirror surface, mechanical measurement means or optical measurement means that projects a light beam from a direction perpendicular to the mirror surface and detects the tilt of the mirror surface based on the state of reflection is applied. However, all of these can only be applied with the mirror stationary. However, these mirrors essentially reflect the light beam while oscillating or rotating, and it is necessary that the mirror surface maintains parallelism with the axis while being oscillated. .

Conventionally, there is no known means to properly detect or measure the surface tilt of a mirror in such a driven state, so in order to maintain parallelism, the rigidity of the mechanical members that support and drive the mirror must be sufficiently increased. A common way to deal with it is to take the following measures. However, with this method, there is a tendency to set the safety factor unnecessarily large, and the dimensions of the parts become too large, resulting in a tendency for excessive quality, which may lead to disadvantages such as increased weight and higher costs.

In order to solve this problem, the present invention provides an apparatus that can reliably measure the surface tilt of a scanning mirror for light beam deflection in a driven state.

[Means for solving problems]

The device of the present invention arranges a cylindrical reflecting mirror whose central axis is parallel to the swing axis or rotation axis of the scanning mirror and passes through the light beam deflection point of the scanning mirror on the light beam projection surface of the scanning mirror, A light beam is projected onto the scanning mirror from a direction perpendicular to the axis of the scanning mirror, is projected onto the inner surface of the cylindrical reflecting mirror, and the light beam reflected by the cylindrical surface of the reflecting mirror is reflected again by the scanning mirror. , to the original light source side optical path, and based on the deviation of the light beam on the return path from the outgoing path, it is possible to detect whether or not the surface of the scanning mirror is tilted, or to measure the amount of surface tilt.

[Effect]

If there is no surface tilt in the scanning mirror, the cylindrical reflector is placed centered on the scanning mirror's light beam deflection point, so the light beam reflected from its inner surface will be reflected back to the scanning mirror's original deflection point. The light beam returns along an optical path that coincides with the optical path of the light beam projected from the light source onto the scanning mirror, and no deviation occurs between the reciprocating optical paths.

If the scanning mirror has a tilted surface, the return path of the light beam reflected from the cylindrical reflecting mirror will not match the outgoing path, and a deviation will occur in the axial direction of the scanning mirror. By detecting or measuring the direction and amount of this deviation by appropriate means, it is possible to detect or measure the surface tilt of the scanning mirror in the driving state.

〔Example〕

FIG. 1 is a schematic perspective view showing the configuration of an apparatus according to an embodiment of the present invention.

A beam of light emitted downward from a light source 1 passes through a pinhole plate 2, is reflected horizontally on the reflective surface of a half prism 3, passes through a collimator lens 4, becomes a parallel beam, and is further transformed into a parallel beam by a columnar convex lens 5. The beam is projected onto the surface of the scanning mirror 6 to be tested so as to form a linear image in the axial direction of the scanning mirror.

The light beam reflected by the scanning mirror 6 is projected onto the inner surface of the cylindrical reflecting mirror 8, and travels in the circumferential direction of the reflecting mirror 8 due to the swinging of the scanning mirror 6. Reflector 8
is arranged at a position where its central axis coincides with the swing axis of the scanning mirror 6, and therefore the scanning mirror 6
If the surface of mirror 8 is made precisely to coincide with its pivot axis, that is, if there is no surface tilt, the light beam will be projected perpendicularly to the pivot axis of reflector 8.

The returning light beam that is reflected by the surface of the reflecting mirror 8 is incident perpendicularly to the swing axis of the reflecting mirror 8, so it passes through the same optical path as the outward path and forms a linear image at the deflection point of the scanning mirror 6. The light is reflected and enters the half prism 3 through the columnar convex lens 5 and the collimator lens 4. And part of that luminous flux is transmitted through half prism 3
The light beam passes through the light beam, travels straight, and forms an image as an original pinhole image on the two-split photoelectric conversion element 9, which detects the deviation of the projection position of the light beam.

As shown in FIG. 2, the two-split photoelectric conversion element 9 has photoelectric conversion elements 9a and 9b of the same performance vertically adjacent to each other, and when the light beam passes through the same optical path as the outward path to the half prism 3, That is,
The scanning mirror 6 is arranged so that the boundary line between the two elements is located at the position where the center of the light beam is projected when the scanning mirror 6 has no surface tilt.

