JPH0222528A - Method for measuring surface tilt angle of polygon mirror - Google Patents

Abstract

PURPOSE:To easily and accurately find the relative surface tilt angle between mirror surfaces by photodetecting a reflected light form the polygon mirror by photodetectors arranged above and below about the scanning direction of the reflected beam. CONSTITUTION:The polygon mirror 1 is irradiated with the light beam 3 from a light source 2 and its reflected beam 4 is photodetected 5. This photodetection part 5 consists of the upper photodetector 51a and lower photodetector 51b about the scanning direction 53 of the beam 4. Then the photodetectors 51a and 51b are moved up and down so that the outputs of the photodetectors 51a and 51b are equal to each other, and their movement positions are read by a measurement and display part 6 to obtain the direction center position of the beam 4. Namely, the direction position of the beam 4 between mirror surfaces is found and the direction position distance DELTAX between the mirror surfaces is found, so that the surface tilt angle theta is found from theta=DELTAX/2L, where L is the distance between a mirror surface of the polygon mirror 1 and the photodetection part 5.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to optical printers such as laser printers, optical display devices, etc., in which a polygonal mirror is used to scan a light beam. This invention relates to a method for measuring relative surface inclination angle.

(Prior Art) Optical printers, such as laser printers, use a polygon mirror that rotates at high speed to direct and scan a light beam containing so-called printed information, such as characters and images, onto a photosensitive medium. Printing is performed by

By the way, in recent years there has been an increasing demand for improving the image quality of such optical printers, but image quality is determined, in part, by the scanning accuracy of the light beam, that is, the scanning pitch of the light beam. It depends on whether or not it is always constant. This scanning accuracy depends on the difference in the face tilt angle between each mirror surface, which is caused by the manufacturing precision of the polygon mirror and the shaft vibration during rotation, and if there is a difference in the face tilt angle, the scanning position of the light beam will There will be a shift, and the pitch will no longer be -like.

In this way, the scanning accuracy of the light beam depends on the manufacturing accuracy of the polygon mirror and the axial wobbling during rotation, but during manufacturing, it is necessary to make sure that there is no difference in the surface tilt angle between each mirror surface, and to completely eliminate axial wobbling. It is very difficult to lose it, so
When manufacturing or using a polygon mirror, it is essential to measure and evaluate the angle of inclination. Therefore, while rotating the polygon mirror, measures are taken to measure the relative tilt angle between each mirror surface, and based on the difference, measures are taken such as changing the incident angle of the light beam. Several measurement methods have been proposed.

For example, Japanese Patent Application Laid-Open No. 61-73917 discloses that a rotating polygon mirror is irradiated with a light beam, and the reflected beam from the polygon mirror is received by light receivers fixed at the upper and lower sides in the scanning direction. A method is described in which light is received by an element and the surface tilt angle is determined from the ratio of outputs between both light receiving elements. However, this method has a problem in that since the light receiving element is fixed, measurement errors become large when the intensity distribution of the irradiated light beam is not a Gaussian distribution. Furthermore, since the light-receiving element is still fixed, there is also the problem that measurement accuracy largely depends on the photoelectric conversion characteristics of the light-receiving element.

On the other hand, JP-A-62-172318 discloses that pulsed light is irradiated onto the entire surface of a predetermined mirror surface of a rotating polygon mirror via an autocollimator, and the imaging position of the reflected light from each mirror surface is A method for determining the surface inclination angle from the difference between the two is described.

However, although this method has the advantage of being able to measure the surface tilt angle corresponding to each mirror surface of a polygon mirror, it requires an expensive autocollimator and has the problem that the device configuration becomes large-scale. Furthermore, since the entire surface of the mirror is irradiated with light, there is a problem in that the measurement is susceptible to the influence of light reflected from portions other than the so-called effective mirror surface that is actually used for scanning the light beam.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the conventional method, and easily and accurately calculates the relative tilt angle between each mirror surface of a rotating polygon mirror. The purpose is to provide a method for measuring.

(Means for Solving the Problems) To achieve the above-mentioned objects, the present invention provides the following features when measuring the relative surface inclination angle between each mirror surface of a polygon mirror for scanning a light beam: (a) during rotation; A light beam is irradiated onto the polygon mirror above the mouth,
The reflected beam from the polygon mirror is received by light receiving elements arranged above and below in the scanning direction of the reflected beam, c. For each of the above mirror surfaces, a. The outputs of the above upper and lower light receiving elements are equal to each other. Move the upper and lower light-receiving elements in the vertical direction as shown in FIG. It is characterized by a method of measuring the face tilt angle of a polygon mirror.

(Function) In the present invention, a light beam is irradiated with respect to an arbitrary mirror surface of a rotating polygon mirror, and the reflected beam is received by light receiving elements arranged above and below in the scanning direction. The light receiving elements are moved up and down so that the outputs are equal to each other. Then, the position after the movement is set as the directional position of the reflected beam.