Therefore, if the scanning mirror 6 does not have a tilted surface, the light beam is equally divided into upper and lower parts by the boundary line, as shown in FIG.
The amount of light received by b is equal, and the output levels of both are the same.

On the other hand, if the scanning mirror 6 has a tilted surface, the light beam reflected by the scanning mirror 6 will not be incident perpendicularly to the swing axis of the reflecting mirror 8.
The incident point of the reflected light beam is shifted from the first reflection point, and is reflected again by the scanning mirror 6, which has a tilted surface, so that the amount of deflection is doubled, and the light beam is projected onto the photoelectric conversion element 9. The light beam is shifted either upward or downward depending on the direction of the surface tilt.

Therefore, as shown in FIG. 2B, the amounts of light received by the two photoelectric conversion elements 9a and 9b are different, resulting in a difference in their output levels. This difference in output level is
By measuring with an appropriate means and detecting which side has a higher level output, it is possible to know whether the scanning mirror 6 is tilted or not and its direction.

Note that the amount of deviation or the angle of deviation of the light beam varies depending on the angular position during the swing stroke of the scanning mirror 6, and the smaller the incident angle (φ) of the light beam with respect to the mirror surface, the greater the deviation. The quantity is large. what if,
Assuming that the surface of the scanning mirror directly faces the incident light beam (deflection angle of 180 degrees), the deflection angle of the light beam is determined by the angle of deflection of the scanning mirror 6, as is clear from the geometrical consideration in FIG. On the other hand, if the scanning mirror surface is parallel to the light beam (deflection angle 0 degrees), no deviation occurs. Therefore, if the scanning mirror 6 has a tilted surface, the trajectory of the light beam scanning the cylindrical reflecting mirror 8 will be tilted in a spiral manner as shown by the dotted line in FIG. The projection position also swings up and down according to the swing period of the mirror, as shown in FIG. 2B.

For this reason, the device of this embodiment is not suitable for measuring the amount of deviation of a light beam, but in actual work,
Knowing whether a scan mirror has a tilt and, if so, its direction, is sufficient to accomplish the adjustment; Considering that there was no means to detect this occurrence, the present invention has great significance.

The above has described an embodiment in which the present invention is applied to a device for detecting the tilting of the surface of a swing-type scanning mirror. However, by adding some modifications to the above-mentioned means, when the scanning mirror has a tilting of the surface, the amount,
In other words, the device can be used to measure the angle of surface inclination.

FIG. 4 is a schematic perspective view showing the configuration of the first embodiment of the device, which includes a light source 1, a pinhole plate 2, a half prism 3, a collimator lens 4, a columnar convex lens 5,
The scanning mirror 6 to be measured and the galvanometer 7 are exactly the same as in the first illustrated embodiment.

In the device shown in the fourth figure, the cylindrical mirror 10 on which the light beam reflected by the scanning mirror 6 is projected has a narrow width as shown in the figure. The photoelectric conversion element is an array sensor 11 in which a large number of small elements are arranged vertically at a required pitch.

That is, in the fourth illustrated apparatus, among the light beams reflected and deflected by the scanning mirror 6, only the light beams within a certain limited deflection range are reflected by the cylindrical mirror 10. Even if the scanning mirror 6 has a tilted surface and the light beam travels diagonally, the width of the cylindrical mirror 10 is small, so the difference in height between the projection points of the light beam at both ends can be virtually ignored. Therefore, the light beam is projected onto a specific position of the arrayed sensor 11, and an output is obtained from a specific one of the many photoelectric conversion elements constituting the sensor.

Therefore, depending on which of these many photoelectric conversion elements has an output, the position of the projection point of the light beam can be known, and the amount of deviation from the projection point when the scanning mirror 6 is not tilted can be calculated. Can be measured.

As shown in the fourth figure, the cylindrical mirror 10 is
When installed at a position that receives a light beam reflected at a right angle (90 degrees) with an incident angle φ = 45 degrees to the surface of the scanning mirror 6, the deflection angle of the light beam incident on the sensor 11 is determined by the oscillation of the scanning mirror 6. If the surface tilt angle with respect to the moving axis is "θ", then geometrically "√2・
.theta.', the surface tilt angle of the scanning mirror 6 can be easily determined from the above deviation amount and optical path length by trigonometric calculation using the following formula.

θ≒tan ^-1 (d/2a+2b)/√2 where θ: Surface tilt angle d: Light beam detection point deviation amount a: Distance between scanning mirror and cylindrical mirror b: Distance from scanning mirror to sensor If, If the cylindrical mirror 10 is arranged not at right angles to the light beam incident on the scanning mirror 6 but substantially in the same direction as the light beam, that is, with an incident angle φ = 0°, the reflected light beam will reach the sensor 11. Since the incident angle is "4θ" as shown in the third diagram, a simpler calculation formula can be applied. In this case, it is actually impossible to place the cylindrical mirror on the incident optical path of the light beam to the scanning mirror, so it will be installed slightly to the side, but the error will not be large enough to cause problems in the measured values. Since this does not occur, it is sufficient for practical use.

In the above embodiment, a narrow cylindrical mirror 10 is used, but a mask having a slit of the required width in the left and right direction is placed in front of the wide mirror shown in the first figure. , the slit portion may be configured to be movable along the cylindrical mirror so that the slit portion can be set at a desired position.

In the above-mentioned measurement, if the angle of inclination of the surface of the scanning mirror 6 is small and the amount of deviation of the projection point of the light beam is only a minute amount, in order to measure it, it is necessary to use the unit photoelectric conversion that constitutes the array sensor 11. The device must be made extremely small, which poses a practical problem.

FIG. 5 shows one means for dealing with this problem, in which a two-split photoelectric conversion element 12 similar to the device shown in the first figure is supported so as to be movable up and down along a guide 13, and fixed to the element 12. Nut 14 and screw shaft 15
This is the result of engagement. By rotating the screw shaft 15 while holding the handle 16, the element 12 is slightly moved up and down, and the pair of photoelectric conversion elements is moved to a position where the light beam is evenly received. Read the rotation amount of 15,
The amount of movement of the element 12 is measured.

According to this, even when the amount of deviation of the projection point of the light beam is minute, it can be measured extremely accurately, and the state of the surface tilt of the scanning mirror can be measured with high precision.

The above explanation describes each embodiment in which the present invention is applied to a device for detecting or measuring the surface tilt of a reciprocating type scanning mirror. Needless to say, it can also be applied to things.

In addition, multiple mirrors are arranged in a polygonal column shape,
It can also be applied to so-called polygon mirrors. However, in the case of polygon mirrors, the state of surface tilt on each surface is not necessarily constant, so
Care must be taken to ensure that the above-mentioned detection or measurement can be performed on a desired mirror surface.

FIG. 6, FIG. 7, and FIG. 8 are perspective views showing essential parts of an embodiment of an apparatus for applying the present invention to a polygon mirror, respectively.

FIG. 6 shows a bevel gear 20 fitted onto a drive shaft 19 that rotates a polygon mirror 18 by a motor 17, a horizontal shaft 22 via a bevel gear 21 that meshes with the bevel gear 20, and a disk fitted onto the shaft 22. The shutter plate 23 of the shape is rotated. The shutter plate 23 is provided with a notch 24 in a part of its periphery, and a light beam is irradiated onto the polygon mirror 18 through this notch 24.

Since the bevel gears 20 and 21 have the same number of teeth, the polygon mirror 18 and shutter plate 23 have the same number of teeth.
The polygon mirrors 18 rotate synchronously and only when a specific reflective surface of the polygon mirror 18 is in a position to reflect the light beam.
The light beam passes through the notch 24 and is blocked by the shutter plate 23 from other reflective surfaces. Therefore, if the means shown in FIG. 6 is used in place of the scanning mirror 6 and galvanometer 7 of the devices shown in FIGS. 1 to 4, it is possible to detect or measure the surface inclination of only the specific reflecting surface. In addition, in the case of a polygon mirror,
Since the position of the mirror surface does not match the rotation axis,
Although the projection point to the photoelectric conversion element swings slightly from side to side,
There is no problem in detecting or measuring surface tilt.

It goes without saying that the notch 24 provided in the shutter plate 23 should have an angular range that corresponds to the number of reflective surfaces of the polygon mirror 18, and should also be used to detect or measure surface tilt. It goes without saying that the rotational phase relationship between the polygon mirror 18 and the shutter plate 23 should be adjustable depending on the reflecting surface. For example, the shutter plate 23 may be made rotatable about the shaft 22 and fixed at a desired position.