The directional position of the reflected beam is determined for each mirror surface, and the surface tilt angle θ between each mirror surface is determined from the distance ΔX between the directional positions between each mirror surface and the distance from the mirror surface to the light receiving element based on the following formula. .

θ=ΔX/2L (Embodiment) In FIG. 1, a light beam 3 such as a laser beam is irradiated from a light source 2 onto a polygon mirror 1 (number of mirror surfaces = 8) that is rotating in the direction of the arrow at an arbitrary speed. At the same time, the beam 4 reflected by the polygon mirror 1 is received by the light receiving section 5.

As shown in FIG. 2, the light receiving section 5 consists of a light receiving element 51a located on the north side and a light receiving element 51b located on the lower side with respect to the scanning direction 53 of the reflected beam.
The reflected beam that is scanned in a pattern of 2 can be simultaneously received by these upper and lower light receiving elements 51a and 51b.

The measurement position within the mirror surface is determined by the position of the light receiving section 5 in the operating direction.

As shown in FIG. 3, the light receiving section 5 obtains an output a from the light receiving element 51a and an output from the light receiving element 51b. Therefore, while observing these forces a and b with the oscilloscope 8, the light receiving elements 51a and 51b are simultaneously moved in the vertical direction so that both forces are equal to each other. At this time, the correspondence between the outputs a and b and each mirror surface is determined as follows.

That is, in FIGS. 1 to 3, first, the light receiving element 5
The outputs a and b of the outputs 1a and 51b are added by an adder circuit 71 of the synchronizing signal generating section 7 to obtain a signal shown as C in FIG. next,
This signal C is shaped into a pulse signal d by a shaping circuit 72, and the pulse signal d is further counted by a counter circuit 73 to create a 4-bit signal. A synchronization signal e having a period equal to the rotation period of mirror 1 is obtained. By applying a trigger to this synchronization signal e and viewing the signals a and b with the oscilloscope 8, it is possible to associate the signals a and b with each mirror surface of the polygon mirror 1.

Now, as mentioned above, the two light receiving elements 51a and 51b
Both light receiving elements 51
a and 51b in the vertical direction.

Then, if the movement position is read by the measurement/display unit 6,
This is the directional center position of the reflected beam 4.

The light receiving elements 51a and 51b can be moved by, for example, a micrometer head attached to the light receiving part 5, and the distance of movement can be measured and displayed by, for example, a linear gauge.

If the directional position of the reflected beam is determined for each mirror surface and the distance ΔX between the directional positions between each mirror surface is determined, then from this and the distance between the mirror surface of the polygon mirror 1 and the light receiving section 5, the above formula, i.e. , the surface inclination angle can be determined based on the formula, θ=ΔX/2L.

(Effects of the Invention) In the present invention, a beam reflected by a polygon mirror is received by light-receiving elements arranged above and below in the scanning direction of the reflected beam, and for each mirror surface, the outputs of the above-mentioned upper and lower light-receiving elements are The upper and lower light-receiving elements are moved in the vertical direction so that they are equal to each other, and the position after the movement is used as the directional position of the reflected beam, and the distance between the directional positions between the mirror surfaces is converted into a surface tilt angle. Easily calculate the relative surface tilt between mirror surfaces for any position of the mirror surfaces.
Moreover, it can be determined with high precision, and unlike the conventional methods mentioned above, there is no measurement error caused by the intensity distribution of the light beam or the characteristics of the photodetector, and there is no need for an expensive autocollimator. There's nothing to do.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing one embodiment of the present invention;
Fig. 2 is a schematic front view of the light receiving part showing the relationship between the light receiving part and the scanning direction of the reflected beam, and Fig. 3 shows the signals and their timings of each part in the embodiment G shown in Fig. 1 above. This is a chart showing. 1: Polygon mirror 2: Light source 3: Light beam 4: Reflected beam 5: Light receiving section 51a: Upper light receiving element 51b: Lower light receiving element 52: Scanning locus of reflected beam 53: Scanning direction of reflected beam 6: Measurement/display section 7: Synchronous signal generation section 71: Adder 72: Shaping circuit 73: Counter circuit 74: Synchronous signal generation circuit Nioscilloscope

Claims (1)

[Claims] When measuring the relative angle of inclination between mirror surfaces of a polygon mirror for scanning a light beam, (a) irradiating the rotating polygon mirror with a light beam; (b) irradiating the polygon mirror while it is rotating; The beam reflected by the mirror is received by light receiving elements arranged above and below in the scanning direction of the reflected beam, c. For each of the above mirror surfaces, a. The outputs of the above above upper and lower light receiving elements are made equal to each other. moving the upper and lower light-receiving elements in the vertical direction; b. converting the distance between the pointing positions between each of the mirror surfaces into a surface inclination angle, with the position after the movement as the pointing position of the reflected beam; A method for measuring the tilt angle of a polygon mirror.