Next, FIG. 7 shows that the polygon mirror 26, which is rotationally driven by the motor 25, has a shutter plate 28 fitted onto the shaft 27, and a part of the notch 29 formed on the periphery of the shutter plate 28.
The notch 29 is detected by a light source 30 and a photoelectric element 31 arranged oppositely above and below the shutter plate 28, and based on the detection signal, a shutter means 33 is arranged in the optical path of the light beam via a control circuit 32. It is designed to control.

That is, the light beam from the light source 30 is transmitted to the notch 29.
If the shutter means 33 is controlled to transmit the light beam based on the detection signal outputted from the photoelectric element 31 only while the light beam is passing through the light beam, it is possible to avoid the trouble of only transmitting the light beam with respect to a specific reflective surface, as in the device shown in the sixth figure. can be detected or measured.

As the shutter means 33, a device that can be controlled to transmit or block the light beam according to an electric signal, such as a liquid crystal element, can be used. Also, when the light beam is a coherent laser beam as shown in FIG. An acousto-optic light modulator or the like can be applied. In FIG. 8, 41 is a laser beam light source, 42 is a beam expander, and 43 is an acousto-optic modulator.

〔Effect of the invention〕

(1) It is possible to detect or measure the state of the surface tilt of the mirror that deflects and scans the light beam while it is in operation.

(2) Detection or measurement can be performed without contacting the mirror surface, so there is no risk of damaging the mirror surface.

(3) It can be applied to either a reciprocating oscillating mirror or a rotating mirror, as well as a single mirror or a polygon mirror.

(4) There are no moving parts other than the original movement of the mirror to be measured, allowing accurate detection or measurement in a stable state.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing a two-split photoelectric conversion element, and FIG.
The figure shows a reflected optical path of a light beam, FIG. 4 is a perspective view showing the configuration of another embodiment of the present invention, and FIG. 5 shows another embodiment of a photoelectric conversion element applied to the same embodiment. The perspective view, FIG. 6, FIG. 7, and FIG. 8 are perspective views showing main parts when the present invention is applied to a polygon mirror, respectively. DESCRIPTION OF SYMBOLS 1... Light source, 2... Pinhole plate, 3... Half prism, 4... Collimator lens, 5... Columnar convex lens, 6... (oscillating type) scanning mirror, 7...
...Galvanometer, 8...Cylindrical mirror, 9...
Two-split photoelectric conversion element, 10...Cylindrical mirror, 1
1... Array sensor, 12... Two-split photoelectric conversion element, 13... Guide, 14... Nut, 15
... Screw shaft, 16 ... Handle, 17 ... Motor, 18 ... Polygon mirror, 19 ... Axis, 2
0, 21...Bevel gear, 22...Shaft, 23...Shutter plate, 24...Notch, 25...Motor, 26...Polygon mirror, 27...Shaft, 28
... Shutter plate, 29 ... Notch, 30 ...
Light source, 31...Photoelectric element, 32...Control circuit, 3
3... Shutter, 41... Laser beam light source, 42... Beam expander, 43... Acousto-optic light modulation element.

Claims (1)

[Scope of Claims] 1. A light source that projects a light beam, a swinging or rotating mirror that reflects the light beam onto a surface to be scanned and travels, and a shaft that passes through the reflection point of the mirror and whose swing axis or rotation An internally reflecting cylindrical mirror centered on an axis parallel to the axis, and detecting the deviation of the light beam optical path reflected by the cylindrical mirror and re-reflected by the swinging or rotating mirror with respect to the projection side light beam optical path. Or a device for detecting or measuring the surface tilt of a scanning mirror for light beam deflection, which includes photoelectric means for measuring. 2. A patent claim characterized in that a light beam from a light source is projected through a half prism or a half mirror, and the light source is disposed on one side of the optical path branched by the half prism or half mirror, and the photoelectric means is disposed on the other side. A device according to scope 1. 3. The device according to claim 1 or 2, wherein the photoelectric means is composed of a plurality of photoelectric conversion elements arranged in a direction parallel to the central axis of the cylindrical mirror. 4. The device according to claim 3, wherein the photoelectric means is a two-part photoelectric element. 5. The device according to claim 3, wherein the photoelectric means is an array sensor in which a large number of photoelectric elements are arranged in a row. 6. Any of the preceding claims, characterized in that the effective width of the cylindrical mirror in the scanning direction is made small to such an extent that the projection position of the light beam onto the photoelectric means is substantially at a fixed position. The device described in.